 Hello! Hi! Ready? Hello and welcome to Do Try This At Home from the Institute of Physics. We're making these videos for parents and carers across the UK and Ireland so that you can explore science together with your kids at home. My name's Tash and this one's called Reversing Arrow. And I love this one. Not only is it because it's about light, which is my specialty subject, but also once you get the hang of it, you can really get creative with it. What you're going to need is two sheets of paper, a marker pen, a tall drinks glass and some water. First off, draw some arrows on the paper. Make them about the same width of the glass. Then follow the paper to stand your arrows up. Paste another sheet of paper in front of it. Put the glass in front of that. And if you're doing this for someone in the house, it might be useful to set up a chair where they're going to be sitting. If you're doing it over the web, get your webcam ready and position that over here. And then I'm just going to adjust everything so it's lined up with a webcam. And then fill the glass with water so that the bottom arrow is under the water. Adjust the position of the glass so that the arrow is about the same size. And I'm just going to move the arrows back here as well. And it looks about right to me. Yes. Then mark the position of the glass using a pen. So now you're set up. Pour the water way back into the bottle. Put the glass back into position and then you're ready to do your trick. So I'm just going to call my niece on the webcam. Hello. Hi. Ready? What's going on here and how do you explain it to your family? Well, you start with a pencil. A pencil normally looks a little bit like this. We see it because the light bounces off it and travels in a straight line to your eye. Now if I put the pencil in the water, you'll see that it looks bent because the light changes direction as it travels from the water to the air. A similar thing happens in a reversing arrow trick. Without water in the way, we see the arrow as it is. This is because light spreads out in all directions and some of it will travel in a straight line to the webcam over here. When there is water in the way, the light bends. Light from the tip of the arrow changes direction here and here and clicks at this point before spreading out again. Same thing happens to the light from the tail collecting to this point. Because the light from the tip is now spreading from here and the tail from here, the arrow looks reversed to anyone viewing from the webcam over here. Don't worry if you don't completely get a science. Enjoy the trick. And once you've had fun with reversing arrow, you can also have fun with numbers and letters. What's it say, Saf? And once your family get the idea, they can go off and invent their own version. Excellent. If you like this video, give it a like. Or why not go over to our website for other things you definitely should try out. It is goodbye from me and goodbye from Saf.