 Hi and welcome to Do Try This at Home, brought to you by the Institute of Physics. We're making these films to help parents and carers across the UK and Ireland get their kids curious and excited about science, even when you can't leave the house. My name's Jenny, welcome to my home. The demo I'm going to show you today is called the wobbly stick challenge. You don't need a lot of stuff for this demo. You need something long, ideally over about 50 centimetres. We had a look around our house and this is the type of things that we found. A garden cane, a strut of wood from some piece of furniture that we took apart some time ago. If you can't find anything suitable you could even make your own long stick by rolling two sheets of paper together twice and then sticking it together with some cellotape. You'll also need something to add mass to the end of your stick. So this is some play-doh that we made at home. You could use some plasticine or even a lump of blue tack. So to set up your challenge you just need to put the play-doh on one end of the stick and you're ready to go. Now you can challenge your family to the world premiere of the IOP Balance Off. Contestant number one, AJ, with a superior sense of balance and style. Contestant number two, Cab de Beste, has always dreamt of winning a back garden balance off. Round one. Each contestant must keep the plasticine at the bottom and balance the stick on the tips of their fingers. The longest time is the winner. Three, two, one, balance. Two. Each contestant must balance again but this time with the plasticine at the top of the stick. Three, two, one, balance. Excellent effort from both contestants. Our Balance Off shows that it's easier to balance the stick the further the blob of clay is from your hand. But what's going on here and how can you explain it to your family? For the stick to stay balanced you need to keep your hand directly under the mass, the piece of play-doh. Gravity is pulling down on this piece of play-doh and your hand is pushing directly upwards to counteract that force but this can't last forever. As soon as the stick starts to tip over gravity is still acting on the play-doh causing the stick to tip over more and more faster and faster. To get it balanced again you need to move your hand directly under the piece of play-doh. You'll have discovered in the Balance Off the stick moves more slowly when the mass is at the top of the stick but why is this? So you can try waving the stick and you'll find it's much easier to wave when the mass is near your hand. If the rod tips over when the mass is at the bottom it only has a short way to move but when the mass is at the top it has further to move which takes longer giving you more time to move your hand underneath the play-doh again. Think of pushing someone on a swing. If something is difficult to start moving we say it has a lot of inertia. It's much harder to start a heavy person swinging than a light person. A heavy person has more inertia. Still in the playground it's much harder to push the heavy person round, the roundabout, if they stand near the edge there's more inertia than if they sit at the middle. In the same way moving the lump of modelling clay so that it's further away from your hand gives it more inertia. The stick tips more slowly and it's easier to keep balance. Don't worry if you're not too sure about the science. The most important thing is to try it out and have fun together, test different things out and then if you need to look it up together afterwards. Thanks for watching, have fun, goodbye.