Video: Levers and pivots

﻿Hi everyone, and welcome to this lesson. This is the first lesson in our forces topic. What we're going to be talking about are levers, pivots and moments. So hopefully by the end of the lesson, we'll know what all of those words mean. Before we start, I need you to get a pen, piece of paper and a calculator if you have one. So please pause the video now to go and get those. And once you've got those, please go to somewhere quiet where there aren't any distractions so that we can really focus on the lesson. You might also want to turn your mobile phone off or switch it to silent. So once you've done that, let's get going. There are going to be three parts of the lesson. The first part is talking about what a lever is and what a pivot is. So don't worry if you've never heard those words before, we're going to learn them together. The next part is talking about what a moment is and how I could make a moment bigger. The third part we're going to add in some maths and some numbers, and we are going to actually calculate the moment with an equation. And then right at the end, you can go and do an exit quiz to show how much you've learned. This is the first lesson in this topic. And you might be wondering what forces is all about. Forces is related to lots and lots of different areas of life. Pause the video now and see if you can guess what these jobs related to forces are. So these jobs are astronaut, being a builder or an engineer, a gymnast, architect, and a pilot. And I'm sure you can think of lots of other areas of life, where forces are really relevant to you. What we're going to do at the beginning is try a little mini experiment. The first thing I want you to do is find a door that's open, and what you're going to do is use one finger to push the door closed, but you need to do it as close to the edge of the door as possible. So as far away from the hinge as possible, probably near the handle, but try not to use the handle. So go have a go now. You might want to pause the video to go have a go. And now I want you to do exactly the same thing, so one finger trying to close the door, but this time push as close to the hinge as possible. So the other side of the door, so as far away from the handle as possible. So pause now and go try that. So hopefully you noticed that one of them was harder than the other, or you had to push harder on one than the other. What we're going to talk about today should hopefully explain why that is. So let's start with what a lever is. So a lever is a rigid object, for example, a bar like a plank of wood or metal. And let's say, I want to try and lift this heavy object that I've got here, my black object on the screen. So what I've got is a bar and it's balancing on my little blue triangle. And if I push down with a force on the end of my bar, what's going to happen? My bar is going to rotate. Okay. So as I push my bar rotates or it turns, okay. And if you notice, the bit or right on top of the triangle, hasn't, hasn't moved. So that has stayed the same. So this rigid bar would be called a lever. Okay. Lever. So you might want to pause now and try practising that word, lever. And the part in the middle, that the lever rotates about is called a pivot, pivot. So you might want to pause again and try saying that, pivot. So here's another example of a lever being used. My friend over here, wants to lift a really heavy box. And to do that, he is going to use a lever. So you can see that he's got a really long bar, that he is trying to use to lift the box. And he's going to push down on the lever and the lever's going to turn, and that is going to lift the box. But there's a little point there where it's balancing on the floor, that's not going to move and that's called the pivot. So the lever is the part that rotates and the pivot is what the lever is rotating about, the part that doesn't move. Here's another example, a spanner, okay, you might have seen this. So a spanner is used to do to tighten or loosen bolts. You might have seen one used before. You hold one end, you put the other end around the bolt and then you pull the end towards you, and it rotates, It turns around. And so the part that's rotating that you're pulling is going to be called the lever. And the part that doesn't move, the part that's connected to the bolt or nail is called the pivot. Another example is a wheelbarrow. A wheelbarrow is used to, to move really heavy things that we wouldn't be able to just lift on our own. And what it is, you can see that there's long handles that this farmer is using to move the wheelbarrow. And so those long handles are called the levers. And the part that doesn't rotate as the wheelbarrow is lifted is called the pivot. And in this case, that's near the wheel. So if I wanted to write down a definition for what a lever is and what a pivot is, this is what I could write. Okay. So I'll read it. A lever is a simple machine. A lever is a rigid object that will rotate around a fixed point or pivot. So it's a simple machine because we use it to help us do a job. It's a rigid object, so it's rigid. That means it's not all flexible and flappy, it's rigid and it will rotate, or it will turn about a fixed point, the point that doesn't move, which we know is called a pivot. Now it's your turn to try. Use your finger again, to point at the lever and point at the pivot. So five seconds to try doing, to do that. Okay. So the lever is the handle and the pivot is the part that's around the bolt. So really well done, if you've got that right. What about in this case, I'm trying to lift a rock? Five seconds. So the lever is the bar that's going to rotate. And the pivot is the part that doesn't move the part above the