experiment to show convection in gases

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Convection Science Experiment – How Heat Moves through Liquid

Can heat cause movement? With a few drops of food coloring, cooking oil, and a candle you can find out! In this simple yet exciting science experiment, kids can explore the concepts of density and convection as they watch convection currents in motion!

A demonstration video, printable instructions, and a supplies list are included as well as an easy to understand scientific explanation of how this experiment works.

Note: Because this experiment uses a fire component, adult supervision is required.

JUMP TO SECTION:   Instructions  |  Video Tutorial  |  How it Works | Purchase Lab Kit

Supplies Needed

• Large heat safe glass bowl
• Cooking Oil
• Food Coloring
• Two 2×4 blocks
• Match or Lighter

Convection Science Lab Kit – Only $5

Use our easy Convection Science Lab Kit to grab your students’ attention without the stress of planning!

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Convection Science Experiment Instructions

Step 1 – Begin by filling a large glass bowl with cooking oil.

Step 2 – Next, add between 5-10 drops of food coloring into the oil. Take a moment to make some observations. What happens to the food coloring? Does it mix with the oil?

Helpful Tip: Place the drops near the center of the bowl.

Step 3 – Prop the bowl up off the table using two 2×4 blocks. Position the blocks so there is a space between them to put a candle.

Step 4 – Light a candle and carefully place it under the bowl. The flame of the candle should touch the bottom of the glass bowl. 

Step 5 – Look through the side of the glass bowl and watch carefully to observe what happens. Write down what happens. Helpful Tip: It will likely take 5 minutes before you see anything happen to the liquid/food coloring.

Do you know why the food coloring moves around in the oil? Find out the answer in the how does this experiment work section below.

Video Tutorial

How Does the Science Experiment Work

Heat can move in three ways: conduction, convection, and radiation. In this experiment, heat is transferred by means of convection. Convection is the transfer of heat by the movement of currents within a fluid.

In our experiment, the oil at the bottom of the bowl was heated by the candle. The particles of oil at the bottom of the pot began to move faster and further apart. As a result, these oil particles became less dense than the rest of the oil particles in the bowl, so these heated, less dense oil particles began to rise. (Less dense fluids rise and more dense fluids sink). The surrounding, cooler oil particles flow in to take its place. This flow creates a circular motion known as a convection current . A convection current is caused by the rising and sinking of heated and cooled fluids.

You can see evidence of the convection current if you look at the food coloring in the bowl. Notice bubbles of food coloring rise from the center of the bowl, drift to edges of the bowl, and sink back to the bottom.

Convection currents are all around us and responsible for heating many things! Our homes are heated in the winter through convection currents. The troposphere of the atmosphere (the layer closest to Earth) is heated through convection currents. The mantle inside of Earth is heated through convection currents, which causes Earth’s crust to drift in a process called continental drift.

I hope you enjoyed the experiment. Here are some printable instructions:

Convection Science Experiment

• Two 2×4 blocks

Instructions

• Begin by filling a large glass bowl with cooking oil.
• Next, add between 5-10 drops of food coloring into the oil. Helpful Tip: Place the drops near the center of the bowl.
• Prop the bowl up off the table using two 2×4 blocks.
• Light a candle and carefully place it under the bowl. The flame of the candle should touch the bottom of the glass bowl.
• Look through the side of the glass bowl and watch carefully to observe what happens. Helpful Tip: It will likely take 5 minutes before you see anything happen to the liquid/food coloring.

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Science project, heat convection in liquids.

Energy is all about action! Thermal energy is transferred in many ways. The thermal energy of a substance can be determined by adding up all the kinetic and potential energy of its molecules. Convection is one form of energy transfer where heat energy is transferred by large scale movement in a gas or liquid. Convection currents form, which are streams of gas or liquid powered by convection. Some of this movement is caused by differences in density . You might remember that density how much matter there is in a given amount of space. In this convection current experiment for kids, you are going to make convection currents in water, which you will be able to observe with the help of food coloring.

