# Investigation Sequence

## Title

SurfaceTension

Megan Rang & Karmen Hughes

Date

## Focus Questions

What is surface tension?
What is cohesion?
What happens to water molecules due to surface tension?
Why do some liquids have more surface tension than others?
How can one break surface tension?
How can you create stronger surface tension?
How can you create weaker surface tension?

## Concepts

### Cross cutting concepts

Explanations tell how something does what it does.
Explanations are based on observation derived from experience or experimentation and are understandable.

## Background information

Surface tension is caused by the force per unit of area on the surface of the liquid due to the cohesion of the liquid. All liquids have surface tension, but some have more than others. The ones that bead up like water have more surface tension and the flatter ones have less. Adding a variable can change surface tension.

## Activity Sequence

1. Surface Tension Pamela S. Moy
2. Surface Tension-Lisa C. Ingram
3. Surface Tension-Lisa C. Ingram
4. Surface Tension-Lisa C. Ingram
5. Sticky Penny Experiment
6. Surface Tension Amina Grant
7. Surface Tension Amina Grant
8. Surface tension on coins
9. Surface tension on coins
10. Surface Tension (Soap Boat)

## Activity Descriptions

Activity 1
Surface Tension
Materials:
One hot plate to preheat a large beaker of hot water (for all to use), (For each group), Six small clear plastic cups, eyedroppers, Water, Two boxes of paper clips, Dishwashing liquid, Paper towels, Black pen for labeling
Procedure:
1. Ask students what will happen if they fill a cup with water and add paper clips.
2. Ask them about how many clips it would take before it would overflow.
3. Tell them that they are going to do just that with hot water, cold water, and with hot and cold soapy water.
4. Ask them what they think the difference will be if any,
5. Give the following directions to all students. Tell them that they need to get four cups. Two to fill with tap water and two with the hot water (near boiling) CAUTION them on how to handle hot water. Tell them to take almost fill up the cup and a little bit more in a second cup. When they get to their station they can use an eyedropper to fill it to the rim.
6. Tell them that one of the cups with tap water they will need to fill it so the water is exactly to the rim of the cup without spilling over the side. Then they are to drop one clip at a time carefully into this cup until they see the water begin to seep over the side. Then count the number of clips it takes to cause this to occur. Record this number in a chart and describe the dome of water building on top of the cup.
7. In the second cup with tap water fill it to the rim, add five drops of dishwashing detergent, allow about a minute for it to disperse in the water, and repeat the process you used with the first cup. Count the number of clips required to cause the water to seep overt the side. Record this in a chart and describe the dome of water building on top of the cup.
8. Fill the third cup with the hot water (Be very careful not to burn yourself with the hot water or the hot container.) Make sure you get the water level to the rim as you did before. Add five drops of dishwashing soap, allow about a minute for it to disperse in the water, add clips until water overflows. Describe the dome. Record this information.
9. Fill the fourth cup with the hot water (Be very careful not to burn yourself with the hot water or the hot container.) Make sure you get the water level to the rim as you did before and add clips until water overflows. Describe the dome. Record this information.
10. Write a summary of these directions on the board, assign groups and begin the experimenting.
11. Bring the class back together and have them record their data on a chart on the board.
12. Ask each group to explain their data for the four experiments.
13. Ask them what happened to the surface in each of the four different cups.
14. Ask them to explain why there was or wasn’t a difference.
15. Ask them how they can use their observations to support their reasons.
16. Ask them where they could use the information that they discovered.
17. How would a scientist use it?

Activity 2, 3, & 4
Surface Tension
Materials:
Overhead projector, 2 glasses of equal size and depth, A bucket, Water, Pennies (60 per group or person), A box of toothpicks, Liquid soap or detergent, A box or cub of sugar, Clear cups (1 per group or person), Bubble solution, Bubble wands or other bubble instruments
Procedure:
1. Ask students to brainstorm what surface and tension mean.
2. Discuss where they have heard the words before.
3. Write all comments on the blackboard.
4. Describe each of the following experiments to the students.
5. Fill two glasses underwater, hold them rim-to-rim so no water escapes, raise them above the water level, and stand the glasses on a flat surface so that one rests upside down on top of the other. Students are to try to slide one penny between the two rims.
6. Put enough water in a bowl of water so that you can float toothpicks in a circle. Then put a cube of sugar in the center of the circle. Get another bowl and arrange the toothpicks in a circle again. This time place a piece of soap or liquid detergent in the center.
7. Fill a cup to the rim with water and add a drop of food coloring. Place the cup on top of a white piece of paper. Slide pennies into the colored water counting them, until the colored water drips onto the paper.
8. "Why does it take so long for the water to drip?' (Answer: Surface tension builds around the cup, until it is broken with the penny.) Have students formulate an answer within the groups. Discuss the answers as a class.
9. Ask the students what they learned from the experiments.
10. Ask them to support their conclusions with observable evidence.
11. Ask why the water didn’t leak from the two glasses. (The molecules are pulling and stretching, but not far enough to break the skin of water. Thus no water can get out, unless the surface tension is broken.)
12. Ask them what happened with the toothpicks (observation). (The toothpicks went toward the sugar and they went away from the detergent.)
13. Ask they why the think that happened (The sugar sucks up water, creating a current that carries the toothpicks with it toward the center. The soap is an oily film that spreads outward. It weakens the surface tension, and the film carries the toothpicks away with it.).
14. Ask them how this information can be used to help people. (Soap reduces the surface tension between dirt and the fabric, soap or other similar chemicals are used in dyes, insecticides, and herbicides to allow them to spread out and cover a greater area.)
15. Ask them how scientist can use this information.

