Surface Tension
Learn how surface tension allow water striders to walk on water!
What You Need
Activity 1: Surface Tension
- 2 paper clips
- 1 cotton swab
- Small bowl or container of water
- Dish soap
Activity 2: Water Striders
- 3 index cards
- 2 small pieces of aluminum foil
- Small bowl or container of water
- Scissors
Guide:
Safety Notes
Ensure you are familiar with Let's Talk Science's precautions with respect to safe virtual outreach to youth.
What To Do
Activity 1: Surface Tension
- Fill your bowl or container almost to the top with water.
- Rip a small corner of paper and place it under the paperclip.
- Very gently place your paperclip with paper on top of the water (like the photo). You might have to try this a few ties before the paper clip will float.
- Repeat steps 2 and 3 with the second paperclip.
- Dip the cotton swab into a little bit of dish soap.
- Dip the cotton swab with dish soap into the water.
- What happens?
Activity 2: Water Striders
- Fold the index card in half.
- Fold the edge of both sides around a third of the way up to make a small flap.
- Cut a triangle pattern into the flaps (see guide). These are the legs of your paper water strider.
- Fold the index card in half again and cut long rectangles into one end(like in the photo). These are the back legs of your paper water strider.
- Open the index card up and fold down the rectangles- your paper water strider is now ready.
- Fill a bowl or container around halfway with water. Now put the water strider in the bowl (legs down).
- What do you notice?
Discovery
Water molecules like to stick very close together- and they are even closer together on the surface where the water meets the air. At the surface, the water molecules are so tightly knit together that they make up a layer that is like plastic wrap (or skin). This really tight layer is able to hold things up that would usually sink in water. This is called surface tension. This is why the paper clips are able to float on the water!
Dish soap changes the surface of the water so that it is not as tightly knit as before. This is why the paper clips no longer float on the water!
Water striders are insects that can walk on water! They are able to stay afloat due to surface tension. Their long legs allow them to spread their weight out on the surface of the water. They use that special tight layer on the surface of the water to hold themselves up and walk on water.
Do some experimenting!
- Use the other index cards to make different shapes and sizes of legs for the water strider. Test them in your bowl of water and see what happens!
- Try building water striders with the aluminum foil.
- Do you notice a difference?
Guide:
What's Happening?
Water molecules like to stick very close together- and they are even closer together on the surface where the water meets the air. At the surface, the water molecules are so tightly knit together that they make up a layer that is like plastic wrap (or skin). This really tight layer is able to hold things up that would usually sink in water. This is called surface tension. This is why the paper clips are able to float on the water!
Dish soap changes the surface of the water so that it is not as tightly knit as before. This is why the paper clips no longer float on the water!
Water striders are insects that can walk on water! They are able to stay afloat due to surface tension. Their long legs allow them to spread their weight out on the surface of the water. They use that special tight layer on the surface of the water to hold themselves up and walk on water.
Investigate Further
Do some experimenting!
- Use the other index cards to make different shapes and sizes of legs for the water strider. Test them in your bowl of water and see what happens!
- Try building water striders with the aluminum foil.
- Do you notice a difference?