How does the convection of water work?

• Clear quart container or jar
• Coffee mug or other container that can withstand heat
• Blue food coloring
• Fill the clear jar halfway with cold water.
• Place the jar freezer for 15 minutes.  You don’t want the water to freeze.
• Fill the coffee mug about ¼ full with hot water.
• Add 10 drops of blue food coloring to the hot water and stir.
• Remove the jar from the freezer and set it on table.  Wait until all the sloshing around from moving it has stopped.
• Fill the dropper with hot blue water.
• Lower the tip of the dropper until it is near the bottom of the large jar.
• Carefully release two drops of hot blue water onto the cold water.  Observe what happens, looking at the side and top of the jar.
• Add ten more drops, two drops at a time, observing what happens between each.
• Once you have added all the hot blue liquid drops, observe the jar for an additional five minutes.

When you squeeze of the drops of water with blue dye near the bottom of jar, most of it rises through the cold water and then continues to travel across the water’s surface.   Ripples of blue color move through the water.  A blue layer forms at the top of water in the jar.  As time goes by, some of the blue water begins to sink, and after five to ten minutes, all of the water turns a lighter shade of blue.

The hot blue water molecules had more kinetic energy than the cold water molecules. That means the blue water molecules were colliding more, and pushing each other part. This lowered the density of the blue water because fewer molecules could fit in the given volume. The less dense blue water therefore rose through the cold water and floated at the top. Those streams of blue fluid you saw were convection currents. Over time, thanks to the convection currents, the hot water mixed with the cold water, evening out the temperature overall. The blue food coloring also diffused throughout the liquid. Diffusion happens constantly. The blue food coloring molecules moved from higher concentration in the hot water and zero concentration in the clear water to create a more uniform distribution throughout the liquid, giving it an even, light blue appearance.   

Going Further

Do some research on warm and cold ocean currents. Water of different temperatures can move hundreds of miles!

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Modeling How Air Moves

In this activity, students use models to observe that air is a fluid that flows due to temperature-driven density differences.

Learning Objectives

• Students will understand that air is a fluid and behaves in ways we expect of other fluids.
• Students will understand that temperature-driven density changes will produce movement in fluids.
• Students will understand that temperature differences cause convection.

Part 1. Air is a fluid

For a class demonstration:

• Baking soda
• 1/4 c. measuring cup
• 500 ml beaker or a glass jar of similar size
• Candle (a small votive candle is ideal)
• Strip of poster board or cardboard that is about 12" by 3" (old file folders work well)

Part 2. Heat causes fluids to move

For the class:

• Pitchers or jugs of room-temperature water
• An electric teakettle, hot plate and pot, or coffee maker to heat water(Hot tap water is usually not hot enough.)

For each team of students:

• Clear plastic plant saucer or platter that is8 to 10 inches wide and at least an inch deep (Note: Do not use saucers with concentric raised rings on the inside bottom; radial ridges are okay.)
• Blue and red food coloring
• Small containers for food coloring such as small cups
• Eye dropper or pipette
• Three disposable cups used for hot beverages
• Bucket to collect used water if a sink is not available

Part 3. Temperature-driven density differences

For each team of students or for a class demonstration:

• A clear plastic shoebox-sized container
• Red food coloring
• Ice cubes made with blue food coloring and water
• Colored pencils (red and blue)
• Index cards or paper

Preparation

• Gather supplies. Note that Part 1works best as a class demonstration for safety reasons; however, Part 2 and Part 3 can be done as a class demonstration by students working in groups of 3 to 4. Only one set of materials is needed for a class demonstration.If performed in small groups, each group will need the materials listed.
• Parts 2and 3 require room temperature water. Leave water overnight or use a thermometer to ensure that the water is around68 to 72 degrees Fahrenheit.
• Prepare ice cubes made with blue food coloring and water at least a day before Part 3.

Part 1: Air is a fluid

Introduce fluids.

