Things that are more dense than water – like paperclips – sink in water. If you give this a go you will quickly see your paperclips sinking to the bottom of a glass of water.

This video shows you how you can use science to trick those pesky paperclips into floating. Then, you can impress your friends by showing them your successfully floating paperclips and get them to have a go.

How does it work?

The molecules within a liquid are all attracted to each other by cohesive intermolecular forces. The molecules at the surface of a body of water have no water molecules above them. As a result they are more strongly attracted to the water molecules beside and beneath them. This causes a phenomenon called surface tension.

The surface tension means that the surface layer of water is more resistant to external forces than the water beneath it. By resting the paperclip on tissue paper at the surface of the water you are able use this high surface tension to support the paperclip and stop it from sinking to the bottom of your glass.

For this activity all you need :

• a shallow bowl
• water
• ground pepper
• washing-up liquid

The video below shows you how to achieve this mesmerizing trick.

How does it work?

The surface tension that allowed us to float paperclips in the previous science trick is also playing an important role here. Surface tension causes the surface of water to dome upwards slightly. You can see this if you overfill a glass of water without it spilling.

Detergents like washing up liquid and soap are part of a chemical family called surfactants. When used in low concentrations these work to reduce the surface tension of water, causing the water molecules to relax and spread out. By floating pepper on the surface of the water you are able to see this spreading out effect as the pepper is transported towards the edge of the plate or glass.

You can combine the last two tricks by using washing up liquid to make the paper clip you made float, sink again. Watch the video to see how it is done.

How does it work?

The science explanation is the same as the previous trick – the washing up liquid reduces the surface tension of the water causing the water molecules to spread out.

You will need:

• A coin
• A dish of water
• A glass
• 4 matches
• Some Plasticine or Blu Tak

Start by placing a coin in a dish of water and asking your friends to try and get the coin out without getting wet fingers or spilling any water.

When you have finished watching them struggle, you can impress them by removing the water from around the coin using science. Watch the video to find out how.

How does it work?

Soon after you cover the lit matches with the glass they go out and the water is drawn up into the glass. This sequence of events holds the key to the science that is taking place.

When you first cover the matches the fire heats up the air inside the glass and it expands. The glass restricts the amount of available oxygen, needed to keep the matches alight and soon the matches go out. Without the flames there is no heat source and the air starts to cool down and contract. This draws the water from the dish into the glass allowing you to remove the coin without getting wet fingers.