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Drops Of Water On A Penny

Have you ever thought about how many drops of water can fit on a penny ? Try this fun science experiment with things found in your purse or pocket! Explore the surface tension of water with this fun and easy penny lab with the kids. We are always on the hunt for simple science experiments , and this one is just super fun and easy!

Explore How Many Water Drops On Penny

Add this simple penny lab to your science activities this season. If you want to learn about the surface tension of water, let’s dig in. While you’re at it, make sure to check out these other fun water science experiments.

Exploring water drops on a penny is a fantastic science experiment for kids because it’s simple and fascinating. By placing drops of water onto a penny, kids can observe how the water beads up and forms a dome-like shape, defying gravity.

This phenomenon occurs due to surface tension , the cohesive force that causes water molecules to stick together. Through this experiment, kids can learn about surface tension and how it affects the behavior of liquids. They can also experiment with variables such as the number of water drops or the penny’s cleanliness to see how it impacts the results. Additionally, this experiment can be efficiently conducted with everyday household items, making it accessible and engaging for scientists of all ages.

Water Drops On A Penny Project

You can also easily turn your penny experiment into a fantastic presentation along with your hypothesis. Check out the resources below to get started.

• Easy Science Fair Projects
• Science Project Tips From A Teacher
• Science Fair Board Ideas

Penny Lab Experiment In The Classroom

TIP: If you want to add a little variety to this experiment, swap out the pennies for nickels, dimes, and quarters. Ask your students to guess how many drops will fit on each coin. Record the date from the experiment and make a class graph chart with your results!

Additional ideas for penny lab hypotheses include using different liquids or clean vs. dirty pennies . What else can you think of when creating an experiment?

Get Your Free Printable Penny Lab Guide!

Penny Lab Experiment

Let’s investigate how many drops of water can fit on a penny. Grab your purse, turn over the couch cushions, or break out the piggy bank; it’s time to find some pennies to experiment with!

• Eyedropper or pipette
• Food coloring (makes seeing this in action MUCH easier, but is optional)
• Small bowls

Penny Experiment Set Up:

STEP 1: Add water to both of your bowls, and one of them, add green food coloring. This is optional if you want to see the drops a bit better.

STEP 2: Use an eyedropper or pipette to pick up and carefully drip one drop of water at a time onto the penny.

STEP 3: Count how many drops you can fit onto one penny until the water overflows.

We were able to get ours up to about 27! Go ahead and record the data for separate trials on the same coin. What can you conclude?

Why Do So Many Drops Of Water Fit On A Penny?

Were you surprised that a lot more drops of water fit on a penny than you predicted? We had 27 drops of water on ours!

What property of water allows the water to stick to the penny? Surface tension and cohesion are why you can get so many drops of water on a penny.

Cohesion is the “stickiness” of like molecules to one another. Water molecules love to stick together! Surface tension is the result of all the water molecules sticking together. Learn more about the surface tension of water !

Once the water has reached the edge of the penny, a dome shape begins to form. This is due to the surface tension forming a shape with the least amount of surface area possible (like bubbles )!

What happens if you use a different liquid like alcohol? Can you as many drops on a penny?

More Fun Penny Experiments

• Sink the boat challenge!
• Penny Spinners
• Green Pennies Experiment
• Paper Bridge STEM Challenge
• Lemon Battery STEM Project

Use the Scientific Method

This drops of water on a penny experiment is a fantastic opportunity to use the scientific method and record your experiment using the free mini worksheet pack below.

You can read about using the scientific method here , and find more information on the independent and dependent variables !

The first step in the scientific method is asking a question and developing a hypothesis.

Apply the scientific method to this drops-on-a-penny science activity and turn it into a surface tension experiment by choosing a question to investigate.

• How many drops do you think will fit on a penny? (PREDICTION)
• What happens when one drop of water meets another drop? (OBSERVATION)
• Which coin held the most water? (EXPLANATION)
• Can you think of everyday examples of surface tension? (APPLICATION)

Helpful Science Resources To Get You Started

Here are a few resources that will help you introduce science more effectively to your kiddos or students and feel confident yourself when presenting materials. You’ll find helpful free printables throughout.