Make a ramp for the carbon dioxide by folding a piece of cardboard.

• Discuss the physical properties of fluids with students. Be sure to include the idea that fluids can be poured.
• Ask students "Can you name a fluid?" (Students will likely name liquids like water, milk, and soda.)
• Provide more detail about fluids. Tell students that a fluid is anything that would spill or float away if it weren't in a container. If you can stir it up with a spoon or blow it through a straw, it's a fluid.
• Relying on students' prior understanding of solids, liquids, and gases, ask students whether solids are fluids (generally, they are not). Ask students whether gases are fluids (which is the focus of this activity).
• Explain that, in this demonstration, students will observe whether it's possible to ‘pour’ a gas like a fluid.
• Tells students that this demonstration uses carbon dioxide gas. Because it is denser than air, carbon dioxide should flow down a ramp if it is a fluid. Show students the poster board or cardboard folded lengthwise, which is the ramp (see illustration at right).
• Put about a tablespoon of baking soda in the glass jar or beaker and add approximately 1/4 cup of vinegar. Instruct students to observe the bubbles in the jar. Explain that the vinegar and baking soda are reacting, which is filling the jar with carbon dioxide gas. Note that the carbon dioxide gas is invisible.
• Tell students that carbon dioxide gas, without any oxygen present, will extinguish a fire.(That's why carbon dioxide is used in fire extinguishers.)
• Light a match and hold it in the jar. The flame should go out. (You may need to tip the jar a bit to get the match into the carbon dioxide without burning your finger.)

Do the experiment and observe the results.  

When the fizzing subsides, hold the ramp at an angle so that one end is near the candle flame and the other end is slightly higher. Take care to keep the cardboard ramp out of the flame.

• Empty the jar and set up the experiment (as shown in the illustration at the right) with a lit candle below the ramp and the jar at the upper end of the ramp.
• Explain to students that you will again make carbon dioxide in the jar, but this time you will "pour" it down the ramp and see if it will extinguish the candle.
• Add a tablespoon of baking soda and a 1/4 cup of vinegar to the jar. When the fizzing subsides, hold the ramp at an angle so that one end is near the candle flame and the other end is slightly higher.
• "Pour" the gas from the beaker or jar down the funnel. The flame will go out in a second or two.
• Have students explain how the flame was extinguished. (Answer:There was no more oxygen available for the flame, so the flame went out. Pure carbon dioxide, which is a gas, is denser than air, so it flows like a liquid from the jar or beaker along the ramp. Since the carbon dioxide molecules are heavier, these molecules force out the oxygen molecules. The fire cannot continue without oxygen.

Part 2: Heat causes fluids to move

• Tell the class that they will conduct an experiment to observe how air moves when it's heated.
• Tell students that in this experiment water is used to simulate air in the atmosphere. Water and air move similarly because they are both fluids.
• Show students what their experiment set-up should look like (see image at right). Ask students "What do you think will happen to the food coloring when it's dropped near the heat source (cup of hot water) or when it's dropped further from the heat source?"

Place three disposable cups upside down on a piece of paper.  

Experiment set-up for Part 2

• Place the plastic plant saucer or plastic platter (here after referred to as a plate) on top of the cups. The cups should be near the outer edges of the plate and evenly spaced.
• Fill the plate three-quarters full with cool water. To make certain the water is still, let it sit before the experiment. Be careful not to bump the desk or table during the experiment.
• Using a dropper, slowly release a small amount of food coloring at the bottom of the plate of water.
• Slowly remove the dropper, taking care not to stir the water.
• Observe and draw what happens as the drop sits on the plate.
• Students should start each trial with a clean plate of water. (If your classroom doesn't have a sink, you may wish to place dump buckets around the classroom.)
• Each group will need one cup of hot water, filled almost to the top. The cup of hot water should be placed under the center of the plate.
• Ask students to draw what happens during each trial from the top view.The drawings should show the movement of the colored water and its relationship to the hot water (heat source).

