See if you can avoid getting wet in this water and clingfilm challenge!

What to do:

1. Pour water into a beaker until it is about 3/4 full and give it to your friend.
2. Rip a piece of clingfilm off the roll that's about 15cm long.
3. Put this piece of clingfilm over the opening of the water-filled beaker, making sure that it's pulled tight and it's firmly stuck to the sides of the beaker.
4. Your friend can now (carefully) turn the beaker upside down. The water should stay in the beaker.
5. If water is spilling out, turn the beaker the right way up, stick the clingfilm down a bit more and then try again.
6. With one friend holding the beaker upside down, sit another friend underneath the upturned beaker.
7. Now you and the friend that's left can take the pencils and take it in turns to stab the clingfilm covering the beaker (it works best if you stab the clingfilm quickly, swiftly removing the pencil). A few drops of water may come out each time, but then the water should stop dripping.

8. Keep going.
9. After a few goes there will come a point where the water won't stop and will keep on glugging out on to your friend! Whoever made the hole that makes this happen loses!

Here we see surface tension in action. Water has a high surface tension and this means the surface of water has a sort of invisible skin on it, pulling it back into the container. Surface tension is so strong that it can hold water together even across a hole, which is why even when you make holes in the clingfilm the water doesn't all come pouring out.

But this is only half of the story; the other half is to do with air. For the water to get out, air must be able to get in. So when small holes are made in the clingfilm only a small amount of air is allowed in, which is why only a few drops of water fall out. It is only when a hole is made in the clingfilm that is large enough for lots of air to get into the beaker that all the water can come rushing out.