• Best Science Practices (as it relates to the scientific method)
• Science Vocabulary
• 8 Science Books for Kids
• All About Scientists
• Science Supplies List
• Science Tools for Kids

More Science Experiments To Try

Check out our list of science experiments for Jr Scientists!

• Walking Water
• Rubber Egg Experiment
• Why Do Things Float In Salt Water?
• Water Density Experiment

Printable Science Projects For Kids

If you’re looking to grab all of our printable science projects in one convenient place plus exclusive worksheets and bonuses like a STEAM Project pack, our Science Project Pack is what you need! Over 300+ Pages!

• 90+ classic science activities  with journal pages, supply lists, set up and process, and science information.  NEW! Activity-specific observation pages!
• Best science practices posters  and our original science method process folders for extra alternatives!
• Be a Collector activities pack  introduces kids to the world of making collections through the eyes of a scientist. What will they collect first?
• Know the Words Science vocabulary pack  includes flashcards, crosswords, and word searches that illuminate keywords in the experiments!
• My science journal writing prompts  explore what it means to be a scientist!!
• Bonus STEAM Project Pack:  Art meets science with doable projects!
• Bonus Quick Grab Packs for Biology, Earth Science, Chemistry, and Physics

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Drops on a Penny

Hydrogen bonds and surface tension give water some amazing properties. let's use them to see how many drops of water fit on a penny.

Print this Experiment

You might think that you can’t fit many drops of water on the surface of a penny. Pennies are just so small! In the Drops on a Penny experiment, though, you’ll experience surface tension and cohesion at their finest. How many drops of water can you fit? There’s only one way to find out… by adding one drop at a time!

Experiment Videos

Here's What You'll Need

Eyedropper or pipette, let's try it.

Wash and rinse a penny in tap water. Dry it completely with a paper towel.

Place the penny on a flat surface. The flatter the surface, the better this experiment is going to go.

Use an eyedropper or pipette to draw up water.

Carefully, drop individual drops of water onto the flat surface of the penny.

Keep track of the water drops as you add them, one at a time, until water runs over the edge of the penny. You’ll probably be surprised by the number of drops you get on there!

How Does It Work

There are two properties at work in this experiment: cohesion and surface tension. Cohesion is the attraction of like molecules to one another. In this case, the like molecules are the H20 molecules in the water drops. Surface tension is a special term we use to describe the cohesion between water molecules.

Water’s cohesion and surface tension are special because of hydrogen bonds. Hydrogen bonds are formed by the hydrogen atoms of one molecule being attracted to the oxygen atoms of another molecule.

The cohesion and surface tension of water becomes apparent when the drops of water you add to the penny reach the penny’s edge. Once the water has reached the edge, you begin to see a bubble or dome of water forming on top of the penny. The bubble shape is a result of the water molecules clinging to one another in an optimal shape (just like the bonds on the surface of a blown bubble).

Take It Further

Extend this experiment by trying different coins such as dimes, nickels, or quarters.

Science Fair Connection

Demonstrating the cohesive properties of water is pretty cool, but it isn’t a science fair project.  You can create a science fair project by identifying a variable, or something that changes, in this experiment.  Let’s take a look at some of the variable options that might work:

• Try testing different liquids such as vegetable oil, salt water, soda, etc. How does this change the number of drops the penny can hold?
• Try testing surfaces with different shapes. Do circular surfaces hold the same amount of water as rectangular surfaces with approximately the same surface area?

That’s just a couple of ideas, but you aren’t limited to those! Try coming up with different ideas of variables and give them a try.  Remember, you can only change one thing at a time.  If you are testing different liquids, make sure that the other factors are remaining the same.

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Drops of Water on a Penny {Awesome Science!}

April 13, 2021, join the conversation, categories/tags:, ages 5-7 ages 8-10 stem activities, want these great ideas sent right to your inbox sign up for the newsletter..

How many drops of water fit on a penny? Here’s a quick and easy science experiment that kids will love because the results are impressive!

This science experiment teaches kids about the concept of surface tension. They’ll also be exploring how soap destroys surface tension by pushing the water molecules apart from each other.

