Surface tension is weakened by different materials.
Scientists create questions, design an experiment, and use observations to
answer their questions.
All scientific ideas are tentative and subject to change and improvement.
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.
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 (dont 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 didnt you may want to talk about how scientists need to be good observers and if they dont 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 doesnt 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.
Try this activity with soapy water or oil. Use paper clips to drop in instead of pennies. Do you get the same results?
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 dont understand something. Or if they think that they dont have the right answers (they try and try until they believe they understand).
15. Ask them how they could use what they learned.
Have the students race their skiers across the water by gently blowing on the skiers. Set up some rules for the race.
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?
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
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.
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?
Try this activity with different types of water like soapy, dirty, or even oil. Do the toothpicks act in the same way?
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.
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.