Investigation Sequence
Title
Surface Tension 2Marcia Kautsch and Melissa Schroeder
Date
Focus Questions
What is surface tension? What affects surface tension? What do scientists do to try to answer questions? What would a scientist do if they made a mistake?
Concepts
Content: Earth, Physical, & Life
Surface tension is molecules pulling and stretching to form a skin to the
water.
Surface tension is weakened by different materials.
Cross cutting concepts
Science Practice
Personal, Social, Technology, Nature of Science, History
Scientists create questions, design an experiment, and use observations to
answer their questions.
All scientific ideas are tentative and subject to change and improvement.
Background information
In all water the molecules are attracted to each other in all different directions this causes surface tension. The air on the surface creates a tighter more uniformed surface tension because the water molecules are only being pulled in and down.
Activity Sequence
1. Putting your two cents in.2. Surfing surface tension.
3. Will it drip?
4. How to give pepper some pep?
5. Attract or repel?
6. Boat racing.
Activity Descriptions
Activity One
Putting your two cents in.
Materials: clear cup, food coloring, white paper, and 60 pennies
1. Ask students how many pennies will fit into the cup before water drops on
paper?
2. Ask what scientists would do to answer the question.
3. So if we try this, write in your science lab book how many pennies you think
can be put in before it over flows.
4. This is what I want you to do: Get in pairs and one person pick up supplies.
Fill the cup to the rim with water. Take turns sliding (don’t drop) the
pennies into the cup. Count the pennies as you slide them in and observe the
water, the cup, and the pennies. Continue this until the water drops onto paper.
Record how many pennies you put in the water. Think about what you found out.
Draw a picture showing what you observed and how it changed as you added the
pennies.
5. Let the students do the experiment and when they are done bring the class
back together.
6. Ask them to describe what happened.
7. Probe to see if any one observed that the water at the top of the container
was swelling higher than the rim of the container. If they didn’t you may
want to talk about how scientists need to be good observers and if they don’t
understand the results the first time they do an experiment, then they will
do it again and try to observe better.
8. When the students have observed that the surface of the water rises above
the rim ask them why they think that happens.
9. Ask why doesn’t the water keep on rising above the rim?
10. What eventually makes the water fall?
11. Ask them how they worked as scientists today.
12. Ask them if they changed their minds about what would happen and what happened.
Explain that scientists do too and that they look at all their results and conclusions
as tentative.
13. Ask them how they might use what they learned today later.
Extensions:
Try this activity with soapy water or oil. Use paper clips to drop in instead
of pennies. Do you get the same results?
Activity Two
Surfin’ Surface Tension
Materials: Clean dry baking pan (13x9x2in), 1 White business-size envelope,
Clear Tape, 7 small metal paper clips (new), 1 plastic or paper cup (8oz), pencil,
blunt-tip scissors, 2 cotton swabs, and liquid dish detergent.
1. Ask students if bugs can walk on water? As them to explain why it is possible
or impossible.
2. Tell them instead of using bugs that they will create a skier to test their
guesses.
3. Show them what they will be doing: First fill the plastic cup full of water
and get three paper clips. Hold the paper clip horizontal and place it onto
the water. Dry it off between tries. Keep trying until the paper clip stays
on top of the water.
4. Ask them what they had to do to get the paper clip to float.
5. Ask them what held the paper clip on the top of the water?
6. Ask if they observed the surface of the water. If so what did it look like.
7. If not tell them that they might want to for this next part.
8. Tell the students the directions for making the skier and putting it onto
the water.
9. Have students open the envelope so it can be used like a regular piece of
paper. 10. Make the water skier (and bend the feet up so they can sit on the
paper clip. Next roll four small pieces of the tape with the sticky side out.
Then stick a piece of rolled tape to the middle of each paper clip, and place
the skier on the tape. After that fill the baking pan half-full of water. Hold
one of the skiers by the head and carefully place it into the water. Now place
a finger in the water behind the skier and gently push it along the surface
of the water. Observe how the water looks around the skier.
11. Discuss with the class about what they observed.
12. Ask what their observations suggest
13. Ask how this might explain how bugs can walk on water.
14. Ask what do scientist do when they don’t understand something. Or if
they think that they don’t have the right answers (they try and try until
they believe they understand).
15. Ask them how they could use what they learned.
Extension:
Have the students race their skiers across the water by gently blowing on the
skiers. Set up some rules for the race.
Activity Three
Will it drip?
Materials: two glasses, water, and penny
1. Submerge both cups in water. Place the opening together so no water escapes.
2. Take out of water and set it upright on flat surface.
3. Ask students what will happen when you slide a penny between the glasses.
4. Slide a penny between the rims of the glasses.
5. Ask students if their predictions were right.
6. Ask students why no water escaped when the penny was slid between the glasses.Extensions:
Try this activity with soapy water. Do you get the same results?
Activity Four
How to give pepper some PEP!
Materials: 2-8oz cups or small bowls, black pepper, baby powder, and liquid
dish detergent.
Safety Tip: Pepper and baby powder can irritate eyes, nose, and throat. Shake
both of them away from your face.
1. Fill the cup with water and cover the surface of the water with a thin layer
of paper.
2. Place a drop of detergent in the middle of the pepper.
3. Have students describe what happened.
4. If students need probing ask questions like "Did the pepper sink or
did it move away?" "What do you think is making the pepper move?"
5. Put a second drop of detergent in the water.
6. Discuss what happened the second time. Some questions could be "Does
the pepper do the same thing again? Why or Why not?"
7. Fill the second cup up with water and cover the surface of the water with
a thin layer of baby powder.
8. Have them add a drop of detergent.
9. Discuss and compare what happened.
10. Some questions might be: "What happens this time?" "Is it
different from the pepper?" "Why do you think it acts this way?"Extensions:
Have the students use soapy water to start with and drop more detergent in.
See what happens when this is done compared to the first time. Then they can
try dropping oil in the water.
Activity Five
Attract or Repel?
Materials: two bowls, toothpicks, cube of sugar, detergent
1. Ask the students what they think will happen in each situation.
2. Fill two bowls with water.
3. Arrange toothpicks in circles in both bowls.
4. In the center of one bowl place a sugar cube. Observe what happens.
5. In the center of the other bowl place detergent. Observe what happens.
6. Ask the students why the sugar draws the toothpicks and why the detergent
repels the toothpicks?
Extensions:
Try this activity with different types of water like soapy, dirty, or even oil.
Do the toothpicks act in the same way?
Activity Six
Boat Racing
Materials: 1 index card, blunt-tip scissors, baking pan and Liquid dish detergent
1. Using the index card have the students cut out a boat. Make sure the students
make a notch.
2. Ask the students what they think will happen when the drop of detergent is
put in the water behind the boat. Remember to get them to explain why they think
it.
3. Place the boat gently on the water and place a drop of dish detergent in
the notch.
4. Pull the class together and discuss with them what happened and why it happened.
5. You can compare it to the activity "Give your pepper some PEP!"
Make connections between the two activities.
Extension:
Have the students race their boats across the water. If the students do this
over and over, make sure the pan is very well washed out. Failure to do so will
cause the boats not to move. If this happens have the students explain why the
boats are not moving.