When you ask kids how many drops of water will fit on a penny, they’ll probably guess 3 or 4 drops. Maybe 5. Everyone knows that drops of water aren’t very big, but then again, neither is a penny! So a penny probably won’t hold many drops.

Kids will be very surprised to find out how many drops of water a penny can hold. It’s actually a LOT!

This post contains Amazon affiliate links, which means that I earn from qualifying purchases at no additional cost to you .

In this experiment, we’ll compare the surface tension of water with the surface tension of soapy water. Soap greatly decreases surface tension!

The procedure for this experiment is simple. Use a dropper/pipette to drop water onto a penny. Carefully count the drops as you go. These plastic pipettes work well. We like having them on hand for all kinds of activities.

It’s just amazing to watch the drops of water pile up on the penny! We tried this several times, and we were able to get 23-27 drops on the penny each time before the water ran off the side.

Then we compared the surface tension of plain water with soapy water. Would we be able to get the same number of drops of soapy water onto the penny?

Nope. Only 12-15. We could only get about half as many drops of soapy water on the penny before the water ran off over the side.

The Science Behind the Penny Drops Experiment

The way water creates a rounded surface is called surface tension. Surface tension is what allows you to fill a glass all the way to the top… and then some! It’s what gives the water the domed look on the penny.

Water has strong surface tension because of its polarity. Water molecules are polar, meaning that one end of each molecule has a positive charge while the other end has a negative charge. Because of these opposite charges, water molecules are attracted to each other. They form hydrogen bonds with each other. If you’re working with young kids, you can tell them that it’s like the water molecules are holding hands with each other and they don’t want to let go! This is what is happening on top of the penny.

Soap decreases the surface tension of water by pushing apart the water molecules. Each soap molecule has an end that is attracted to water and an end that repels water. The hydrophobic ends of the soap molecules (the ends that don’t want to be near water) squeeze their way between water the molecules as they work their way to the surface. You can read more about soap and its effect on surface tension here .

Need more simple science ideas? We have tons of educational and engaging science experiments!

See more than 25 Cool Science Experiments here .

Gloria Aug 28, 2023

I love all these experiments and even better the simple way to explain them . Thank you

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Drops of Water on a Penny Science Experiment

Discover how many drops of water fits on a penny in this simple and easy science experiment. Your kids will be shocked at how many drops of water can a penny hold due to surface tension!

How many drops of water can fit on a penny?

If you ask your child how many drops of water they think will fit on a penny, they will probably respond with a low number. After all, a penny isn’t that big, so it’s not obvious that a coin can hold that much water.

This drops of water on a penny science experiment will amaze your kids and teach them about surface tension. There are also a lot of science extensions you can do to make the experiment even more interesting. Don’t be surprised if your kids want to squeeze drops of water on all the coins in your house after this experiment!

This simple experiment is easy enough for preschoolers to do, though you will need to monitor closely to make sure they are not squeezing too much water out of the dropper at once. Kindergartners and first graders should be able to do this experiment with minimal help.

If you are doing this experiment in a classroom setting, you can also tally up the number of drops on the penny for all the students and calculate the average. It would be interesting to see if everyone got around the same count!

Drops of Water on a Penny Science Experiment 

• Free drops of water on a penny experiment worksheet
• Dropper or pipette
• Small container
• Optional: paper towel

Instruction for Penny Drop Experiment :

1. Place your penny on a flat surface. If you are worried about getting water on the table or the floor, you can place a paper towel underneath the penny.

2. Pour some water in a small container.

3. Ask your child to predict how many drops he or she thinks will fit on the penny. Record the hypothesis on the worksheet.

4. Use a dropper or pipette, suck up some water and carefully start dropping the water on the penny. Make sure to count as you go!

5. When the water spill over, stop counting.

6. Record how many drops of water ended up fitting on the penny on the worksheet. Was the hypothesis close?

I explained to my son that water likes to stick together. Just as I was about to describe surface tension, he lost focus and squeeze a drop of water right next to the penny but on the floor. As a result, the water on the penny spilled onto the floor.

