﻿Hi, it's Mr Saville again, here with lesson five of your Key Stage 4 topic of forces in motion for science. Today we're going to be looking at work done. But before we are started, please make sure you've found yourself a quite space away from distractions. Today, we are going to be looking at work done. So in particular we are going to be describing, what work done is, we're going to recall the equation for work done, we are also going to have go at calculating work done and we are going to finish like always with an exit quiz. Now, the only equipment you need today is a pen, paper and a calculator. If you need to go and grab those, pause the video now and play when you are ready to start the learning. Okay, so today before we start with work done, and the new content, what I would like you to do is have a go at recalling some of the concepts that we've been through earlier in this topic. And in particular, weight, mass and gravity. So, as a warm up, I'd like you to have a go at questions on the screen. Try and remember the equation. If you can remember the equation, pause the video now and start the questions. If you can't remember the equations, if you think back it was weight equals mass times gravity. Weight measured in newtons, mass in kilogrammes and gravitation field strength in newtons per kilogramme. So, pause the video and have a go at these questions. So, we going to have a check up your warm up answers. And in particular what I want to do is remind you of the way in which you should structure any equation based question. Remember, when your get your question you should always highlight or select the values. So, in this case the values in this question were 82.5 kilogrammes and 9.8 newtons per kilogramme. The second thing you should always do is write your equation down. Now in the exam, you may be given the equation, but you may also be expected to recall this equation. Which is weight equals mass times gravity. The next thing you then need to do is remember substitute in the information you know. So 82 and a half kilogrammes is your mass, 9.8 newtons per kilogramme is gravitational field strength. Do we need to rearrange? No we don't. So now, we just simply input the information into our calculator and get an answer of 808.5. But the the answer of the question should I say asks us to answer it in three significant figures. So we will round it up to 809. And remember with any question in physics, there may be an extra mark for your units. Never forget your units and the units for weight is newtons. So, here is the answer to question two. If you need more time to check this, pause the video now. Here is your answer to question three. So this one was a little different compared to those two. So we're asking how many 'g's did he experience? And I gave you a little hint here by saying that you need to calculate the g and then compare to it's normal gravitational field strength of 9.8 newtons per kilogramme. So, once you've got your answer of 29.4, hopefully you got that. What you then need to do is divide that by earth's gravitational field strength 9.8. So this person when they were launching into spaceX dragon caspule they will experience three times the amount of g gravitational field strength of earth. So, today we are going to talk about work done. Before we start talking about it, what I would like you to do is pause the video and copy down the information on the screen now. So, as I said, we're going to talk about work done today. Now when a force causes an object to move through a distance, work is done on that object. Now to put it as simple as I can, work is a measure of the energy transferred when a force moves an object. So, for work to be happening, the object has to be moving. And this would be because of a resultant force. Now we can talk about lots of examples in real life scenarios. So, for example, when I go shopping, I get my troller and I push the troller, I will be exacting a force on my troller thus I will be doing work on my troller 'cause I am transferring the energy to that troller. Now, we always talk about energy transfers. If you think about back to previous topics in science, we can talk about energy transfers. And whenever energy is transferred mechanically to an object so for example, kinetic energy or gravitational, the object will be transferring energy. And it's important to remember that when an object physically moves, work is usually done against friction. And if you remember back to the first lesson, friction is when two objects are opposing each others motion. Friction will always transfer energy to a thermal store of that object. Meaning that the temperature will increase. And lastly, remember what I said, if the object doesn't move, then no work can be done. No energy will be transferred to that object. Now, in your exam you may be required to recall the equation that links work done, force and distance. Now before we talk about this, what I'd like you to again is pause the video, make sure that you've written this equation down. So now you've got this equation down, it's important that we remember it. So you can see here, that work done