candle water experiment independent variable

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Candle burning investigation

By Tim Jolliff

• No comments

Engage learners in the experimental process as they develop a hypothesis and plan an investigation

This resource accompanies the article Understanding the hypothesis , part of the Teaching science skills series, from Education in Chemistry.

Learning objectives

1 Make predictions using your scientific knowledge and use them to form a hypothesis.

2 Plan an appropriate investigation to test your predictions.

Download this

Download the slides as PowerPoint and pdf , teacher notes as Word and pdf and student worksheet as Word and pdf .

Introduction

Experiments ‘to show’ can be frustrating for learners if they already know what the experiment will show. The approach here is to change the experiment into one where they will not know what happens.

Learners have to use critical thinking to evaluate the alternative suggestions in the concept cartoon. They are then asked to formulate a hypothesis based on their own ideas about what will happen. They will need experimental data in order to test their prediction.

As learners are asked to plan an investigation to test their hypothesis they are prompted to think about what makes a fair test and how to get reliable data.

How to use the resource

This could be used to follow on from a class investigation into the effect of beaker size on the length of time the candle burnt. The slides can be used to guide a class discussion, in combination with or as an alternative to the worksheets. Give learners time to read the concept cartoon and consider their own ideas, then discuss and work towards agreeing on a hypothesis to test.

Alternatively, learners can work through the worksheet in groups, or independently as a homework task.

If the learners plan and carry out their own investigations this will be an activity for a whole lesson or even two. Otherwise all or part can be used as an activity at the start or end of a lesson.

There is an opportunity to evaluate some real experimental data (this might motivate learners to carry out the experiment to obtain better evidence). Learners are then asked to briefly think about the difficulties of showing only slight effects in results, as in medical research.

The follow-up task asks learners to use creative skills to produce their own concept cartoons. You can show learners more examples of concept cartoons from  our collection .

Differentiation

This activity was created to be challenging, requiring learners to use critical thinking. By structuring as a class discussion you can use the discussion guidance in the teacher notes to offer prompts or ask questions to help guide learners needing more support. Alternatively, asking learners to work in small groups for some parts of the activity will give them a chance to support one another. More confident learners could complete the worksheet independently.

Answers and discussion guidance can be found in the teacher notes.

More resources

• Use  research-based tips  to help learners form scientific questions. 
• Discover ideas for open investigations where learners can practise developing hypotheses with activities from  In search of solutions . 
• Explore the reactivity series of metals and displacement reactions with these  experiments and videos for 14–16 students , use the pause-and-think questions to discuss what is being tested and why. 
• Find out how  senior principal scientist, Misbah  uses computers to help make and test predictions about catalysts.

Candle investigation: hypothesis and planning - presentation

Candle investigation: hypothesis and planning - teacher notes, candle investigation: hypothesis and planning - student worksheet, additional information.

This resource was originally created by the author as part of our Chemistry for the gifted and talented collection. It has been updated and made more accessible.

• 11-14 years
• 14-16 years
• Presentation
• Reactions and synthesis
• Communication skills
• Able and talented

Specification

• WS.2.1 Use scientific theories and explanations to develop hypotheses.
• WS.2.2 Plan experiments or devise procedures to make observations, produce or characterise a substance, test hypotheses, check data or explore phenomena.
• WS2.1 Use scientific theories and explanations to develop hypotheses.
• WS2.2 Plan experiments or devise procedures to make observations, produce or characterise a substance, test hypotheses, check data or explore phenomena.
• 2a Use scientific theories and explanations to develop hypotheses
• 2b Plan experiments or devise procedures to make observations, produce or characterise a substance, test hypotheses, check data or explore phenomena
• IaS1.1 in given contexts use scientific theories and tentative explanations to develop and justify hypotheses and predictions
• IaS1.6 plan experiments or devise procedures by constructing clear and logically sequenced strategies to: make observations, produce or characterise a substance, test hypotheses, collect and check data, explore phenomena
• WS.1.2a Use scientific theories and explanations to develop hypotheses
• WS.1.2b Plan experiments or devise procedures to make observations, produce or characterise a substance, test hypotheses, check data or explore phenomena
• applying knowledge of chemistry to new situations, interpreting information and solving problems
• planning or designing experiments to test given hypotheses or to illustrate particular effects, including safety measures
• use scientific theories and explanations to develop hypotheses
• plan experiments or devise procedures to make observations, produce or characterise a substance, test hypotheses, check data or explore phenomena
• use scientific theories and explanations to develop hypotheses;
• plan experiments or devise procedures to make observations, produce or characterise a substance, test hypotheses, check data or explore phenomena;
• 2. Recognise questions that are appropriate for scientific investigation, pose testable hypotheses, and evaluate and compare strategies for investigating hypotheses.
• 3. Design, plan and conduct investigations; explain how reliability, accuracy, precision, fairness, safety, ethics, and the selection of suitable equipment have been considered.
• 4. Produce and select data (qualitatively/ quantitatively), critically analyse data to identify patterns and relationships, identify anomalous observations, draw and justify conclusions.
• 5. Review and reflect on the skills and thinking used in carrying out investigations, and apply their learning and skills to solving problems in unfamiliar contexts.

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Why does the water rise?

It's a very popular experiment ( eg ), from elementary school : put a burning candle on a dish filled with water, cover the candle with an inverted glass: after a little while, the candle flame goes out and the water level inside the glass rises.

The standard explanation (as I recall it) was that combustion "burns" oxygen, and the consummed volume accounts for the extra water that goes inside the glass. Is this correct? I remember feeling (years later) uncomfortable with the explanation, because "to burn" is certainly not "to dissapear": I thought that oxygen combustion produces (mainly) $CO_2$ and hence one oxygen molecule would produce another $CO_2$ molecule, and the volume would remain basically the same. Perhaps $CO_2$ dissolves into the water? I would doubt that.

To add to my confusion, others state that the main cause is not the oxygen combustion but the changes of air temperature, that decreases when the flame goes out and makes the air inside the glass contract... which would rather invalidate the experiment as it was (and is) traditionally taught to students.

What is the right explanation?

(image from here )

Update : As from webpage linked in accepted answer, there are several effects here, but it's fair to say that the "traditional" explanation (consumption of oxygen) is wrong. Oxygen (plus paraffin) turn into $CO_2$ (plus water) (a representative reaction: $C_{25}H_{52}+38O_2 \to 25CO_2+26H_2O$ ). This would account for a small reduction in volume ( $25/38 \approx 2/3$ ), even assuming that this is the complete chemical picture (it's not) and that water condenses ( $CO_2$ dissolves in water poorly and very slowly). The main cause here is thermal expansion-contraction of air.