Instead of being disappointed, he took the opportunity to explain to me that the water that he dropped on the floor pulled the water on the penny off since water like to stick together. I was so proud that he made this observation!

Science Behind drops on a Penny Lab Experiment 

Water molecules like to be around other water molecules, just like you like to play with your friends. When water drops fall, they like to get as close to each other as they can. It is kind of like they are giving each other a hug and holding hands.  That is why you have a puddle on the ground when it rains, instead of a whole bunch of raindrops! 

This special hug has a special name, cohesion. Cohesion means that water likes to be close to water. When the water gets close it forms a rounded shape like a bubble. This round shape stays tall and solid because of something called surface tension . Surface tension is the way the molecules hold on to each other to stay close.

To make this drops of water on a penny science experiment even more interesting, you can try using different types of liquids to see if you end up with the same count. Try vinegar, fruit juice, honey, and oil. Make sure to ask your kids questions about their hypothesis and why before conducting the experiment.

You can also try this experiment with different coins! Does the dime hold less water than the nickel because the dime has a smaller surface area? How about in comparison to the penny?

How Many Drops of Water can Fit on a Penny?

The answer to how many drops of water can fit on a penny will vary depending on the dropper you use and the pressure with which you squeeze out the water. If you squeeze harder, your water droplets may be larger, and therefore you will end up with a smaller number of drops.

When my son and my daughter tried this experiment, we all got different results. The numbers weren’t too far off, but they were all different nonetheless.

I counted 35 drops of water before the water spilled over. How many did you get?

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Drops on a Coin

Activity length, 10-15 mins., activity type, discrepant event (investigatable).

In this demonstration, students' assumptions are challenged as they observe the power of surface tension in water droplets.

Although a water molecule has an overall neutral charge, the actual structure of a water molecule makes it a polar molecule (it has a positive end and a negative end). The two hydrogen atoms are slightly positive, and the oxygen atom is slightly negative. A weak link occurs between the negatively charged oxygen atom of one water molecule and the positively charged hydrogen atoms of a neighbouring water molecule. This weak link is called a hydrogen bond . The polarity of the water molecule can also cause it to be attracted to molecules of other polar substances.

There are two types of "stickiness" in this demonstration: cohesion and adhesion.

The attraction between water molecules is called cohesion . The cohesive force that occurs between water molecules is so strong that, at the water's surface, it creates a "skin", which is known as surface tension . Surface tension is strong enough to support insects that crawl across the water's surface, like water striders (Gerridae).

The attraction of water molecules to other substances, like soil or glass, is called adhesion . As drops of water are added onto a penny, the adhesive force between the water and the penny keeps the water from falling off.

Cohesive forces are strong, but not unbreakable. As a water drop builds up and out, usually bulging over the sides of the penny, the cohesive forces will eventually be overcome by the force of gravity on the water molecules. The "skin" will burst, and all of the water will spill off.

The cohesive forces between polar molecules are stronger than those between non-polar molecules, such as those in oil or syrup. That's why you can make a bigger "pile" of water than of oil or syrup.

Describe the cohesive and adhesive properties of water.

Per Student or Pair: 5 cent coin or penny an eyedropper water mineral/baby/olive oil corn syrup

Key Questions

• How many drops of water they think a coin can hold? Were your predictions correct?
• Does it matter if the coin is heads or tails?
• Will syrup/oil hold more or less drops than water? Why?
• How is it possible to get so many water drops on a coin?
• What causes the ‘skin’ on the surface of the big droplet?
• Would a 10 cent coin hold more or less drops? Why?
• Teacher Tip: Younger students may believe a 10 cent coin holds more because it is worth more despite being smaller.
• Place a coin on a table or desk.
• Holding the eyedropper close to the surface of the coin, carefully squeeze water droplets onto the coin, one at a time. The droplets should pool up on the coin, creating a big droplet of water. Get the students to count the drops.
• Stop squeezing when the droplet on the coin breaks up and overflows. The count is the number of drops that the coin could hold before the one that caused the coin to overflow.
• Wipe off the coin or use a new one.
• As before, gradually add drops of oil or syrup to the surface of the coin using the eyedropper. Get the students to count the drops.