is equal to force times distance. Now if you remember what I told you, work was a measure of energy transfer when a force exerts itself on an object moving a particular distance. This will help you remember the equation. And the symbols are on the screen for you as well. So, we've got capital W equals capital F times s. Now, you might be asking yourself why is s distance. Well, in fact what we are actually talking about is not distance, we're talking about displacement. But for your exams you just need to recognise that the equation will be work done equals force times distance. It's also important to remember your units. Now, we know the units of forces, newtons. We also know the units for distance, metres. But, we don't know the units of work done yet. But, if you remember what I've just said, work done is a measure of energy transferred when a force makes an object move a certain distance. So, we are talking about energy. And energy is always measured in joules. So, the units for work done are joules. And you can also express work done in the units newton metres and one Joule is equal to one newton metre. So, watch out for that trick question in an exam where you will work out the work done for example 100 joules, it will then for an extra mile ask you to convert it to newton metres when in fact it will be the exact same answer with newton metres rather than joules. So, we going to do a quick check of what we've learnt so far. So, again all I want you to do, you've done this before, or you just shout the answers out. I'm only going to give you three seconds on each slide. So, the first one, what are the units for work done? So, three, two, one, I can hear you all shouting joules, okay. Excellent, well done. Next question. What object or what does an object need to do for work to be done? So three, two, one. An object needs to move. Excellent if you got that already. Next question. Recall the correct equation for work done. Give you a chance to have a look here. We're going to put the answer up in three, two, one, W equal F times s. Excellent if you remembered that one. Next question. What happens to an object when work is done against a frictional force? Three, two, one. Temperature of the object will increase, it will rise. So, we're going to have a go at calculating work done now. And what I would like you to do first is put your pens down and just make sure you are watching how I do it myself. We'll then do a couple together, I'll then set you on a task to calculate some yourself. Now, we have a question here on work done. So a car engine exerts a resultant force of 3100 newtons to move a car 25 metres. Calculate the work done. Now, think back to the start of the lesson when we did the warm up part activity. In previous lesson when we had equations. I want you to follow the same structure every single time. So, the first thing that we do, and what I'm going to do now is that I'm going to highlight or identify my values. 25 metres, 3100 newtons. Next thing I'm going to do is decide which equation I am to use. Well, the question say that I calculate the work done. So, I know it's going to be W equals F times s. Work done equals force times distance. The next thing I need to do is then substitute in the information I know. Well, I don't know the work cause that's what its asking me to calculate, but I do know the force and I do know the distance, so I'm going to put those in. Now, next thing do I need to rearrange? Well, in this case I don't, so I'm going to leave this blank which then brings me to my answer which again I can simply input into the calculator to get answer of 77500 and as in all questions in physics remember your units and remember and as said now, units for work done remember can be transferred it is joules. So, we're going to have a go doing one together now. To start us off, what I would like you to do is to take a second to read the question. So, this question says, a bike exerts a resultant force of 6000 newton to move the bike 50 metres. Calculate the work done. Now, we're going to do this one together. Remember, the structure of our calculations. First thing that we are going to do is highlight the values we know. So, think to yourself, now what are the values we know? So, we know we've got 6000 newtons and we've got 50 metres. Next thing I want you to do is have a think of which equation we will be using. Can you remember it? So it's asking us to work out work done. Which means the equation must be work done equals force times distance. The next thing we will do together now is substitute in the values that we know. So, we know that force is 6000 and we know the distance is 50 metres. Do we have to do any rearranging? No we don't. So we're going to leave that one blank. Which then leaves you to answer the question. Input that into calculator, hopefully you got the same answer as me. I'm going to show that in three, two, one. So 300,000. And remember those all important units. Work done is similar to energy transferred and the unit will be joules. Excellent work if you got that without my help. We're going to have another go at doing one together before I put