• home-experiment
• physical-chemistry

• $\begingroup$ Is there a stackexchange for chemistry? Maybe they could provide better help. $\endgroup$ –  Lemon Commented Jan 4, 2012 at 1:58
• $\begingroup$ @jak Not yet. $\endgroup$ –  Manishearth Commented Mar 15, 2012 at 7:21
• $\begingroup$ @Manishearth Yes there is - chemistry.stackexchange.com It is in beta, though. $\endgroup$ –  Dave Coffman Commented Jul 28, 2014 at 22:06
• $\begingroup$ @DaveCoffman look at the date on that comment. I moderate Chem.SE, I know about it :P $\endgroup$ –  Manishearth Commented Jul 28, 2014 at 22:28
• $\begingroup$ Geez - Sorry about that. $\endgroup$ –  Dave Coffman Commented Aug 2, 2014 at 18:19

3 Answers 3

I found two web pages that explain the phenomenon quite well, and even looks into the misconceptions people have.

The candle flame heats the air in the vase, and this hot air expands. Some of the expanding air escapes out from under the vase — you might see some bubbles. When the flame goes out, the air in the vase cools down and the cooler air contracts. The cooling air inside of the vase creates a vacuum. This imperfect vacuum is created due to the low pressure inside the vase and the high pressure outside of the vase. We know what you're thinking, the vacuum is sucking the water into the vase right? You have the right idea, but scientists try to avoid using the term "suck" when describing a vacuum. Instead, they explain it as gases exerting pressure from an area of high pressure to an area of low pressure. A common misconception regarding this experiment is that the consumption of the oxygen inside of the bottle is also a factor in the water rising. Truth is, there is a possibility that there would be a small rise in the water from the flame burning up oxygen, but it is extremely minor compared to the expansion and contraction of the gases within the bottle. Simply put, the water would rise at a steady rate if the oxygen being consumed were the main contributing factor (rather than experiencing the rapid rise when the flame is extinguished). (1)

The page from Harvard goes into more detail on the argument versus the error for the incorrect statement.

Argument : Oxygen is replaced by Carbon dioxide. So, there is the same amount of gas added than taken away. Therefore, heat alone most be responsible for the water level change. Source of the Error : A simplified and wrong chemical equation is used, which does not take into account the quantitative changes. The chemical equation has to be balanced correctly. It is not true that each oxygen molecule is replaced by one carbon dioxide molecule during the burning process; two oxygen molecules result in one carbon dioxide molecule and two water molecules (which condense). Remember oxygen is present in the air as a diatomic molecule. [A reader clarifies the water condensation in an email to me as follows: If the experiment were done with the sealing fluid able to support a temperature greater than 212 F and the whole system held above this temperature then the water product of combustion would remain gaseous and the pressure within the vessel would increase as a result of three gaseous molecules for every two prior to combustion and the sealing fluid would be pushed out.] Argument : Carbon dioxide is absorbed by the water. Thats why the oxygen depletion has an effect. Source of the Error : This idea is triggered from the fact that water can be carbonized or that the oceans absorb much of the carbon dioxide in the air. But carbon dioxide is not absorbed so fast by water. The air would have to go through the water and pressure would need to be applied so that the carbon dioxide is absorbed during the short time span of the experiment. Argument : The experiment can be explained by physics alone. During the heating stage, air escapes. Afterwards, the air volume decreases and pulls the water up. Source of the Error : the argument could work, if indeed the heating of the air would produce enough pressure that some air could leave. In that case, some air would be lost through the water. But one can observe that the water level stays up even if everything has gone back to normal temperature (say 10 minutes). No bubbles can be seen. Argument : It can not be that the oxygen depletion is responsible for the water raising, because the water does not rise immediately. The water rises only after the candle dims. If gas would be going away, this would lead to a steady rise of the water level, not the rapid rise at the end, when the candle goes out. Source of the Error : It is not "only" the oxygen depletion which matters. There are two effects which matter: the chemical process of the burning as well as a physical process from the temperature change. These effects cancel each other initially. Since these effect hide each other partially, they are more difficult to detect. (2)

It clearly has more to do with the temperature differences than any conversion of gases. Especially considering that a volume of oxygen and carbon dioxide will be nearly identical to human eye observation.

• 4 $\begingroup$ I'd trust Harvard (second footnote I am guessing). $\endgroup$ –  Skava Commented Jan 4, 2012 at 3:11
• 2 $\begingroup$ Yes "Skava", now go to bed! $\endgroup$ –  Larian LeQuella Commented Jan 4, 2012 at 3:12
• 3 $\begingroup$ This answer is useful in pointing the best explanation I've seen (the second link), but the text is plainly copied other pages (should be formatted as quotes) and does not make clear the general summary/conclusion. $\endgroup$ –  leonbloy Commented Jan 4, 2012 at 13:49
• $\begingroup$ I'd question one thing from that answer, though: Nowhere is a vacuum created. There's always air in the glass, and it always fills the whole space not occupied by water. When the air cools down, it doesn't contract by itself, only its pressure goes down (intuitively: Since the molecules get slower, they hammer less onto the water surface). As result the water is pressed more in by the air outside than out by the air inside, and thus flows inside. This rising water compresses the air inside, which causes air density and thus pressure inside to rise again until equilibrium is reached. $\endgroup$ –  celtschk Commented Jan 18, 2012 at 5:47
• 1 $\begingroup$ The second quotation seems to contradict the first one: first says "you might see some bubbles", the second one: "No bubbles can be seen". $\endgroup$ –  Ruslan Commented Jul 4, 2018 at 9:25

I have not actually tried this experiment, but I will make at least a few observations:

Hypothesis 1: The burning of oxygen is responsible for the reduced air pressure.

Prediction - if the burning of oxygen is the sole cause of the change in pressure, we should expect to see the water in the glass rise at a more or less constant rate from the moment the environment is sealed until the burning stops. After the candle extinguishes, there should be no more change in water level.

Hypothesis 2: The reduction in temperature after the candle extinguishes is responsible for the reduced air pressure.

Prediction - if the temperature change is the sole cause of the change in pressure, we should expect to see no change in water level while the candle is burning (in the limit that the glass was lowered very slowly). After the burning stops, the water should rise at a rate related to the temperature drop and eventually stop as the experimental setup comes to room temperature.