Teacher Tip:  To make sure your count is accurate, hold the eyedropper far enough above the coin so that the drop has to fall a short distance before fusing with the droplet on the coin.

• Perform this as a student activity, rather than just a demo.
• Add a drop of soap/detergent to the water you use. It reduces the surface tension causing a dramatic reduction in the number of drops that will fit on the coin.
• Start with a full glass of plain water (with a dry rim to prevent the water from dripping down the side of the glass). How many coins can we add to the water without the glass overflowing?
• Gently add coins one by one. Because of surface tension, the water will rise above the rim of the glass before it spills (just like the initial experiment). Compare your original prediction with the number of coins you were able to add.

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Measure Surface Tension with a Penny

A soapy science activity from Science Buddies

By Science Buddies

Learn about the secrets of soap in this surprising surface tension-testing activity!

George Retseck

Key concepts Chemistry Molecules Surface tension

Introduction Have you ever noticed on a rainy day how water forms droplets on a window? Why does it do that instead of spreading out evenly over the whole surface? You might not guess it but this property of water is also related to washing dishes and doing the laundry. How? It all has to do with something called surface tension. Try this activity to learn more!

Background You have probably noticed that if you look at a surface outside on a rainy day or spill some water inside, the liquid tends to form droplets that stick up from a surface instead of spreading out into an even sheet. This occurs because water is made up of many tiny molecules that are all attracted to one another. Molecules in the middle of a drop of water are pulled evenly in all directions by all the nearby molecules. Those near the droplet’s surface, however, are pulled mostly inward by the water molecules below them. This creates "surface tension." The surface of the water droplet is held together by the attraction between molecules.

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Now, think about washing dirty dishes or clothing. There will be lots of tiny little holes and cracks that water needs to get into to wash away dirt and grime, such as the spaces between the fibers of a shirt or between a plate and bits of dried food. In order for water to flow more easily into these small spaces, you need to decrease its surface tension. You can do this by adding soap, which is a surfactant (a material that decreases the surface tension of a liquid). In this activity you will see how soap decreases the surface tension of water by putting water droplets on top of a penny.

Medicine dropper or eyedropper

Glass, cup or small bowl

Dish towel or paper towel

Flat, level surface that can get wet, such as a kitchen counter

Paper and pencil or pen (optional)

Preparation

Place your penny on a flat, level surface that can get a little wet, such as a kitchen counter.

Fill a glass, cup or small bowl with tap water.

Fill the medicine dropper with water.

Now carefully add one drop of water at a time to the top of the penny. Hold the medicine dropper just above the top of the penny (not touching it) so each new drop has to fall a short distance before it merges with the drop on the penny. You can write down the number of drops you add if you like. How many drops of water do you think will fit on top of the penny? Watch the drop on top of the penny carefully as it grows. It should keep getting bigger and bigger until it touches the edges of the penny.

Keep adding drops (refill your medicine dropper as necessary) one at a time. How big does the drop on the penny get before it finally spills over the edges?

Once the drop spills over the penny’s edge, use a towel to completely dry off the penny and surrounding surface. How many drops of water were you able to add before the water ran over the penny’s sides?

Mix a small amount of dish soap with your tap water.

Now, repeat the experiment using soapy water. Do you think you will be able to add more drops or less before the liquid spills over the sides of the penny? Again, slowly add one drop at a time. How big does the drop of water on top of the penny get before it breaks and flows over the edges?

Extra : Try the experiment with different liquids or other things you can find in your kitchen. (Make sure you have an adult's approval to use any liquids before you handle them.) How do different soaps and detergents like hand soap or laundry detergent compare with one another? What about other liquids like milk or juice? Which ones make the biggest (or smallest) drops? With the most or least number of drops?

Extra : Try using something other than a penny to collect the droplets. What happens if you use different materials, such as the flat top of a small plastic bottle cap or a button?

[break] Observations and results You should find that plain tap water produces a much larger, stable drop of water on top of the penny than the soapy water does. This is because plain tap water has higher surface tension, so the surface is "stronger" and can hold together a larger drop. Adding soap lowers the water’s surface tension so the drop becomes weaker and breaks apart sooner. Making water molecules stick together less is what helps soaps clean dishes and clothes more easily.

