You wouldn’t think that a handkerchief or a cleaning cloth would make a particularly effective ‘plug’ to stop water pouring out from a glass held upside down. But if you’ve just watched someone on TikTok carrying out this experiment then you’ll know that they really can!

Here comes the science

When you usually turn a glass of water upside down gravity pulls down on the water which makes it pour out of the glass. But in our experiment, other invisible forces – upward air pressure and surface tension – stop the water from coming out of the glass. Air pressure pushes on everything, so pushes up through the mouth of the upside down glass. Surface tension is what gives water an elastic-like skin.You know how you can overfill a glass just above the top without it spilling? Well, that’s surface tension.

The strength of surface tension varies. The smaller the stretch of water across a gap, the stronger the surface tension. Without a cloth, the hole at the top of a glass is large and the strength of the surface tension and upward forces of air pressure aren’t big enough to beat the downward force of gravity.

But when you place a cloth – which has loads of tiny holes in it – across the top of the glass, the holes through which water has to go are much smaller so the surface tension is a lot stronger. This super strong surface tension, combined with the upward push of air pressure, is large enough to balance the force of gravity and keep the water inside the glass. There’s no real magic at play here but there are some amazing things going on which can be explained by physics!!

Want to experiment more?
If you liked this Waterproof Cloth trick then you’re well on your way to becoming a physicist. You can also watch our TikTokers carry out an amazing eggsperiment in any of the links below. And there are loads more experiments that you can try at home by watching these videos on YouTube

We think of eggs as being fragile. They easily crack on the side of the pan. And if you drop one it will smash. So it’s surprising when someone stands on them and they don’t just collapse into a messy gunge of broken shells.

Reason #2.
An egg will crack if you tap it on a pan but it is super strong if you try to squash it along its length. This is because eggs are dome-shaped and domes are particularly strong structures.

People have known this for thousands of years and it’s the reason why you see so many domes in old buildings. A dome directs the forces along the length of the material, (literally) playing to its strength. Also, because a dome forms a complete circle, it spreads the load evenly and prevents it from being concentrated in any small areas – stopping anything from cracking. Pretty amazing don’t you think!