Camp Yellow Scope: Drops & Detergents

Welcome back Campers!

It’s Week 2 of Camp Yellow Scope: Drops & Detergents! If you missed Week 1 of Camp Yellow Scope, don’t worry, we’ve got you covered. Click on Newton, our friendly lab rat (and fellow camper) to check out last week’s exciting experiments with milk and food coloring.

Click here to download printable instructions. You can also print out a lab worksheet to record your observations, jot down ideas, and design your own experiments! If you collect your worksheets together from all eight weeks, by the end of the summer you’ll have your very own Camp Yellow Scope notebook! You can even add some extra sheets for new experiments you design yourself.

Experiment 1: Drop & Flop

When you think of summer, what comes to mind? Beaches, water parks, and neighborhood pools? Water and summer go hand-in-hand. You’ve probably noticed that when water splashes on the edge of the pool or other surfaces, it forms droplets, instead of spreading out evenly into a thin layer. But have you ever wondered why water forms drops?

This week we’re going to explore the wonderful world of water and find answers to this question! How many drops of water do you think can fit on a penny? Five? Ten? Let’s experiment to find out!

Let’s get started!

Clear a space on the kitchen counter or another flat surface and get ready to science!

Hypothesis

How many drops of water do you think you can stack on top of a penny before they spill off? Will the drops sit beside each other or pile up? Record your hypotheses on your lab worksheet.

Instructions

1. Put on your safety goggles, if you have some. If you wear glasses, that works, too!
2. Add half a cup of water to each of the two cups. Label cup 1 as “Plain Water” and cup 2 as “Soapy Water”.
3. Add one teaspoon of dish soap to cup 2. Stir gently to mix.
4. Place one of the pennies on a flat surface.
5. Fill the dropper with plain water from cup 1.
6. Carefully add drops of water to the penny, one by one, counting as you go.
7. Keep track of the number of drops you add until the water spills over the edge of the penny.
8. Record the number on the table below.
9. Place the second penny on the flat surface and repeat the experiment, this time adding drops of the soapy water from cup 2, counting as you go.
10. Record the number of drops of soapy water you were able to add until the water spilled off the penny.
11. Now repeat the experiment two more times for each condition – Plain Water and Soapy Water – and record the number of drops on the table.
12. Calculate the average for each condition. (See the sticky note for help with how to calculate an average.

Observations

What did you observe? What shape did the plain water drops form? How about the soapy water? Did the penny hold more drops of the plain water or the soapy water? Record your observations on your lab worksheet.

What’s happening?

You probably noticed that the plain water formed round drops that merged together to make a tight dome of water on top of the penny. This is due to surface tension. Surface tension happens because water molecules are attracted to each other - they want to stick together. The molecules at the surface of the water get tugged on unevenly by the water below. This pulls the surface molecules inward, forming a strong and flexible film on the water’s surface. As you add more drops, the force of gravity becomes stronger than the surface tension forces. When this happens, the water spills over the edge of the penny.

So why didn’t the soapy water form a tight dome? As you learned last week, soap molecules are made up of two different ends – a water-loving end and a water-hating end. As the water-hating ends try to move away from the water molecules, they push to the surface. This weakens the attraction between the water molecules and breaks the surface tension, so the water can’t form drops.

Why does it matter?

Can you think of ways surface tension is important in your everyday life?

• Insects such as water striders are able to walk across the surface of the pond because of the tight film (surface tension) on top of the water.
• Have you noticed the red liquid in a thermometer? It’s able to rise and fall because of surface tension.
• Your raincoat has likely been treated with water repellent materials that cause water to “bead up” instead of soaking into the fabric.

You own it! Test yourself: True or False?

1. Soap can reduce surface tension.
2. More drops of soapy water can fit on a penny than plain water.
3. Surface tension allows insects to walk on water.

Answer Key:
1. True.
2. False. More drops of plain water can fit on a penny because of surface tension.
3. True.

We hope you had fun learning about water droplets, soap, and surface tension! Next week at Camp Yellow Scope, we’ll do one more set of experiments using dish soap. This time we’ll use soap to isolate DNA from fruit. How cool is that?!

We'd love to see how your experiments turned out! How many drops of water could you fit on a penny? Share your photos or videos:

• Facebook: Yellow Scope Science Kits for Girls
• Twitter: @YellowScopeGirl, #CampYellowScope
• email: info@yellow-scope.com

For more exciting experiments, check out our science kits on the SHOP tab of our website!