More to explore Sticky Water , from Exploratorium Soap , from Exploratorium Measuring Surface Tension of Water with a Penny , from Science Buddies Surface Tension Science: Build a Raft Powered by Soap , from Scientific American Science Activities for All Ages! , from Science Buddies

This activity brought to you in partnership with Science Buddies

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Penny Experiment with Water Drops

A penny experiment that demonstrates how water tension works and water can hold together in a dome shape – a super simple science experiment for kids!

Drop water on a penny and it just runs over the side, right?

Maybe not…

Maia was excited to show us a penny experiment she learned at school that demonstrated how water can hold together in a dome shape. This super simple science experiment requires only a penny, some water, and a dropper.

The Penny Experiment in Action

She showed us how we could carefully squeeze a drop of water at a time onto the top of the penny…

…and the droplets would combine to form a bubble of water.

Maia thought it looked a little like a snow globe (one of her favorite things).

We each tried the penny experiment to see how many drops of water it would take before it reached its limit. Because once it did, the water bubble burst and flowed over the edge of the penny.

Pretty cool, eh? We all had fun with this one. I think it’s definitely worth keeping it in mind for a rainy afternoon. Or just when you need a quick and easy activity for the kiddos.

By the way, if you want the technical explanation for why this works and what’s going on with the water, check out Steve Spangler Science .

3 More Favorite Simple Science Experiments for Kids

• The Rainbow Milk Science Experiment
• Make Painted Daisies
• Make a Baking Soda Volcano

P.S. Want even more science? Here’s my collection of The Best Kids Science Experiments to Try at Home .

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Penny Droplets

What you need.

• an eye-dropper
• liquid dish-soap
• a glass of water

What You Do

• Guess how many water drops you can fit on the front of a penny.
• Try it. How many drops will stay on the face of a penny without spilling water off the sides?
• Repeat the experiment, say, three times. The number of drops will probably come out about the same each time.
• Each time you do it, write down the number of drops.
• Add a tablespoon of dish soap to your glass of water. Stir gently, don’t make too many bubbles.
• How many soapy drops can you fit on the front of a penny now?
• Try it again.

What's Happening?

You just saw three important forces tugging on the water: gravity, cohesion, and adhesion. Gravity flattens the droplets, cohesion holds the droplets together, and adhesion holds the drops on the surface of the coin.

The cohesive force is the pull of the water molecules on themselves. Each successive drop sticks to the water that’s already on the coin. We often call this cohesive force “surface tension”. It’s what makes water drops look like they’re wrapped in invisible skins. Soap reduces the cohesive force, and breaks the surface tension. Soapy water makes smaller drops than plain water. Since soapy drops are smaller, more soapy drops will fit on a penny than plain water drops. Count ‘em!

Drops on a Penny Lab

Wendy has taught high school Biology and has a master's degree in education.

Table of Contents

Introduction, troubleshooting, discussion questions, how it works.

Have you ever noticed droplets of water sitting on a leaf after a rain shower? Instead of spreading out evenly over the leaf, the rainwater seems to form into separate balls. Why is this? Water has a special property called surface tension that makes its molecules cohesive, or ''sticky.'' This property also allows insects such as water striders to glide over the surface of a lake or pond.

In this activity, you will watch surface tension in action as you place drops of water onto a penny. How many drops do you think will stick together on the penny before spilling over the edge? Make a prediction before getting started.

To unlock this lesson you must be a Study.com Member. Create your account

For this physics lab you will need:

• An eyedropper

• A container of water

• Paper towels for clean up

• A notebook for recording data

1. Set the penny on a level surface.

2. Draw water into the eyedropper by squeezing the bulb at the top, then placing the tip into your container of water and releasing it.

3. Carefully place one drop at a time of water onto the surface of the penny, counting each drop as you go. Observe the collection of water on the penny getting larger and larger. What do you notice about its shape as it grows?

