Paperclips are usually made of metal and, since metal is typically dense, they will sink in water. However, if you are careful, you can get a paperclip to float on the water surface!
You will need:
- A container of water
- A paperclip
- Some tweezers
- A piece of tissue
How to do it:
- Place the piece of tissue on the surface of the water.
- Gently place the paperclip on the tissue.
- Use the tweezers to push the tissue under the surface and move it away from the paperclip.
- Fish out the tissue and hope the paperclip stays where it is!
How it works:
Surface tension is a surprisingly strong force and can support more weight than you might realise. The reason that the paperclip will not float if you place it on the water without the tissue is pressure. You will never be able to place the paperclip perfectly flat onto the surface.
So when you do place it, one side will be pointing down lower and contact the water first. When this happens,the weight of the paperclip as well as the force of your hand moving the object downwards all act through the relatively small area of that bit of paperclip in contact with the surface. Since pressure is a force applied over an area, the pressure is magnified by the paperclip not being level and this overcomes the resistance of the surface tension and the paperclip descends into the watery bulk. Once in the liquid, it is simply a question of density and the paperclip, being more dense than water, sinks to the bottom.
When you place the paperclip on the tissue instead, the weight of the paperclip is spread out over the whole area of the tissue, spreading the weight over a greater area of water. This means that there is more surface tension from the water holding up the tissue and the paperclip. When you carefully pull away the tissue, the paperclip can stay floating because now it is flat and there are no other forces (like your hand pushing the clip down) to encourage the clip to break through the surface. Floaty metal!
Can I break it in a fun way?
The answer to this (as always in science) is yes.
Surface tension can be disrupted by a huge number of things. If the container is not clean then the surface of the water will end up covered in dust and this
will disrupt how strong the surface tension can be. You could find out how dirty your hands are by dipping a finger (gently) into the water near the clip. If
you are too rough then you will cause ripples and those might cause the paperclip to sink but if you get it just right then the oils in your skin will spread
over the surface and decrease the surface tension until the paperclip sinks with quite a satisfying plop.
Of course, if you have oil-free skin and this does not work, you could always dip a tissue in some hand soap and then dip that tissue into the water near the clip.