Floating, Diving Paper Clip

Safety

  • Make sure you have an adult helping you
  • Make sure you’re in a place where it’s ok if water spills

Supplies

  • A cup
  • A paperclip
  • Liquid soap
  • Tap water

Directions

  1. Fill up the cup so that the water makes a slight dome over the top.
  2. Hold your paperclip flat against the edge of the cup and carefully slide it toward the middle of the cup. The paperclip should be floating on top of the water!
  3. Once you have the paperclip floating on the cup of water, you can make it dive to the bottom of the cup! Here’s how: put a drop of liquid soap into the water.

Observations

  • How do you think the water is keeping the paperclip from sinking?
  • What happens if you put the paperclip on the water by a different method?
  • Does it still float if you just drop it on the water from above?
  • How big of a paperclip can you float?
  • Can you float another paperclip on the water after you added the soap?
  • Does the temperature of the water make a difference?
  • Can you get the water to form a dome again if you add a little more water?
  • How many paperclips can you float at a time?

What’s happening?!?

Water is a polar chemical. That means that at different ends of the molecule, it has positive and negative charges. Have you heard the saying “opposites attract?” The water molecules arrange themselves so that the positive end of one is next to the negative end of another molecule of water (see the picture below). The attraction between the polar water molecules (called intermolecular forces) is responsible for what is called surface tension. This is what allows you to overfill the cup without the water spilling out. The surface tension of water is strong enough to even support a paperclip! When you put the soap into the water, it disrupts the order of the water molecules. They aren’t lined up positive to negative anymore so the intermolecular forces are weaker than before you added the soap. The surface tension isn’t strong enough to support the weight of the paperclip, so the paperclip falls into the water just as quickly as if you had dropped it into the cup.

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