In order to test which explaination is correct, you should be able to merely perform the experiment and match the observation with the prediction. Of course, in real life it may be a combination of these two factors or perhaps include other reasons not listed here.

Additional measures such as putting an oxygen indicator in the glass (say a fresh slice of apple) or a thermometer would provide further insight.

• 1 $\begingroup$ As oxygen is burned - how many moles of CO2 do you get for each mole of O2 used? $\endgroup$ –  Martin Beckett Commented Jan 3, 2012 at 23:15
• 1 $\begingroup$ @MartinBeckett: Not to mention it's mostly carbon monoxide because it's imperfect burning. $\endgroup$ –  Mike Dunlavey Commented Jan 4, 2012 at 3:15
• 1 $\begingroup$ @MartinBeckett: The pertinent equation seems to be something like $C_{25} H_{52} + 38 O_2 => 25 C O_2 + 26 H_2 O$. So for 1 mole of oxygen we have 0.65 moles of $C O_2$ - a moderate reduction, and this assuming water condenses. $\endgroup$ –  leonbloy Commented Jan 4, 2012 at 14:40
• 1 $\begingroup$ @leonbloy - although with a smoky candle you do get a lot of CO. Plus since O2 is only 20% of air it would at most be a (1-0.65)*0.21 = 7% change in volume even with full combustion $\endgroup$ –  Martin Beckett Commented Jan 4, 2012 at 16:26
• $\begingroup$ @MartinBeckett: you are right, of course. See the Harvard link in the other answer for the complete picture. $\endgroup$ –  leonbloy Commented Jan 4, 2012 at 16:36

I will make this into an answer because the idea behind this question is used in an ancient medical metho d which was still used by practical nurses and even prescribed by old fashioned doctors when I was a child more than half a century ago in Greece. It is now used in alternative medicine practices

The air inside the cup is heated and the rim is then applied to the skin, forming an airtight seal. As the air inside the cup cools, it contracts, forming a partial vacuum and enabling the cup to suck the skin, pulling in soft tissue, and drawing blood to that area.

I think it was the invention of antibiotics which diminished rapidly its use, which was mainly for bronchitis pneumonia and similar afflictions, at least in Greece.

As far as the question goes, no liquids to confuse the issue of its being a strongly temperature dependent effect.

• $\begingroup$ Indeed, the practice is known as "cupping" and is often offered at spas and other health resorts. $\endgroup$ –  AdamRedwine Commented Jan 4, 2012 at 13:15
• $\begingroup$ +1 In spanish: "ventosa". I've seen it applied by my grandmother many years ago. $\endgroup$ –  leonbloy Commented Jan 4, 2012 at 13:37

Not the answer you're looking for? Browse other questions tagged water home-experiment physical-chemistry or ask your own question .

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Science in School

A twist on the candle mystery teach article.

Author(s): Steven Ka Kit Yu

Three candles of different heights are lit in a closed space. Surprisingly, the longest candle goes out first. Can you solve the mystery?

In a classic demonstration of the candle mystery, three lit candles of different heights are covered with a gas jar (see figure 1) and the tallest candle goes out first. This happens because carbon dioxide produced from burning has a higher temperature, so it rises and accumulates at the top of the jar. Then the carbon dioxide gas cools down, falls, and extinguishes the tallest candle first. This article builds on the classic demonstration of the candle mystery and advances it in three ways. Firstly, the 5E instructional model [ 1 ] is used to develop learning activities that require students to construct, revise, and apply scientific explanations in unpredictable contexts. Secondly, these activities aim to help students test their hypotheses by using and coordinating multiple pieces of evidence. Thirdly, these activities include experiments and discussion tasks to challenge students to predict and explain results. By adding variables to the candle mystery, you can engage students and promote critical thinking and scientific understanding.

The experiments can be conducted as demonstrations or as hands-on practical work for small groups of students. They are quick and easy. The activities can be used with students aged 11 to 16.

Safety notes

• Follow all fire safety regulations and have fire extinguishing materials on hand.
• Wear safety goggles throughout the experiments. If students are performing any steps themselves, they should do the same and be warned to take care around open flames.
• The gas jar can become very hot during and immediately after candles are extinguished. Students should be warned not to touch it with bare hands and care should be taken (e.g., wear heat-resistant gloves when lifting the hot gas jar and/or lift the gas jar when it has cooled to room temperature).
• Make sure all candles are extinguished after each experiment.
• Ensure sufficient ventilation, for example, by opening windows.

Activity 1: Engaging and exploring student ideas for the candle mystery

This activity aims to set up a scenario to engage students in inquiry. When three candles of different heights are lit and covered with a gas jar, students are prompted to predict and explain which candle they think will go out first. Allow 40 minutes for the prediction discussion, experiments, and collaboration.

• Large gas jar (large enough to cover three candles)
• Three candles of different heights
• Heat-proof mat
• Hot-air gun, 240 V, 2000 W (optional: used to heat the blade to cut candles to different heights)

Worksheet 1

Preparation

Before the lesson, the setup should be prepared by the teacher or teaching assistant.

• Cut three candles to different lengths with a hot blade preheated by a hot-air gun (see figure 2).

• Align the three candles on a heat-proof mat, close enough that they can be covered with the gas jar.
• Cover the three candles with the gas jar (without lighting them, figure 3).

Practical tips :

• To ensure fair testing and expected results, ensure that the wicks are identical in length, and that the heights of the candles differ significantly.
• Perform a test run before the lesson to check that the setup works and to get a sense of how long it takes for the first candle to go out.
• Show the setup to students and encourage them to think about what would happen if we lit the candles (and replaced the gas jar). Ask them which candle they expect to go out first.
• Have them write down their own ideas first (and record them in worksheet 1) and then optionally have them discuss this in groups and then with the class. Ask them which candle they expect to go out first.
• Remove the jar, light the candles, and watch what happens. Depending on the setup (e.g., candle length, jar size), the candles should go out within a few minutes. Students often find the result (the tallest candle goes out first) mind-blowing.

• Optional: have students repeat the experiment (or watch a recording) and record the times required for each candle to go out. Combine the results and draw a graph.
• Discuss the results and encourage students to reflect on their initial predictions. Were students surprised by the results? Did the results match their predictions? Does it make them think differently about their explanation?
• A more in-depth discussion about why the tallest candle goes out first follows in Activity 2. If Activity 2 is not being used, part 1 (Why does the tallest candle go out first?) of Activity 2 can be carried out here.