you into an independent task. So, again have a read of the question. So a climber and all his gear weighs 750 newtons. Calculate the energy transferred climbing onto the top of the 20 metres cliff. Now before we start this question, this is something that is relevant to a lot of the exam questions you get on the work done. Now, we know the work done is force times distance. And it's clear here that we have a distance of 20 metres. But do we have a force? Lots of student get confused when we talk about the weight of an object. Remember, that weight is a force. So, whenever we talk about about weight we can assume that is the force we are going to be using in the question. So first of all, do we know values? Yes we know. 750 newtons, we also know 20 metres. The equation as I've just said is work done equals force times distance. We know the distance is 20 metres. The grey area here is what the force is. What it says is the persons weight and all his gear is 750 newtons. That is the force. So here do we need to do any substitutions? We don't. So all we're left to do now is answer the question. Input that into your calculator, you should get an answer of 15000 joules. Excellent work if you got that again without any of my help. So we're going to have a go at practising some of these ourselves now. So in a second when I tell you that I would like you to pause the video and have go at these questions. But before you do that, let me remind you that work done is force times distance. Let me also remind you that you have to read questions in detail. A lot of questions may ask you to answer in significant figures, you may have to convert some units, and if you don't do this you will loose easy marks. So please look out for that when you are answering these questions. When you finish the questions after you pause the video, you can play the video again and you can check those answers. So if you'd like to pause the video now. So, hopefully you've done that, and you managed to remember the equations to start of with and you calculated these answers correctly, displayed them correctly and put the correct units. So, lets have a check on these answers. So, the answers are on the screen now. What you can do is pause the video if you need more time to check them. I am really confident that you've got all this correct. The one I would just like to talk about is the one at the bottom, question four. So here we got a man transfers 0.45 kilojoules of energy to move a load 13 metres. Now we know that kilojoules needs converting into joules. And to do that you would times it by 1000. So we've actually got 450 joules and if we read the question actually what we're trying to work out this time is force, not work done. So, as you write down the structure of your answer, once you go to the rearrange section, hopefully you realise that you have to rearrange the equation and it was work 450 divided by the distance of 13 to give you the answer 34.615. That wasn't done right 'cause it also asked you to answer it in 3 significant figures which would lead you to 34.7. Amazing job if you got four out of four on those. We're going to have a go at multi-step equations now. And this is a skill that you may have to do in an exam that could be worth up to four to six marks. So it's important that you are confident in using multi-step equations. Now, I'm going to show you how to one of these before I let you do one yourself. So, I'm going to read this question to you. A person lifts a bar up from the floor and raises it two metres. The bar has a mass of 10 kilogrammes. Calculate the work done. Now, I know that we going to have to use two equations for this. As a tip, what I would say to you is always think about your end equation. What equation can I use to calculate work done? Now, I can hear you shouting at the screen, it's what we've been doing today. The equation is work done equals force times distance. Now, with any structure equation, once we've got the equation itself, what I would like you to do is to substitute in the information we know. Do we know the work done? We don't. Do we know the force? Reading the question actually doesn't give us any force. Do we know the distance? We know the distance. So, I'm going to put that in there, two metres. Now what we need to do is think of an equation that will give us force. Once we've got force we can then answer the question, calculate work done. So I need to think of an equation that has force in it. I also need to think of an equation that has some of the information above in the question. So anything that has the distance two metres or has mass in it. Now if you think back to the warm up part we said or think back to our previous lesson, there is an equation that has mass in it and force. And in terms of force I mean weight. And I can hear you shouting out loud it's weight equals mass times gravity. Now, if I use this equation first, I can calculate weight. And remember, weight is a force. So what I'm going to do from here is substitute in the information I know. So weight equals 10 because we've got 10 kilogrammes of mass and we're going to times by the gravitational field