 total success. Hello, welcome to Do Try This at Home, brought to you by the Institute of Physics. We're making these videos because we want parents and carers all the way around the UK and Ireland to be able to get their kids really excited and curious about the world around them, even if you can't leave the house. My name is Imogen and you might be thinking, Imogen, what are you doing in your bathroom? The reason is this is not my bathroom. I'm staying with my in-laws at the moment and this trick has got the potential to go a bit wrong. So I'm presenting from somewhere nice and waterproof. This trick is called the waterproof hanky and I love it. The first thing you're going to need is a glass. The next thing you're going to need is a hanky. Now I don't actually have a hanky so I am using one of these cleaning cloths. Don't use a paper hanky or a kitchen roll, it will not work. I speak from experience. The next thing you're going to need is a plate and finally you're going to need a source of water. The first step is to prove to your family that your hanky is not waterproof at all. So what you want to do is just drape your hanky nice and loosely over the top of your glass and then pour water through it. You're aiming to get your glass half full. The next step is to show to your family that the hanky can be made waterproof. So what you need to do is now stretch it over the mouth of your glass. If you're doing this trick with your family you might want to get slightly smaller glasses so they can get a really good kind of grip on the material around the outside. Then put your plate on top and you're going to aim to flip your glass hanky plate combination in one really quick motion so that it's completely upside down. You should be able to take it away and the water does not leak out. Once you've practiced this a few times bring it to the help of a volunteer. Sam can I borrow you for a second? What are we doing? Take your glass and your plate put it over the top and remembering to keep that cloth pulled nice and tight flip the whole thing over your totally willing volunteer's head and then take away the plate. What's going on here and how can you explain it to your family? If you look at your hanky really closely there are loads of teeny tiny holes in the cloth. This lets the water travel through it and air go through it as well. Now get your hanky nice and wet. Can you go through it? It's actually much much harder and that is because we have water blocking up all of those tiny tiny holes so for the air to go through it's got to push the water out of the way and that's actually pretty difficult. How can water block the holes? I hear you crying. Have a look at this picture. The surface of the water looks like it's covered in a stretchy skin almost like the surface of a balloon. This effect is called surface tension and that surface tension is strong enough to be able to hold up my pond skater so it doesn't sink. It's also a really cool thing that you can try out with your family with this paperclip. With a glass of water that's completely full the surface tension over the top is strong enough to be able to hold up something that should sink like a paperclip and as soon as we break that surface tension my paperclip sinks to the bottom. Surface tension is a bit like a balloon stretched over a hole. With a big hole then my surface is easy to push and with a small hole it's much harder to push. Now with a glass of water without a hanky when I flip it over the surface tension is nowhere near strong enough. It breaks easily across the large mouth of the glass and the water pours out. When I add the hanky water sucks into the hanky and blocks the holes in my cloth. Because the holes are smaller the surface tension skin across each hole is stronger and actually gets strong enough to be able to keep the water inside of my glass which is why my hanky becomes waterproof your family stays dry and you stay friends with your family. If you're not totally sure about the science don't worry. Investigate with your family maybe look it up with your family if you need to and have fun along the way. Have a lovely day and see you next time.