Watch a demonstration of Activity 1.

You can adopt the think–pair–share approach to engage with student thinking in step 1. In this approach, students are asked to predict and explain individually which candle would go out first. They then share their predictions and explanations in groups of three or four, followed by a whole-class discussion. You can capture students’ initial ideas and reasoning and stimulate students’ thinking using the following questions:

• Why do you think the tallest or shortest candle goes out first, or why do you think the candles go out at similar times?
• After listening to your classmates’ ideas, would you change your prediction?
• How would you convince others that your prediction is correct?

Activity 2: Explaining the candle mystery

Instead of explaining to students that hot carbon dioxide rises to the top of the jar and extinguishes the tallest candle first, a discussion to help them think it through themselves will lead to better understanding. It is important to allocate time and support for students to reflect thoughtfully. They can test the explanation by monitoring changes in carbon dioxide concentration [ 2 ] and the temperature inside the gas jar. The activity takes about 40 minutes.

• Three plastic bottle caps
• Adhesive putty like Blu Tack or some adhesive tape
• Bicarbonate indicator solution (10 ml)
• Three temperature sensors (e.g., PASPORT chemistry sensor)

Evidence cards

Worksheet 2

• Timer (optional)

Part 1: Why does the tallest candle go out first?

• Ask students why they think the tallest candle goes out first. If they mention CO 2 , you can prompt them to think about how to test their hypotheses.
• Why did the candles go out before they burned down?
• How does the air in the jar change as the candle burns?
• What chemical process creates flames? What are the outputs of combustion?
• What happens to gases when they’re heated?

You can also link this to the real-life situation of escaping from fires by asking questions like:

• What are the essential actions to be followed in case of a fire inside a building?
• Why do we stay low to crawl through smoke-filled rooms or corridors?
• You can use the evidence cards (figure 4) to help guide the discussion.
• Once they have some ideas involving CO 2 build-up and temperature differences, ask how they would test their hypotheses. Encourage them to think about what variables would need to be kept the same to ensure a fair test.
• The experiments in parts 2 and 3 can be used to investigate some of these variables, or you can come up with your own.

Part 2: Monitor the carbon dioxide concentration

Safety note

A safe distance between the flame and Blu Tack/tape should be maintained to avoid melting of the Blu Tack/tape.

• Set up the experiment as for Activity 1. You can use the same candles but ensure the wicks are the same lengths.
• Fill three plastic bottle caps with bicarbonate indicator and use Blu Tack or tape to stick them at different levels inside the gas jar (figure 5).
• Repeat the procedure detailed in Activity 1, and observe colour changes to the bicarbonate indicators at the end of the experiment (figure 6).

Practical tip

To ensure fair testing, the amounts of bicarbonate indicator added to the bottle caps need to be the same.

Watch a demonstration of Activity 2a.

Part 3: Monitor the change of temperature

• Calibrate the temperature sensors if necessary.
• Set up the experiment as for Activity 1. You can use the same candles but ensure the wicks are the same lengths and the glass jar is replaced to ensure the experiment starts at room temperature.
• Connect three temperature sensors and use Blu Tack or tape to stick the sensors at different levels inside the gas jar (figure 7).
• Repeat the procedure detailed in Activity 1, and collect data for temperature changes at different levels inside the gas jar (figure 8).

The results should show that the carbon dioxide levels and temperature rise more towards the top of the jar. Discuss with students whether these results support their explanations. Are there any alternative explanations that are consistent with the results?

Activity 3: Elaborating and evaluating student learning about the candle mystery

To assess students’ deep understanding and ability to apply their explanations, you can introduce variations of the candle experiment in different contexts. Challenge your students to consider what they think might happen if we place the candles in separate jars. [ 3 ] Additionally, ask them to explore the results if we introduce an electric fan into the setup. This can be combined with another think–pair–share activity to promote discussion and evaluate their understanding of the concepts. Allow 40 minutes for the experiments and discussion.

• Portable fan

Worksheet 3

• Activity 3 explanation

Part 1: Burning candles in individual beakers

• Ask the students what they think would happen if the candles were lit in individual jars. This can be done using the think–pair–share approach.
• Secure three candles of different heights to the bench (this also works with two candles).
• Light the candles and cover each with a separate beaker (figure 9).
• Record the time required for each candle to go out.
• Repeat the experiment to get more reliable data.

To ensure fair testing, the volume inside the beaker must remain the same throughout the experiment. If a candle needs to be cut, the cut pieces should be placed inside the beaker.

Watch a demonstration of Activity 3a.

Part 2: Burning candles near a small fan

• Ask the students what they think would happen if a fan were placed in the jar. Place a portable fan near the three candles used in Activities 1 and 2, and turn the fan on.
• Repeat the procedure detailed in Activity 1, and record the time that the candle goes out.
• Repeat the experiment with the fan turned off.
• Compare the time taken for the candle to go out when the fan is on and off.

Practical tips

• To ensure fair testing, the volume inside the beaker must remain the same throughout the experiment. The electric fan should be placed inside the beaker, whether it is turned on or off.
• To repeat the experiment, you may fan the gas jar to restore it to room temperature and avoid the build-up of CO 2 , or you can use a new gas jar.

Watch a demonstration of Activity 3b.

The candles go out at similar times in the experimental setups with separate beakers or with an additional electric fan. The results contrast the experimental results in Activities 1 and 2. To ensure reliability of the results, students are encouraged to repeat their experiments, which can be performed within 5 minutes. Encourage students to provide explanations for their observations. Students are asked to construct explanations of how and why things happen in the setup using their explanations developed in Activity 2. You may give groups the model answer ( Activity 3 explanation ) at the end to compare it to their descriptions.

The activities based on simple twists to the classic candle experiment can serve to improve students’ abilities to develop, revise, and apply scientific explanations, as well as to explore scientific skills such as control of variables, hypothesis testing, and coordinating multiple pieces of evidence. As an extension activity, you could encourage students to handle quantitative data in an in-depth discussion and demonstrate their learning through report writing and group presentation. The process of predicting and explaining different unfamiliar contexts can help create valuable teachable moments that motivate students to learn.