strength of air which is 9.8 newtons per kilogramme. If we do that we will get an answer of 98 newtons. Now this bar has a weight of 98 newtons. So, for this person to lift this bar up, he's going to need to use a force of 98 newtons. That will be our force. So from here, what we can then to do is further substitute in the information into our end equation, that work done equals force times distance. We know the distance is two. Now we know that the force is 98. So what we're simply going to do is 98 times two which will give us the work done as 196 newtons. Now if you can do that, you could possibly pick up a lot of marks in an exam like I said four to six marks. I have seen it before in an exam. So, what I would like you to do and this is a challenge question, I would like you have a go at completing one of this types of questions yourself. Think about the structure I've just done, think about your end equation and then think about what first equation can you do use to get some more information for your end equation. If you want to have a go at it now, you can pause the video and we're going to check answers once you are ready by pressing play. So, as I said this was a challenge question. So, anyone who's doing this or even attempted it, amazing job. What we're going to do is now is we're going to check this answer. So, first thing we're going to do is the weight equals mass times gravity equation. That is for us to be able to get the force for our final equation of work done equals to force times distance. Now, to calculate weight, you know from the start of the lesson and from previous lessons that we're going to do 59 times 9.8 which will give us the weight as 539 newtons. Now that is our force. Do we know the distance? Yes we do. So the distance here is 5.3. So what we're going to do from here is 539 newtons of force times 5.3 metres of distance to give us an answer of work done as 2856.7 joules. And as I said, this was a real challenge question. So if you got that correct, give yourself a massive pat on the back. So what we're going to do now is we're going to have a look at applying your knowledge to some exam questions. Here is your first exam question. If you'd like to pause the video have a go at the question and when you are ready press play to reveal the answer. Question 2, again, what I would like you to do, is this is a two part question, three marks in total. What I would like you to do is pause the video, have a go at the question and play the video again to reveal the answer. Lastly, exam question for today. So this is worth two marks again. What I would like you to do is pause the video, ensure you read the whole question, have a go and when you are ready to reveal the answer press play again. Before we finish today, what I'd like to do is to quickly recap the learning. So, remember, work done is a measure of energy transferred when a force moves an object a certain distance. Remember, the unit for work done is joules that can be converted into newton metres and one joule is equal to one newton metre. Remember, with work done, the object has to be moving for energy to be transferred. Now if an object isn't moving then the work done would be zero. Remember, the equation for work done 'cause you may have to remember it in an exam. Work done is equals to the force times distance. What I would like you to do now is complete your exit quiz and worksheet that has lots of additional calculations for work done. Now that brings us to the end of today's lesson. As always, I want to give you a really big well done on the fantastic learning you've achieved today. I've got two final things I would like you to do. So first of all as ever, I'd like you to look back on today's learning and write down the three most important things you have learnt today. Second one, if you would like to, what I would like you to do is ask your parent or carer to share your work on Instagram, Facebook or Twitter and tag @OakNational and #LearnwithOak. We would like to see all the amazing learning you've done today. That's all from me and what I'll do is I'll see you in the next lesson of Key Stage 4 Forces and Motion

In this lesson we define work done, introduce the equation for work done and use it to calculate force and distance.

Combined Science

Y11 Combined Science (Foundation)

Key Stage 4

Year 11

Forces and work

Forces (FT)

UNIT

Forces: An introduction

Weight, mass and gravity

Resultant forces

Forces and elasticity (Part 1)

Forces and elasticity (Part 2)

Speed

Distance: Time graphs

Acceleration

Velocity: Time Graphs

Terminal velocity

Newton's Laws

Acceleration RPA (Part 1)

Acceleration RPA (Part 2)

Stopping distance

Combined science review

Case Study: Sir Isaac Newton

Y11 Combined Science (Higher)

Forces (HT)

Resolving forces (HT)

Momentum

Physics

Y11 Physics

Forces

Moments and levers

Moments and gears

Pressure

Pressure in fluids

Atmospheric pressure

Collisions and car safety

Physics only review

Lesson overview: Forces and work

Video

Presentation

Worksheet

Exit Quiz

Transcript

17 lessons in Forces (FT):

18 lessons in Forces (HT):

25 lessons in Forces: