 Hello, and welcome to Do Try This at Home, brought to you by the Institute of Physics. We're making these videos because we want to help parents and carers around the UK and Ireland to get their kids excited and curious about the world around them, even when they can't leave the house. My name's Mikey and I'm still here in my front room. Luckily though, I get to make this video for you as it's about one of my favourite things, space travel. So, get ready to discover the furthest unreachable corners of your front room. To make your balloon rocket, you're going to need a balloon, you're also going to need a length of string, a straw, and I'm using a paper straw, some scissors, and some tape. So before you start, decide how long you want your string to go. That could be all the way across the room or it could just be a couple of metres. So I'm going to try and see how far I can get a piece of string within my tiny flat. So once you've found your ideal length, you need to find two secure points to tie the string to. Bear in mind it wants to be at the right height so the balloon rocket is visible for all your family and you also need to have enough strength in it so you can have enough tension that it's in a straight line. Once you've found your point, you can tie one end on, don't tie the other end on yet, then you can cut the string. Next you're going to cut the straw into two short lengths, one, two, about three centimetres inch and a half each, then thread them onto the loose end of the string. Once you have your two pieces of straw threaded onto the string, then it's time to tie it up. Next take two short lengths of tape, blow up your balloon, holding it shut at one end with your fingers, and you can actually use a clothes peg to hold this closed. I'd actually have one at home at the moment so I'm just going to pinch it. So you're going to stick your two pieces of tape in the centre to each of the two short lengths of straw threaded on your string. Now this is a fiddly bit so you might want to get someone to help you because what you're going to do is just stick the tape onto the balloon like that. Alright, now we're ready to launch. So what's actually going on here and how can you explain it to your family? A rocket is a vehicle that carries everything with it that it needs to create a force to push it forwards or in most cases upwards. So when you're filling up your rocket balloon you're giving it what it needs in order to make it self-travel, in this case air. It's actually quite hard to blow up the balloon because as you're blowing into it the balloon actually pushes back against you as you blow and it's this pushing of the air that makes the balloon move. Well that's because air is made up of particles, there are loads and loads of these particles inside the balloon. They're whizzing around in every direction creating a force and pushing or whatever they bounce off. They're hitting each other but they're also hitting the inside of the balloon. They're moving in a left and right, they're also hitting the top and bottom and these forces cancel each other out. That's what we call a balanced force and that's why the balloon doesn't move. So what happens when we open one end of the balloon? Well there's no longer particles pushing against the inside surface of this edge of the balloon because they can escape instead but they are still pushing against this side which means the left right balanced force is no longer balanced and it's this unbalanced force acting inside the balloon on this edge which causes it to move along the string. The same thing happens with real rockets except it's fuel not air but it's the same principle. Something can escape one end and therefore creates a force on the other end in the opposite direction and causes it to move. Now this is rocket science so if you're not sure just have fun with your family test it out together and if you need to look it up just look it up together. Thanks for watching this edition of Do Try This At Home and we'll see you next time.