4. Continue placing drops on the penny, refilling your eyedropper if necessary, until the water finally spills off the edge. Record your final number.

5. Use a paper towel to clean up the spilled water.

6. Repeat the experiment three times to be sure data is consistent.

Be careful not to touch the tip of the eyedropper to the water as you drop it onto the penny. This might make it spill sooner!

• Was your prediction close to the actual number of water drops that fit onto the penny? Were you surprised at the final number?
• How do you think this experiment would vary if you tried different liquids?

In order to understand surface tension, we need to zoom in and take a closer look at a water molecule. You may already know that the chemical formula for water is H 2 O. This means that water is made up of two hydrogen atoms bonded to one oxygen atom.

Surprisingly, these atoms have very slight electrical charges. (Seems strange, since water and electricity usually don't mix!) The oxygen atoms are slightly negative in charge, and the hydrogen atoms are slightly positive in charge. Now, you probably know that opposite charges attract. So when water molecules are surrounded by each other, their charges will pull them together and make them stick; this is what we call surface tension .

It is for the same reason that the drops of water stay together on the penny. Their attraction for each other holds them together in a tidy mound, until the volume just becomes too great and they spill over.

Let's take a last look at our example of the water strider on the lake. Do you see the effects of surface tension as the water strider moves easily on the surface of the water? This layer of water is held together by invisible bonds, creating a surface on which the insect glides as if on ice.

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• TeachEngineering
• Wet Pennies

Hands-on Activity Wet Pennies

Grade Level: 7 (6-9)

Time Required: 15 minutes

Expendable Cost/Group: US $1.00

Group Size: 4

Activity Dependency: How Many Drops

Subject Areas: Physical Science

NGSS Performance Expectations:

Curriculum in this Unit Units serve as guides to a particular content or subject area. Nested under units are lessons (in purple) and hands-on activities (in blue). Note that not all lessons and activities will exist under a unit, and instead may exist as "standalone" curriculum.

• Does Your Chewing Gum Lose Its Sweetness?

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Engineering connection, learning objectives, materials list, worksheets and attachments, more curriculum like this, pre-req knowledge, introduction/motivation, vocabulary/definitions, investigating questions, troubleshooting tips, activity extensions, user comments & tips.

Chemical engineers apply their understanding of natural scientific properties, such as surface tension, as they design experiments to create new materials and products that behave as they desire.

After this activity, students should be able to:

• Give an example of a hypothesis that is based on an observation of a natural phenomenon.
• Give an example of an experiment designed to address a specific hypothesis.

Educational Standards Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards. All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN) , a project of D2L (www.achievementstandards.org). In the ASN, standards are hierarchically structured: first by source; e.g. , by state; within source by type; e.g. , science or mathematics; within type by subtype, then by grade, etc .

Ngss: next generation science standards - science.

Common Core State Standards - Math

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State standards, north carolina - math, north carolina - science.

• 3 small beakers (50-100 ml) or plastic cups (about 4 to 8 ounces) per group
• 1 disposable pipette per student, plus a few extras
• 1 penny per student
• rubbing (isopropyl) alcohol, two 16-ounce bottles
• vegetable oil, one 32-ounce bottle
• paper towels, several per student

Students should be able to calculate the average of four numbers less than 50.

This activity engages students' attention very quickly and thus requires little or no introduction. Simply divide the class into teams of four students each, provide the materials and written instructions for students, and let them proceed with the activity.

Before the Activity

• Gather materials and make copies of the Wet Pennies Handout .
• As indicated in the student instructions, each team needs three containers (beakers or cups) of liquid: one containing water, one containing rubbing alcohol, and one containing vegetable oil. For each liquid, use about 2 ounces (about one-half inch of liquid height). Label the containers.

With the Students

• Divide the class into groups of four students each.
• Pass out the materials and handouts. Emphasize the need to follow the instructions carefully, especially in regard to the order of the liquids they test on their pennies.
• After the experiment is done, lead a concluding class discussion, as described in the handout and Assessment section. Ask the Investigating Questions.

hypothesis: A tentative explanation for a fact or set of observations, which can be tested objectively.

