Floating Paperclips

Paperclips floating on water. How many will you get to float?

This experiment will explore the properties of surface tension and cohesion. Surface tension is the property of water that makes water act like a stretchy skin, making it resist an external force. This is why a water strider can walk on water with ease. Water's high surface tension is caused by the cohesion of water molecules. The water molecules pull on each other. Cohesion is when water molecules stick to each other. This attraction causes the top layer of water that meets the air to be elastic-like and strong, creating this high surface tension. This lab will show how surface tension is able to float paperclips.

Materials:

• Paperclips

• Clear, plastic cups

• Water

• Squirt tube filled with rubbing alcohol

• Squirt tube filled with water

• Plastic tray (To keep work area less wet and messy)

Procedure:

1.  Place a plastic cup on a tray and fill it up with water all the way to the top of the rim. Now using a tube with a squirt spout, slowly top it off with more water until a rounded surface forms. Stop adding water once you have a rounded surface slightly above the rim of the cup. Do not let the water run over the cup.

2. Now take a paperclip and carefully slide it over the rim of the cup and gently onto the rounded surface of water. Make sure the paperclip is dry. If wet, dry it off well with a paper towel. Observe what happens. Students will write this in their science notebook.

3.  See if you can add more paperclips, carefully adding them in the same way as the first one. 

4. Once you have done steps 1-3, try it again, but this time forcefully throw in the paperclip.

Observe what happens.  

5. Using a new cup, fill it to the top of the glass with water again, only this time top it off with rubbing alcohol instead of water until a rounded surface forms. Now students will try and place a paperclip gently over the rim and directly on the top of the water. They will record their observations in their science notebook.

What other property of water is being observed in this picture other than surface tension?

Student Questions:

1. If a paper clip is denser than water, how is it able to float on top of water?

2. How many paperclips were you able to float on the water when it was only water?

3. What happened when you added an alcohol layer to the water?

4. Define surface tension and cohesion.

 Extension:

*Try adding drops of dish soap to a cup filled over the brim with water. What happens when you do this? Why?