[1] Bybee RW (2015) The BSCS 5E Instructional Model: Creating Teachable Moments . National Science Teachers Association Press. ISBN-10: 194131600X

[2] Cheng MW (2006) Learning from students’ performance in chemistry-related questions. In Yung BHW (ed.) Learning from TIMSS: Implications for Teaching and Learning Science at the Junior Secondary Level pp 51–74. Education and Manpower Bureau.

[3] Details for how to investigate candle burning: https://edu.rsc.org/resources/candle-burning-investigation-planning-an-experiment/619.article

• Watch demonstration videos of the experiments in Activities 1 ( candle mystery ), 2 ( CO 2 concentration ), and 3 ( individual beakers and electric fan ).
• Learn how to make convection currents visible using mist: Lim ZH, Shu A, Ng YH (2023) A misty way to see convection currents . Science in School 64 .
• Explore the nature of science by investigating a mystery box without peeking inside: Kranjc Horvat A et al. (2022) The mystery box challenge: explore the nature of science . Science in School 59 .
• Try some experiments with gases to illustrate stoichiometric reactions and combustion: Paternotte I, Wilock P (2022) Playing with fire: stoichiometric reactions and gas combustion . Science in School 59 .
• Learn about data visualization by sketching graphs from ‘story’ videos of everyday events: Reuterswärd E (2022) Graphing stories . Science in School 58 .
• Read about the environmental costs of fireworks: Le Guillou I (2021) The dark side of fireworks . Science in School 55 .

Steven Ka Kit Yu has been working in the education sector in teaching, research, and administrative roles. He was a secondary science teacher and a part-time lecturer in the Faculty of Education, the University of Hong Kong.

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Activity 3 Explanation

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Rising water experiment

Follow FizzicsEd 150 Science Experiments:

You will need

• A clear glass cup that is taller than the candle
• Adult supervision

• Instruction

Using the playdough, fix the candle to the bowl so that it sits upright inside the bowl.

Pour some water into the bowl.

With the matches, light the candle.

Cover the candle with the glass cup. Watch what happens! If you want, you can add food colouring into the water to make the experiment more visible.

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What is happening?

You created an area of low pressure!

When the experiment is run you can see tiny bubbles escaping under the glass which shows that the air pressure increased inside the glass from the heated air as the candle burns. Once the candle runs out of oxygen, the candle burns out and the remaining air inside cools down. Cooling air contracts ( see liquid nitrogen on a balloon! ) which lowers the air pressure inside the glass. This created a pressure difference between the air inside the glass and the air outside the glass. This pressure difference caused the high-pressure air outside the glass to push the water down into the plate… allowing the water to be pushed upwards into the inside of the glass towards the lower-pressure air inside the glass.

Variables to test

More on variables here

• hot vs. cold water
• Two candles vs. one candle
• What happens when you use different liquids?

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6 thoughts on “ Rising water experiment ”

Hi When I was at school 30 years ago the oxygen use causing the rise was taught. Since then, it is my understanding from lots of reading, that the reasons behind the rise are related more to temperature as described nicely by Steve Spangler below.

A common misconception is that the consumption of oxygen by the flame in the container is a factor in the water rising. There may be a slight possibility that there would be a tiny rise in the water from the flame using up oxygen but it’s extremely small compared to the actual reason. Simply put, the water would rise imperceptibly at a steady rate as the oxygen were consumed. You likely saw the level rise almost all at once and pretty much after the flame went out.

At first, the flame heats the air inside the container and this hot air expands quickly. Some of the expanding air escapes from under the vase where you might have seen some bubbles. When the flame fades and goes out, the air in the container cools and cooler air contracts or takes up less space. That contraction creates a weak vacuum – or lower pressure – in the container. Where’s the higher pressure? Right! It’s outside the container pressing down on the water in the dish. The outside air pushes water into the container until the pressure is equalized inside and outside the container. The water stops rising when that pressure equalization is reached. https://www.stevespanglerscience.com/lab/experiments/why-does-the-water-rise/

Hi Angela, You’re right and great spot! It looks like this explanation missed the other half of the answer and it’s been updated now. Thanks for the heads up!

Thanks a lot !!! You saved me …? Tmrw was my science test and I was desparatly searching for this answer …

Great experiment to try i tried it and it failed ):

Oh no! How did you set your experiment up? Usually, the failure happens when the water on plate isn’t high enough. Give it a go again!

Yeah I will(:

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Burning Candle Rising Water Experiment

• December 3, 2020
• 5-6 Year Olds , 7-9 Year Olds , Chemistry , Fire Science , Physics , Rainy Day Science

In our previous experiment , we discussed the candle covered with glass. The basic science behind was the oxygen limitation that made the candle go off.

In an extension of that science activity, I am now going to share another experiment with you. It is also to do with candles and glass, but with a twist.

Apart from the oxygen limitation that puts the candle off, there is also low pressure created in the glass that leads to a vacuum.

This will cause some effects and that looks like magic to kids but the science to all adults. So let us do this magic to our kids and also explain them some science.

Things required

• Ceramic or glass plates
• Glass tumbler
• Matchbox with stick

Steps involved

Fill the plate with water.

Place the candle on the plate and lit it. You can see the candle glowing brightly.

It may float or stand on the water in the plate based on the weight of the candle.

The presence of water does not make any difference to the candle at this stage.

After sometime invert the glass tumbler and place it on the glowing candle.

Imagine the glass will close the candle. In a few minutes, you can witness candle blowing off as the closed glass limits oxygen in the space surrounding the candle.

Another thing you will witness is now the water in the plate enters the glass and you will see the level rising constantly.

Science Behind Candle Rising Water

The basic science here is the lack of oxygen puts off the candle in step 2. At the same time lack of oxygen also lowers the atmospheric pressure and creates a vacuum.

This leads to the water entering the glass from the plate. You can see this like the water level rises in the glass.

Detailed science with chemical equations

The water level rises to 1/10th of the glass before the candles go off is importantly you must note.

There is no air bubble formed. The water level will stay for few minutes once the candle goes off completely.

So both the candle dies out and water rises happens concurrently.

Chemical equation

Oxygen + Candle (wax/paraffin) à Water and Carbon dioxide

O 2 + C n H 2n+2 à H 2 O + CO 2

I have an exercise for older kids here. Yes, ask your older kids to balance the chemical equation taking n as 1. Post the answers for learning.

The oxygen is 2 times more than the carbon dioxide released and hence the air volume reduces.

Let me also explain the physics behind this experiment for physics fans!