Observations and Questions

• Have students write explanatory captions for the drawings they made of each trial.
• Have students repeat the exercise making drawings from the side of the plate.
• Ask students: How does heat affect the food coloring? (Answer: The dye moved more when placed near the heat source.)
• (Advanced Question) If students have learned about heat transfer, ask them to explain what type of heat transfer is taking place.( Answer:Convection is occurring because we can observe the movement of the colored water within the liquid. Convection transmits heat through the movement of molecules.)

Part 3: Temperature-driven density differences

• Introduction:
• To connect Part 2 and Part 3, discuss radiation and convection. The transfer of heat from the water in the cup to the plate in Part 2 is radiation. Convection , another method of heat transfer, is the movement of water in the plate during Part 2. (For additional information on radiation and convection, refer to the background section of this activity.)
• Show students what their experiment set up will look like for Part 3(a shoebox of water, blue ice cubes, and red food coloring). Tell students that this experiment is more like the atmosphere compared to Part 2 because there is a larger thickness/volume of fluid. Remind students that water is representing the same movement found in the air.
• Ask students "From what you have learned in Part 2, will the cold (blue) water rise or sink in comparison to the warm (red) water? Why?
• Provide each group with a plastic container 2/3 full of room temperature water.Instruct students not to move the container or table so that the water becomes completely still.
• Provide each group with a blue ice cube to put at one end of their container (alternatively, use a drop of blue coloring on ice).For best results, add the ice cube with as little disturbance to the water as possible.
• Put two drops of red food coloring at the other end of each container. (For dramatic effect, heat the red food coloring in warm water.).Take care not to stir the water as you add the food coloring.

Have students observe the long sides of the container to see where the blue and red food coloring travel. Example:  

• Ask students to draw a picture that describes their observations and then compare their pictures with pictures made by other groups.
• Did similar things happen to the food coloring in different groups? ( Answer: Results should be similar.)
• What happened to the blue, cold food coloring? ( Answer: It sunk. )
• What happened to the red, warm food coloring? ( Answer: The red, warm water rose towards the surface of the water and spread out above the blue, cold water.)
• What was the difference between the blue and red water? ( Answer: Temperature difference. If you have discussed density, students should know that there is also a density difference.)
• Do warm fluids (e.g. water or air) rise or sink compared to cold fluids? Explain why. (Answer: The temperature difference causes movement of water at different levels because less dense, warm water rises while the more dense cold water sinks.)
• (Advanced Question)  Using knowledge from Parts 1 and 2, how could you apply this idea of warm, water rising and cold, water sinking to the air in the atmosphere since both are fluids?
• Ask students to imagine a situation similar to Part 2, except this time, a cup of ice water is substituted for the cup of hot water.How would the circulation look? (Cold water should flow along the bottom of the saucer until it nears the warmer sides. Then it will rise up. As it reaches the top, the water will cool and sink, drawing water from the sides in toward the center.)

A fluid is any substance that flows. Fluids include liquids, gases, and some solids like glacial ice. Fluids take the shape of a container because they do not have a specific shape and include common substances like water, shampoo, sunscreen, honey, and air. Air is a mixture of gases that flows and takes the form of its container, so it is a fluid.

Fluids flow due to different densities. The chemical composition of fluids influences density. For example, fresh water is less dense than salt water; therefore, salt water is heavier and sinks below the freshwater. Another example (as seen in Part 1) is that carbon dioxide is heavier (denser) than air, allowing carbon dioxide to force air out of the way and extinguish the fire. The fire cannot continue without a supply of oxygen, such as the oxygen found in air.

Temperature changes can also affect the density of a fluid. Adding heat to a fluid increases the motion of the molecules, which then spread further apart. Warm fluids are less dense and rise while cold fluids are denser and sink. The circulation of rising and sinking air is called convection.