Activity 5
Sticky Penny Experiment
Materials:
(For each group or person), Penny, Eye dropper, Paper towel
Procedure:
1. Ask students how many drops of water will stay on the penny before water spills over.
2. Have students write predictions on the board.
3. Give students the following directions:
4. Place a penny on a paper towel on top of a table. One person can fill the eyedropper with water and then begin dropping water onto the penny one drop at a time. The second person should count and write down the numbers of drops. Stop dripping the water when it spills over the sides of the penny. Repeat this experiment, but make sure the penny is dry before beginning again.
5. Ask the students why the water stays on top of the penny.
6. Have groups formulate ideas.

Activity 6 & 7
Surface Tension
Materials:
Overhead, Beaker, Straight pins, Water, Wire (24 cm long to make a cradle for a straight pin), Medicine-cups (to hold 1 part dishwashing detergent), Water soluble pens, Liquid detergent & Glycerin, Square wire frame (use the same wire from cradle)
Procedure:
1. What will happen when one drops the straight pin vertically into the water.
2. What will happen when one drops the straight pin horizontally into the water.
3. Make predictions
4. Give students the following directions:
5. Fill the beaker with water, (each student has his own beaker and straight pin.) Take the straight pin and show that it is not possible to float a straight pin on the water when it is dropped vertically into the water. Fish straight pin out of the water and dry it off or use another pin. Now hold the pin horizontally as close as possible to the surface of the water (without touching the water) and drop it.
6. What were the differences between the vertical and horizontal drop.
7. Discuss outcomes as a class.
Experiment 2
1. What will happen to the thread in a soap solution.
2. Write predictions on the board.
3. Give students the following directions:
4. Make a soap solution by mixing the following liquids: 1 part dishwashing detergent, 1/2 parts glycerin, and 3 parts water. Place this soap solution in the shallow container, make a soap film by dipping the wire frame in the solution and taking it slowly out. Make a small loop of thread (diam. 3-4 cm), wet it in the soap solution and lay it carefully in the soap film. Once the thread loop lies in the soap film, pierce the center of the loop with the dry object (pencil or dry finger). Slant the wire frame, wiggle it, and observe the perfect thread circle move and travel throughout the whole frame.
5. What happened to the thread.
6. Discuss why this occurred.

Activity 8 & 9
Surface tension on coins
Materials:
Coins: Pennies, nickels, dimes, quarters, (half dollar or silver dollar if available). Eyedroppers, Water in a bottle, Soapy water in a bottle, Paper towels
1. Predict how many drops of water each coin will hold.
2. Write predictions on the board.
3. Give the students the following directions:
Experiment A
1. The students should get their bag of coins. They should then place a coin on a paper towel and begin dropping water on the coin until the water overflows. They should record how many drops the coin held before the water overflows. This number should be placed under a heading called "Plain Water." This should be repeated with the remainder of the coins.
2. Discuss the number of drops that each coin holds.
3. Discuss why different coins hold more water.
Experiment B
1. Predict how many drops of soapy water the coins will hold.
2. Write predictions on the board.
3. Give the students the following directions:
4. The students should get their bag of coins. They should then place a coin on a paper towel and begin dropping soapy water on the coin until the water overflows. They should record how many drops the coin held before the water overflows. This number should be placed under a heading called "Soapy Water." This should be repeated with the remainder of the coins.
5. Discuss the number of drops each coin holds.
6. Discuss the difference between the soapy water and tap water.

Activity 10
Surface Tension (Soap Boat)
Materials:
Index card, any size, Scissors, Liquid soap, Clean water, Clean 9" pie tin or other container
1. How can one use surface tension to make the boat move.
2. Will different soaps make the boat move faster.
3. Give the students the following directions:
4. Fill the pie tine half full of water and have it sitting on the front table when the students come in. Cut a triangle out of the index card (2" high and 1" wide should do it.) Hold it up to the students and tell them that it is a boat. Cut a smaller triangle out of the bottom of the boat. Tell the students that this is where the motor goes. Place your boat in the water near the edge of the pie tin. It will not go anywhere. Next, remove the boat from the water. Place a drop of the liquid detergent on your finger and touch it just inside the V notch of the boat. Gently place the boat back in the pan of water, soapy side down, and it will jet across the surface much to the delight and amazement of all involved. Have the students try the process themselves. They should have a fun time. Students could try different types of soaps, and both warm and cold water. Students could try different boat styles to see which kind goes faster.
5. Discuss what made the boats move the fastest.
6. Discuss why this happened.