Physics facts

The burning candle produces heat which heats the air and thus expansion happens. This will cancel the oxygen depletion slowly and the water level remains down.

When oxygen gets saturated in the glass the candle goes off and the air begins to cool and volume decreases.

The reduction in air pressure will create a vacuum and hence water level rises.

Also, water initially is in the gas state when there is heat around and later it condenses and rises in level as water.

The same process or science is applied to how storms and hurricanes are formed.

When the sun heats up the air causing its density become low which is the reason for formation of wind and storms.

The high density air moves into the lower density air pockets. When there is enough wind referred to as ‘hurricanes’ causing the water rise and lifted up out of the ocean.

• This experiment is magic for kids aged 3 to 5.
• You can teach some science to kids 5 – 8 as they will know about oxygen etc.
• 8 -12-year-old kids can benefit from the chemical equations and the detailed science of this experiment.

As I always alert you, please make sure to assist or monitor kids when they do this experiment.

It involves fire and you must be around to avoid any accident. Also, dealing with glass dishes needs support which you must provide.

Depending on the age of your kid you decide whether you must take their help or help them or just be around. However, we advise you to be present irrespective of the kid’s age.

Interested in More Air Pressure Experiments? Explore the list below

DIY Drip Drop Water Bottle

Balloon Powered Car

Make a Balloon Rocket

We have tried answering a few usual questions that might arise in the kid’s mind. My little one always ask questions upon which I fumble many times. So here you go with ready-made answers as well.

Twice the time of oxygen is burnt than the available CO2 that decreases the air pressure and hence water level rises. The air cools soon after flames go off and the molecules slow down making the water vapor condense to moisture.

The heat of the flame will start melting the wax near the wick and the liquid wax is drawn up to the wick due to capillary action. The flames heat will vaporize the wax and break them into molecules of oxygen and carbon.

The candle is put off by placing the lid on the candle that is lit. It is another way to extinguish the candle. The lid is placed on the flame which immediately cuts off the oxygen and thus puts off the candle.

The wick gets close to the glass the wax burns off and heats the glass. This might lead to the explosion of the glass. However, when water is kept on the glass this explosion is prevented.

As long as the pressure is low the water rises and when the pressure level equalizes the water level stops rising.

Place the glass flat on the plate to prevent air bubble forming. In case if it is tilted, then the air bubbles will form due to the difference in the pressure level between the inside and outside surface.

When you observe the tall and short burning candles closed with a glass container, surprisingly the tall candle goes out first because the carbon dioxide released travels upwards and suffocates the tall candle making the cold air sink. The short candle utilizes the oxygen in this cold air and stays on for some more time. When all the oxygen is used up, the short candle also dies.

Yes, place a candle in the bowl containing water and lit it. Slowly it goes down melting the wax which forms a protected wax around the wick. This allows the candle to stay on for good amount of time even though the flame has reached the level lower than the water. And of course, after a while water gets into wick and turns the flame off.

Modifications you can try with this experiment

 Here are the few variations to further explore the scientific concepts in this experiment.

• Change the amount of water taken in the plate and observe how does it affects the water level rise.
• Discuss on what happened to the water when the candle is lit.
• How does temperature changes happen when we use different types of colored water?
• You can use colored water made of food coloring, milo, liquid dyes, powdered dye etc.
• Experiment on hot water versus cold water and observe the temperature and air pressure changes.
•  Also try the experiment using two candles versus one candle or more candles etc.
• Use different liquids instead of water and check what are the changes and results.
• Try with different candle weight and height
• Change the glass to narrow and broad
• Make colored water and also increase/lower the water level in the plate
• Try not to lit a candle before and light it only after placing the glass. Yes, you need to lift it a bit and light it. Preheating is avoided to observe for any changes in the results.

Share the results with us that will let all our readers know what happens with all these modifications. In the meantime, I will also try different twists with my kids and post my experience.

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Rising Water Experiment

Light a fire under middle school science and heat it up! Place a burning candle in the water and watch what happens to the water. Explore how heat affects air pressure for an awesome middle school science experiment. This candle and rising water experiment is a great way to get the kiddos thinking about what is happening. We love  simple science experiment s; this one is super fun and easy!

Candle in Water

This candle experiment is a great way to excite your kiddos about science! Who doesn’t love watching a candle? Remember, adult supervision is required, though! We love  simple science experiment s; this one is super fun and easy!

This science experiment asks a few questions:

• How is the candle flame affected by placing a jar over the candle?
• What happens to the air pressure inside the jar when the candle goes out?

💡 Make sure to check out all our chemistry experiments and physics experiments !

Click here to get your free printable STEM activities pack!

Candle in a Jar Experiment

You need to change one variable if you want to extend this science experiment or use the  scientific method  for a science fair project .

EXTEND THE LEARNING: You could repeat the experiment with candles or jars of different sizes and observe the changes.

💡Learn more about the scientific method for kids here .

• Middle School Science
• Elementary Grades Science
• Tea light candle
• Bowl of water
• Food coloring (optional)

Instructions:

STEP 1: Put about a half inch of water into a bowl or tray. Add food coloring to your water if you like.

STEP 2: Set a tea candle in the water and light it.

ADULT IS SUPERVISION REQUIRED!

STEP 3: Cover the candle with a glass, setting it in the bowl of water.

Now watch what happens! Do you notice what happens to the level of water under the jar?

Why Does the Water Rise?

Did you notice what happened to the candle and the water level? What’s happening?

The burning candle raises the air temperature under the jar, and it expands. The candle flame uses up all of the oxygen in the glass, and the candle goes out.

The air cools because the candle has gone out. This creates a vacuum that sucks up the water from the outside of the glass.

It then raises the candle up on the water that enters the inside of the glass.

What happens when you remove the jar or glass? Did you hear a pop or popping sound? You most likely listened to this because the air pressure created a vacuum seal, and by lifting the jar, you broke the seal, resulting in the pop!

More Fun Science Experiments

Why not also try one of these easy science experiments below?

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Experimental Design - Independent, Dependent, and Controlled Variables

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Scientific experiments are meant to show cause and effect of a phenomena (relationships in nature).  The “ variables ” are any factor, trait, or condition that can be changed in the experiment and that can have an effect on the outcome of the experiment.

An experiment can have three kinds of variables: i ndependent, dependent, and controlled .