Convection is the transfer of heat by the movement of a heated material. In the atmosphere, on a hot summer day, the surface of the Earth is heated by energy from the Sun. Then, the warmed Earth surface warms air near the ground. The warm air rises, while cooler air sinks towards the ground. That cooler air is then warmed by the Earth's surface and rises, continuing the convection pattern. Convection plays a key role in the formation of clouds and even thunderstorms. There is a limit of how far the warm air can rise in the atmosphere because air temperatures decrease with increasing altitude .

The continual cycling due to temperature-driven density, convection currents, are found in many places and on many scales in the atmosphere, ocean, and even in the Earth's interior. Smaller convection currents can be found in a cup of hot cocoa or a fish tank. Convective motions in the atmosphere are responsible for the redistribution of heat from the warm equatorial regions to higher latitudes and from the surface upward.

The main three processes of heat transfer include radiation, conduction, and convection.

Consider what happens to the water in a pot as it is heated over an open camp stove.In this example, radiation transfers heat from the burner to the pot. ( Additional background information on radiation can be found here .) Convection moves heat and water in the pot. The water at the bottom of the pot heats up first and expands. Since the warmed water has a lower density than the water around it, it rises up through the cooler, dense water. At the top of the pot, the water cools, increasing its density, which causes it to sink back down to the bottom. This movement distributes heat within the pot.

Related Resources

• Radiation and Albedo Activity
• How Clouds Form
• Atmospheric Circulation
• Virtual Balloon Activity

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Convection Snakes

September 12, 2011 By Emma Vanstone 8 Comments

This is a lovely activity to demonstrate convection . Younger children will love it just for the moving snake, and it’s a great way for older children to start to understand what convection means.

This activity requires a source of heat, so adult supervision is essential.

You will need

Paper snake Cotton thread

Tape Scissors Colouring pencils A heat source

How to make a spinning snake

1. Draw a snake on a sheet of paper in a spiral shape or use the convection snake template .

2. Colour and decorate as you wish.

3. Cut out the snake so that it makes a spiral.

4. Tape the cotton to the centre end of the snake.

6. Hold the snake over a heat source such as a candle or radiator.

The snake spiral should start to spin.

Why does this work?

Convection is the transfer of heat in a fluid. A fluid is usually a liquid or a gas!

In the case of the snake, moving air particles make the snake spin. As the air near the heat source warms, the particles move further apart. This makes the air less dense, and so it rises and is replaced by cooler, more dense air. As the air particles rise, they cool again and become denser, which makes them sink, and the cycle continues. This circular movement of air particles rising and falling causes the snake to spin. This is a convection current .

This process is how radiators work to heat our homes. The hot water inside the radiator heats the radiator through the process of conduction. Then the hot radiator heats the air around it, which spreads into the room as it becomes less dense. This is replaced by cooler dense air, which is then heated!

Last Updated on April 29, 2024 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Reader Interactions

September 14, 2011 at 2:15 pm

Wow! What a fun experiment!!! Love it! I remember those funny curly whirly things you would place on your palm, but these snakes are much better and show the effect of heat more! Love it!

Thanks for sharing on Kids Get Crafty!

September 14, 2011 at 10:10 pm

Thanks Maggy. We love Kids Get Crafty! xx

September 15, 2011 at 7:39 pm

Great experiment! I remember making these at school!

Thanks for linking up to Handmade Thursday! My Son will LOVE your site 🙂

September 15, 2011 at 9:00 pm

I hope he does. Let us know if you try any experiments out. x

September 19, 2011 at 1:26 am

oh, I love finding fun science experiments so I am SUPER excited to have found you!!

would love to invite you to link this up to the Sunday Showcase – http://momto2poshlildivas.blogspot.com/search/label/Sunday%20Showcase

September 19, 2011 at 9:12 pm

great project! and thanks for giving me a refresher course on what exactly convection is! (a little sad given that I have a BS in physiology) Thanks so much for sharing on Craft Schooling Sunday, great to have you!

September 25, 2011 at 12:48 pm

That’s pretty cool. I’ve seen this snake for wind, but it’s fun to see it used for something else.