Concluding Discussion : As outlined in the Wet Pennies Handout , lead a class discussion so students can share and compare results and conclusions. Ask the Investigating Questions. Listen to students' discussion contributions and answers to gauge their level of comprehension.

• How many drops of water fit on your penny? Was this number similar to the number other members of your group got? What do you think could cause differences between the numbers you got? (Students might respond that individuals have different dropping styles [speed, height they hold the pipette above the coin, etc.] and that newer pennies seem to have a more distinct rim, which could allow more water to stay on the penny. They might also speculate that differences between the pipettes could cause different sized drops to form.)
• Did you get different averages for the three liquids? If so, which liquid allowed you to put more drops on the penny?
• Are your results consistent with those of other groups? In what ways are they the same or different?

Some students may get the mistaken idea that the water-dropping activity is some sort of contest that they can win by getting the most drops, of any liquid, on the penny. Try to avoid giving students this idea, and if they come up with it on their own, explain that the point is for them to be able to fairly and accurately compare the numbers of drops of each liquid a penny can hold -- not to compare how many drops each student can get a penny to hold. To fairly and accurately compare the number of drops of each liquid a penny can hold, students need only try to use the same dropping technique (same squeezing pressure on the pipette bulb, same height it is held above the penny) for each liquid.

Students may want to immediately test the hypotheses they develop as part of this activity. If time allows, some of the ideas they are likely to generate can be quickly and easily tested, and it is a good idea to encourage their enthusiasm by letting them do so. See the Lesson Closure and Lesson Extension Activities sections of the How Many Drops? associated lesson or more information.

In this lesson and its associated activity, students conduct a simple test to determine how many drops of each of three liquids can be placed on a penny before spilling over. The three liquids are water, rubbing alcohol, and vegetable oil; because of their different surface tensions, more water can ...

Through two lessons and their associated activities, students do the work of scientists by designing their own experiments to answer questions they generate. Through a simple activity involving surface tension, students learn what a hypothesis is—and isn't—and why generating a hypothesis is an impor...

Students explore an important role of environmental engineers—cleaning the environment. They learn details about the Exxon Valdez oil spill, which was one of the most publicized and studied human-caused environmental tragedies in history.

Contributors

Supporting program, acknowledgements.

This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

This activity was originally published, in slightly modified form, by Duke University's Center for Inquiry Based Learning (CIBL). Please visit http://ciblearning.org/ for information about CIBL and other resources for K-12 science and math teachers.

Last modified: January 10, 2019

Drops on Coins

How many drops of water can be held on a coin? Find out today with this quick & easy experiment!

Coin (penny), water, dropper.

Time Estimated:

Directions: .

Wash and dry coin.

How many drops of water do you think can fit on the coin? Make a hypothesis (educated guess) and then find out!

Drip one drop of water at a time onto the penny using a dropper, pipette, or drip from a spoon in a crunch! Count each drop!

Think Like A Scientist!

Did the coin hold more or less drops than you predicted? Why do you think that was?

Try the same experiment again and count your drops! Was it the same number? Was it close? This difference is called experimental error. If you have a big difference between your two tests (trials), then you have a large experimental error. This means that maybe your dropper isn’t very precise. What could you do to reduce this error? Let other scientists know in the comments below!

What other coins could you use? Would they be able to hold more or less drops? Let us know what you find out in the comments below!

How It Works:

In this experiment, did your penny hold more drops than you thought it would?? This happens to a lot of scientists!

One reason that this happens is because of a property of water called cohesion. Cohesion is when two molecules that are similar to each other stick together. Water molecules are the same, and so they stick together and help keep drops on top of the penny.

Another property of water that helps the penny hold a lot of drops is called surface tension. Surface tension is a special term used to describe cohesion for water!

Did you notice a bubble shape start to form on the top of the coin? Without cohesion and surface tension it would just drip down the sides of the coin and you wouldn’t be able to hold nearly as many drops of water! These two forces help pull all of the water molecules in from the sides so that they stay in a bubble on top of the coin for longer than you might expect!

Looking for more fun at home STEM activities for your young scientist? Check out our workbook full of exciting science experiments and empowering activities! 

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