• The independent variable is one single factor that is changed by the scientist followed by observation to watch for changes. It is important that there is just one independent variable, so that results are not confusing.
• The dependent variable is the factor that changes as a result of the change to the independent variable.
• The controlled variables (or constant variables) are factors that the scientist wants to remain constant if the experiment is to show accurate results. To be able to measure results, each of the variables must be able to be measured.

For example, let’s design an experiment with two plants sitting in the sun side by side. The controlled variables (or constants) are that at the beginning of the experiment, the plants are the same size, get the same amount of sunlight, experience the same ambient temperature and are in the same amount and consistency of soil (the weight of the soil and container should be measured before the plants are added). The independent variable is that one plant is getting watered (1 cup of water) every day and one plant is getting watered (1 cup of water) once a week. The dependent variables are the changes in the two plants that the scientist observes over time.

Can you describe the dependent variable that may result from this experiment? After four weeks, the dependent variable may be that one plant is taller, heavier and more developed than the other. These results can be recorded and graphed by measuring and comparing both plants’ height, weight (removing the weight of the soil and container recorded beforehand) and a comparison of observable foliage.

Using What You Learned: Design another experiment using the two plants, but change the independent variable. Can you describe the dependent variable that may result from this new experiment?

Think of another simple experiment and name the independent, dependent, and controlled variables. Use the graphic organizer included in the PDF below to organize your experiment's variables.

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Categories STEM Activities

Rising Water Experiment – Magic Water Science Experiment

Rising Water Experiment: a magic rising water science experiment.

• Ages: Preschool , PreK , Kindergarten, Elementary
• Difficulty: Easy
• Learning: STEM , Air Pressure, Ideal Gas Law, Charles’s Law

Did you know you can make water rise without touching it?

Nope, it isn’t magic. It’s science. Surprisingly simple science in fact. This science experiment comes together in minutes, but it will captivate your children.

Here is how to do the raising water experiment, simple glass and candle STEM magic.

What's In This Post?

Supplies for your Glass and Candle Experiment

How to do the rising water experiment, the science, the chemical component, the physical component, the big picture, what should children take away from this science experiment, conservation of matter, charles’s law, ideal gas law, ask a question, magic water science experiment, free printable raising water experiment instructions, instructions, rising water experiment.

This experiment uses at-home materials and is fascinating! It does require adult help, but adults will love it too.

You only need a few items to make this magic water STEM experiment work. Here is what you need to gather up:

• Glass or Jar
• Small Votive Candle
• Shallow Dish
• Food Coloring (Optional)
• Matches or Lighter

Before we even get started please remember that an adult needs to be present for this experiment. We are using fire, which can be dangerous, so be smart.

Step 1: Take a sallow dish and fill it with water. You want just enough to cover the bottom.

Step 2: If you want, add food coloring to the water. This just makes it easier to see and is fun, so totally optional.

Step 3: Place your small votive in the middle of the dish.

Step 4: Light the candle, then quickly place the empty glass over the flame, touching the water. Now wait while the candle burns out.

Step 5: Watch as the water rises up into the glass!

The number one safety tip here is to be careful with the flame! This experiment must be done with adult supervision at the bare minimum. With younger children, like preschoolers, this needs to be an adult-led experiment.

This STEM activity also uses glass, so it is a good idea to be careful in case it falls or breaks.

Clean-up for this activity is pretty simple. Slowly lift the bottle off of the candle.

Once the bottle is off, gently blow the candle out. Let the candle cool (or have an adult get it), remove it from the dish, and dump the water down the drain. That’s it!

More must do activities!

How the Rising Water Experiment Works

This is a pretty cool experiment, but it is important to talk about what actually makes this happen. It’s fun to say it is magic, but as my kids tell me, ‘It’s better. It’s science.’

There are two main components of this experiment that cause the water to rise, a physical component and a chemical component. These two components work together to make this experiment happen.

The candle burning creates a chemical reaction. The flame burns both the paraffin (candle wax) and the oxygen under the glass. This reaction uses up oxygen and creates water and carbon dioxide as a result. Twice as much oxygen is burned than carbon dioxide produced, so the volume of air in the glass decreases.

(Note the total amount of matter in the jar remains the same. Conservation of matter tells us this. But some molecules are larger than others and take up more space in terms of volume.)

The physical component is why the water level in the glass doesn’t rise as soon as the candle is covered. The candle warms the air, and this increases the air volume inside the glass.

When the candle burns out (because all the oxygen is used up), the temperature cools quickly. This temperature decrease means the volume also decreases, which lets the water rise to fill up that space. This is called Charles’s Law.

Charles’s Law tells us that the ratio of volume to temperature must remain the same, so if one goes down the other goes down too.

These two parts of the experiment work together. Both the volume change and temperature also affect the pressure in the system we created. When temperature decreases (the physical component) and the size of the matter decreases (the chemical component), the pressure of the gas inside the glass decreases too.

This lower pressure inside means the water can rise as well. This is explained by the Ideal Gas Law.

The idea of air pressure can be a bit challenging for young children to understand. It isn’t something they can clearly see, so that makes sense. But they can understand something changing size, in other words when volume changes.

If the air inside the glass takes up less space, it makes sense for the water to fill in that space and rise inside the glass.

I understand that we went over a lot of more complicated concepts here. (And don’t worry, I’ve listed the definitions for the terms below to help out.) Am I really expecting young kids to understand and retain all this?

No. I mean, it would be cool if they did. And some might. But realistically that is not the point of this kind of science. The purpose of giving these explanations is so that you as a caregiver can quickly get the reasoning behind this project and interpret it for your children.

It is helpful for your children to see these experiments. Even if they don’t fully understand the details, this experience is adding to their understanding of how the world around them works. It builds their science base.

Using the vocabulary helps kids as well. First, it gives new words which are always helpful for communication skills. But I think, more importantly, it demystifies science later in life. Science can feel like a whole new language as we get older, and that can be very intimidating. If we have been exposed to these terms though, it’s less scary. We might not know exactly what they mean but we know that we have heard them before. This helps kids feel like science belongs to them. Because it does.

Helpful Definitions

Here are a few helpful definitions for the raising water experiment.

The conservation of matter law states that matter is not destroyed or created. It can change forms, but the total amount stays the same.

Charles’s Law tells us that the volume of a gas is directly proportional to the temperature of the gas. As the volume decreases, the temperature decreases, for example.

The Ideal Gas Law describes the conditions a gas is under and how those conditions will vary as compared to each other. The pressure of the gas multiplied by the volume will always equal the number of moles multiplied by the temperature and ideal gas law constant.