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Heat Transfer - Convection

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Convection Heat Science Experiment

Categories STEM Activities , Science Experiments

Use these simple heat experiments to show kids how convection heat works and why heat rises right in front of their eyes. Fascinating science experiments for kids! 

I’ve wanted to try convection heat experiments with my kids for quite some time now. It looked so magical and other-wordly to see all those pearly colors swirling around with the heat. We learned some valuable lessons about exactly where the heat from our stove is coming from, too, which is probably why it cooks food so unevenly!

If you conduct this experiment with a large group, I recommend using a hot plate. First, because it is easier to haul around, and secondly, it produces a more even, low heat, which is better for seeing swirls.

Our mixture eventually got to hot and it didn’t look as cool when the dye moved from place to place.

Learn what is convection heat for kids!

Learn About What is Convection for Kids!

Try this easy convection heat experiment in the classroom or at home!

Related: STEM Activities for Kids!

The Science: How Convection Heat Works

When you heat a fluid, its density is reduced and volume is expanded. At first, the soap and the water is evenly disributed in the pan, but when it heats up, the liquids at the bottom get warm first. This causes them to become less dense and rise to the top. The cool liquid is pushed to the bottom of the pan, where it in turn is heated and pushed to the top.

The pearly soap and food coloring make this easy to see.

What You’ll Need for the Convection Heat Experiment:

Disclaimer: This post includes affiliate links for your convenience at no cost to you.

• Aluminum pie plate (or a regular pie or cake pan)
• Liquid food coloring
• A pearly shampoo or conditioner ( we used my husband’s Old Spice , it was the only pearly soap we had!)
• Stove or hot plate

First, mix your soap and water in a 2 to 1 ratio with twice as much water as soap. You will want to just cover the bottom of the pan (at least, ours worked better with a shallow amount of water). Try not to make extra bubbles.

You can leave the mixture its original color, or add dye to the entire pan. Bo was excited to add the food coloring, which is why we dyed our base soap.

Turn the heat on low and wait. You will see the liquid starting to rise by the changes in the color of the soapy water.

Once it starts to turn over, it’s ready to add more dye.

Drop a drop or two of food coloring in different areas of the pan. Watch as it is slowly rolled into the other colors. 

Convection heat at work!

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Share this project with a friend!

These facts are examples of the transfer of heat by convection. Unlike conduction, in convection it is the material itself that moves, therefore you can't have convection in a solid. In liquids and gases convection takes place because the hotter, low-density fluid rises taking the heat energy with it - this is called a convection current. The bigger the surface area of an object the more air can move round it in convection currents and the faster it will cool. Think of the motorbike cooling fins. In the photograph the candle flames are bending inwards. This is because there is an updraft of air at the centre and this is drawing in cold air from the sides pushing the flames towards the centre. You can demonstrate convection by the following simple experiments.

1. Convection in water Fill a beaker with cold water and then carefully drop a few crystals of potassium permanganate into it so that they fall close to one side of the beaker. Now heat the base of the beaker just under where the crystals have fallen. You should see the colour rise up this side, go across the top and then fall down the other side of the beaker � this is a convection current. You can also use the special piece of apparatus shown in the diagram. It is a "square " glass tube filled with water. Drop a crystal of potassium permanganate into the top and then heat one of the bottom corners gently. You will see the colour begin to move round the tube going down the limb opposite the heating and then rising up the other side above the Bunsen due to convection currents in the water.

2. Convection in air (a) simply hold your hand above the bunsen flame. You can easily feel the hot air rising. (b) Use the apparatus shown in the diagram. Light the candle and then hold a piece of smouldering paper or string over the top of the other chimney. The smoke should be pulled down that chimney and rise up the other chimney with the hot air above the candle. 3. Make a small rotor out of aluminium foil and hold it above a bunsen burner to test the effect of the convection currents in the air. What is actually is convection? Convection occurs because the air (or other fluid) is heated, expands, becomes less dense and so rises through the more dense colder air

Land and sea breezes