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Paperclip Float

Scratch below the surface to float on water

Australian Curriculum links

  • Science > Chemical Sciences > Year 4 > ACSSU074
  • Science > Chemical Sciences > Year 6 > ACSSU095

You’ll need

  • 2 paper clips
  • Bowl of water
  • Detergent

What to do

  1. Rest a paper clip on the surface of the water.
  2. Make sure the paper clip is lying flat and straight.
  3. Look closely at the surface of the water. Is the surface bent from the weight of the paper clip?
  4. Add a drop of detergent to the water. What happens to the paper clip?
  5. What happens to the surface of the water?

Note: To repeat the experiment, the detergent will need to be thoroughly rinsed from the container.

What’s happening?

An unravelled paper clip can be used as a handle to lower another paper clip slowly and gently onto the water.

Water has a high surface tension, which means that each molecule (or tiny piece) of water is very attracted to the water around it, and wants to ‘hold on’ tightly to the surrounding water. This means that the outside of the water acts a little like a skin.

The surface tension of water is strong enough to hold the paper clip on top of the water. Some small insects such as mosquitoes are able to walk on water because of high surface tension.

Adding detergent to water lowers the surface tension, because it interferes with the water’s ability to hold tightly to itself.

When detergent is placed in the water, the surrounding water pulls away from the detergent. This is a little bit like a line of people holding hands and pulling tightly out on each other. If two people in the middle of the line let go of each other’s hands, the rest of the lines falls away from the point at which the chain was broken. As the water’s ‘skin’ breaks, the paperclip sinks.