The Scientific Method

Since an adult is needed to run do this experiment with kids (fire safety!), it is a great time to talk through the scientific method! Here is a guideline of what that can look like with this STEM experiment.

(And don’t forget to learn all the life lessons that come along with the scientific method here: Beyond the Science- What Kids Are Really Learning .)

Ask your child, what do they think is going to happen when we put the glass on the candle? The key here is to listen and let them think it through. No answer is too far out there or wrong at this step.

The observation step is key throughout any experiment, but take a moment and look at their components. What do they notice about them? How do they normally behave? What do they already know about them?

Narrow down your potential answers and decide on one or a couple of outcomes you think are most likely. This is your hypothesis.

Time to run the experiment! Encourage your children to keep watching what is happening. (In this particular observation, sight is going to be the key thing to focus on. Some touch is possible, watching out for the flame of course. And you can encourage smell and hearing for practice.

What did they observe? Now is the time for them to tell you everything they can about what just happened.

This is where we form the conclusions and apply the information we learned. Do they think this will always happen? How did the results match or differ from their hypothesis?

Real experiments always lead to more questions. What does your child want to try next? What would they change in the experiment? Does more water in the dish change anything? Can they try to suck up all the water? Would adding a different liquid change the results?

Even if you aren’t able to complete any of their additional experiment ideas, it is a good idea to think of ways to explore more. Plus it is amazingly fun to hear all the ideas kids have.

This is a great experiment to do over and over. It’s fast, cheap and full of fun learning. It’s a must-do!

Let’s find your next fun activity!

Raising Water Experiment

How to do the raising water experiment that will wow kids!

• Food Coloring (optional)
• Lighter or Matches
• Fill your shallow dish with enough water to cover the bottom. Add food coloring. (optional)
• Place your votive in the middle of the dish.
• Light the votive candle.
• Place the glass upside down over the candle.
• Wait for the candle to burn out and watch the water rise!

This is a science experiment that needs adult supervision and help. It uses fire and needs an adult to be safe.

To clean up, gently pull the glass off the candle. Make sure the candle cools and the water can go down the drain.

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Independent and Dependent Variables Examples

The independent and dependent variables are key to any scientific experiment, but how do you tell them apart? Here are the definitions of independent and dependent variables, examples of each type, and tips for telling them apart and graphing them.

Independent Variable

The independent variable is the factor the researcher changes or controls in an experiment. It is called independent because it does not depend on any other variable. The independent variable may be called the “controlled variable” because it is the one that is changed or controlled. This is different from the “ control variable ,” which is variable that is held constant so it won’t influence the outcome of the experiment.

Dependent Variable

The dependent variable is the factor that changes in response to the independent variable. It is the variable that you measure in an experiment. The dependent variable may be called the “responding variable.”

Examples of Independent and Dependent Variables

Here are several examples of independent and dependent variables in experiments:

• In a study to determine whether how long a student sleeps affects test scores, the independent variable is the length of time spent sleeping while the dependent variable is the test score.
• You want to know which brand of fertilizer is best for your plants. The brand of fertilizer is the independent variable. The health of the plants (height, amount and size of flowers and fruit, color) is the dependent variable.
• You want to compare brands of paper towels, to see which holds the most liquid. The independent variable is the brand of paper towel. The dependent variable is the volume of liquid absorbed by the paper towel.
• You suspect the amount of television a person watches is related to their age. Age is the independent variable. How many minutes or hours of television a person watches is the dependent variable.
• You think rising sea temperatures might affect the amount of algae in the water. The water temperature is the independent variable. The mass of algae is the dependent variable.
• In an experiment to determine how far people can see into the infrared part of the spectrum, the wavelength of light is the independent variable and whether the light is observed is the dependent variable.
• If you want to know whether caffeine affects your appetite, the presence/absence or amount of caffeine is the independent variable. Appetite is the dependent variable.
• You want to know which brand of microwave popcorn pops the best. The brand of popcorn is the independent variable. The number of popped kernels is the dependent variable. Of course, you could also measure the number of unpopped kernels instead.
• You want to determine whether a chemical is essential for rat nutrition, so you design an experiment. The presence/absence of the chemical is the independent variable. The health of the rat (whether it lives and reproduces) is the dependent variable. A follow-up experiment might determine how much of the chemical is needed. Here, the amount of chemical is the independent variable and the rat health is the dependent variable.

How to Tell the Independent and Dependent Variable Apart

If you’re having trouble identifying the independent and dependent variable, here are a few ways to tell them apart. First, remember the dependent variable depends on the independent variable. It helps to write out the variables as an if-then or cause-and-effect sentence that shows the independent variable causes an effect on the dependent variable. If you mix up the variables, the sentence won’t make sense. Example : The amount of eat (independent variable) affects how much you weigh (dependent variable).

This makes sense, but if you write the sentence the other way, you can tell it’s incorrect: Example : How much you weigh affects how much you eat. (Well, it could make sense, but you can see it’s an entirely different experiment.) If-then statements also work: Example : If you change the color of light (independent variable), then it affects plant growth (dependent variable). Switching the variables makes no sense: Example : If plant growth rate changes, then it affects the color of light. Sometimes you don’t control either variable, like when you gather data to see if there is a relationship between two factors. This can make identifying the variables a bit trickier, but establishing a logical cause and effect relationship helps: Example : If you increase age (independent variable), then average salary increases (dependent variable). If you switch them, the statement doesn’t make sense: Example : If you increase salary, then age increases.

How to Graph Independent and Dependent Variables

Plot or graph independent and dependent variables using the standard method. The independent variable is the x-axis, while the dependent variable is the y-axis. Remember the acronym DRY MIX to keep the variables straight: D = Dependent variable R = Responding variable/ Y = Graph on the y-axis or vertical axis M = Manipulated variable I = Independent variable X = Graph on the x-axis or horizontal axis

• Babbie, Earl R. (2009). The Practice of Social Research (12th ed.) Wadsworth Publishing. ISBN 0-495-59841-0.
• di Francia, G. Toraldo (1981). The Investigation of the Physical World . Cambridge University Press. ISBN 978-0-521-29925-1.
• Gauch, Hugh G. Jr. (2003). Scientific Method in Practice . Cambridge University Press. ISBN 978-0-521-01708-4.
• Popper, Karl R. (2003). Conjectures and Refutations: The Growth of Scientific Knowledge . Routledge. ISBN 0-415-28594-1.

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