triangle. Really well done, if you've got that one right as well. Now try this one. This time, we've got two people on a seesaw. Okay. So the bar of the seesaw is the lever and the part in the middle of the seesaw that doesn't really move is the pivot. So really well done, if you've got all of those right. This one is a bit trickier. So I'll give you 10 seconds to think about this. If I was turning a tap like this, where would my lever be? And where would my pivot be? Okay, so my pivot is in the middle, 'cause it's not going to turn, but the edges that I'm pushing round are the levers. So really good if you've got that one, 'cause that one was really tricky. So here's a multiple choice question that I'd like you to try, please pause the video now and press play, when you think you know the answer. Okay. The answer is option two. It's a simple machine and a rigid object that can rotate. What does a lever rotate about? So you might want to pause the video now and have a read. The correct answer is option three, a point called a pivot. So really good if you've got that one right as well. Which point of my door handle is the pivot? I'll give you five seconds. It is B. Which point of my wheelbarrow is the pivot? It is D. So really good if you got those right as well. What I'd like you to do now is pause the video and try and answer these questions. So what are levers and pivots? So please pause the video now. So levers are simple machines. They are made from rigid objects, which rotate or turn about a point. This point is called a pivot and you spell that P I V O T in case you were wondering. So really well done if you've got those right, or if you've got some wrong, but now you know how you can improve. Okay. So as we know, we can use these forces to rotate a lever. And when, because that force is being used to rotate, we call that the moment. So it is the turning effect of a force. So as you push, the lever turns and that effect is called the moment. So the moment of the force makes the lever turn. Here's another example with the wheelbarrow. So this time we're going to lift the wheelbarrow up and it turns, it doesn't just move up, it actually rotates. So there's a moment of the force and that makes the wheelbarrow turn or rotate. So the moment is the turning effect of a force. So it's like this. Okay. So what if I am really happy? Look, I've got my force and it's got a big enough moment to lift my heavy object, my black heavy object there. What if I add another heavy object? What am I going to do? Now my force, my moment, isn't big enough to rotate or to turn my bar. What am I going to do? Well, there are two things I can do. The first thing I can do is I can just push down with a harder force with a larger force. So I could get my friends to come and help me, we could try and push down together, or maybe I could just push down a little bit harder. So first one, I could use is larger force. The second thing I could do is I could push down further from the pivot. So further from the pivot, you can see that that's what it was and that's what it is. So I've moved further away from the pivot. And we call that distance from the pivot to the force, the perpendicular distance. So this is how it's spelt, perpendicular distance. It's the same word as you would have seen in maths, but let's just practise saying it, perpendicular. Perpendicular. Perpendicular distance. So hopefully, you know how to say that really long word. Now, well done. So another example of a perpendicular distance is on the spanner. If I have a look, I've drawn a blue line from the pivot, which was the nail all the way to the force, okay? Which is where we pull the spanner. And that blue line from the pivot to the force is called the perpendicular distance. So let's just summarise. My moment is my turning effect of a force. And there are two ways I can make this bigger. Number one, I could make my force larger. Number two, I could make my perpendicular distance longer or larger. So force being larger or perpendicular distance being longer. So what advice would you give someone who was struggling to lift this rock? What I would tell them to do is either they can get a longer lever, so you can get a longer lever to use. And that will increase my perpendicular distance from my force to my pivot. The other thing he can do is ask a friend to help, and that will increase the force to have a larger force. So you can either increase the force or increase the perpendicular distance. What advice would you give someone struggling to turn this bolt? I would tell them to get a longer spanner. Hopefully you said the same thing. So if they have a longer handle, that means they can have a longer perpendicular distance, which means they will have a larger moment. So really well done if you said that. Here's another multiple choice question. So please pause the video now and press play, when you think you know the answer, The correct answer is option one. A moment is the turning effect of the force. Here's another question. This time there are two correct options. So you might want to pause the video now and have another go. The correct options are option one, increase the force and option three, increase the perpendicular distance from the force to the pivot. So really, really, really well done, if you got both of those and really well done, if you've got one of them and well done, if you now know something you didn't know before. So what I'd like to do now is pause this video and answer these two questions on a piece of paper. I'll tell you the answers. Question one, what is the moment of a force? The moment of a force is the turning the turning effect of the force. Write down two ways to increase the moment about a