It’s been a while coming, so many other things to write about! But this is the second in the Playground Series on science children encounter around them. Slides are about gravity, potential energy and friction. They’re also about fun, and we play with them regularly – as well as people, there are all sorts of interesting things you can send down a slide!
Gravity we all know about, it is the force pulling us into the earth. It pulls the same on everything, no matter how big or small it is – 9.8 metres per second per second. That’s not a mistake, gravity isn’t measured as a speed but an acceleration – the longer you fall the faster you get. So if it was just about gravity everyone would go down a slide at the same rate. But slides aren’t falling they have friction involved as well, which slows things down. In the video we sent several things down the slide and saw how far they went, the differences come down to friction.
Believe it or not, slides are machines for converting energy. Energy changes between kinetic, or movement, and potential energy. Potential energy is stored energy – it is the potential something has to move, like a stretched elastic band. When you climb up a slide you are using kinetic energy and turning it into potential energy, height. At the top of the slide you have lots of potential energy and no kinetic energy, but then as you go down it changes so you have more and more movement and less and less potential, until at the bottom it is all movement and no potential. We played around with this by pushing things up the slide. They go up, slow down and pause, then come back down again. Once again, you can see the variation in friction affecting how far they go. This is because it takes energy to overcome friction, so if more of the energy is going in to that there is less available for going up and down.
Finally friction, after seeing how it controls everything else! Friction is all about microscopic bumps catching on each other, if you put one hand on top of the other and push you will see it in action. The three objects we’ve been using have different strengths of friction because of the size of their bumps. A ball has very low friction because it rolls, not slides, so the bumps don’t get stuck. The long, silky hairs of the teddy bear are very smooth and can move apart to go around things, so it only has medium friction. The doll clothes not only have fairly large bumps because of the threads, but they are very loose and bunched up which makes more bumps so they have a lot of friction.
When you are walking up a slide you need friction to help you fight the gravity pulling you down. The sand where we were filming was wet and sticky, but between the shoes and the slide it acted as tiny rollers or ball bearings. This meant Molly was trying to roller skate up the slide, which wasn’t going to work. Bare feet with sand would have the same problem a bit, but not as much because the sand can dig into the skin of feet which holds it steady. For clean shoes the main factor is the size of the tread – a large tread pattern like on running shoes tends to have big smooth patches without many bumps. The best thing is clean bare feet, because you have a fantastic pattern on your feet just like fingerprints. In fact climbing is the reason it exists – our feet were originally used for climbing trees then for scrambling on rocks, both things that are a lot more like climbing up a slide than walking around in shoes. So the ridges on your feet are just the right size to cause lots of friction and help you climb. Personally I think the best playground toy would be a square platform with 4 slides coming off it, so everyone can climb up them!
Did you notice the suggestion from Molly? That’s experimentation in action! She’s observed that she’s falling down and predicting that bare feet might work better, then wanting to try them. A mini P.O.E!
There’s a lot more to do on a slide than just sit on it and slide down, we haven’t even looked at all the different ways you can sit and lie and how your clothes change it, and all the different toys you can use on them. What can you do on a slide? This post is part of We Play at Childhood 101.
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