pivot. Question two. The first way is to have a larger force or increase the force. The second way is to have a larger perpendicular distance from the force to the pivot. So really well done, if you got any of those. So now we're going to add in some math and some numbers to what we have been learning. If you have a look at your screen, it should say, an equation, moment equals force times perpendicular distance. And the numbers underneath are called the units. That's what we measure things in. So for example, force is measured in Newtons. If you look at the word force underneath it has a capital N in it, and that means that it is measured in Newtons. If you look at perpendicular distance, because it's a distance, underneath it says M which is metres and CM, which is centimetres. So distance is measured in metres or centimetres. And under moment it says capital N little m or capital Ncm. And the way we say that is Newton metres or Newton centimetres. Okay? So let's do an example question that might come up using this equation. So it says, calculate the moment or turning force of a spanner that is 20 centimetres long when a force of 13 Newtons is applied. So I'm going to draw this out for you. So my force is 13 Newtons. My perpendicular distance is 20 centimetres. That's the information I've got. So the first thing I always always do is write out my equation, moment equals force times perpendicular distance. Then I'm going to put in my numbers. So under force, I'm going to write what my force is. And that was 13 Newtons. Under perpendicular distance, I'm going to write down what my perpendicular distance was, and that was 20 centimetres. So then my moment, I'm just going to put that in my calculator and I get 260 Newton centimetres. And the reason I choose Newton centimetres is because my distance was given to me in centimetres. Here's another example that we're going to do together. So let's read it, calculate the turning force of a wheelbarrow with an arm that is two metres long, when a force of 30 Newtons is applied. First thing I want you to do please, is write out the equation. I've written it there for you, moment equals force times perpendicular distance. So pause the video now and write your equation out. Okay? And now what we're going to do is, underneath force, we're going to write down what the size of the force that they've given us is, and underneath perpendicular distance, we're going to write out what the distance is. So pause again and have a go on your own. So we should have 30 times 2. So my force was 30 Newtons and my distance was 2 metres. And now if I put that in my calculator, I would get 60, but I'm missing my unit. I need to write down either Newton metres or Newton centimetres. I'm going to use Newton metres. And the reason for that is that my distance was given to me in metres. If you have a look, it says two metres. So that means that I need to use Newton metres. Now what I'd like you to do is try these two questions completely on your own. It's the same equation, I've written the equation down for you. So please pause the video now, and have and have a go. Hopefully you've had a go and you found them okay. The answers are 600 Newton centimetres and 300 Newton metres. So I've multiplied force by my perpendicular distance. And then I've chosen either Newton centimetres, or Newton metres by looking at the distance that they've given me. So let's have a quick check. What are the units for moment? Five seconds. They are Newton metres and Newton centimetres. So really well done, if you got that right. What are the units for perpendicular distance? Five seconds. They are centimetres and metres. So really well done, if you got that one right. And what is the unit for force? Five seconds. It is Newtons, option four. So amazing job if you've got all of them right. So sometimes levers are called force multipliers. So this man exerts a force of 100 Newtons on the lever. If the lever is one metres long, the moment will be 100 Newton metres. If the lever is two metres long, the moment will be 200 Newton metres. So if it was one metres long, it would be 100 Newton metres. If it was two metres long, the moment would be 200 Newton metres. Even though the force is the same, the moment is different. So force is the same, but moment has changed. So the force has been multiplied. And because of that, we call levers, force multipliers. So pause the video now and see if you can answer this question. The correct answer is option two. They can increase the moment by changing the perpendicular distance. So if we go back to all those minutes ago, when we learned about closing doors at different places, and we noticed that if we try to push towards the edge of the door, that was much easier than if we were pushing right next to the hinge. And hopefully now you realise that that's because when I'm further away from the hinge or the pivot, my perpendicular distance is bigger. So that means that my moment will be bigger. So it's easier to push. Thank you so much for staying with me to the end of this lesson. I really hope you enjoyed it and that you learned a lot. What you can do now is go on to the exit quiz to show just how much you've learned. If you'd like to please ask your parent or carer to share your work on Instagram, Facebook, or Twitter, tagging @OakNational and #LearnwithOak. I really hope I see you again next lesson.

Worksheet: Levers and pivots

Exit Quiz: Levers and pivots

Completed: Levers and pivots

This lesson introduces what levers and pivots are. It also introduces calculating moments and how to increase the moment of a force.

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Levers and pivots

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