So notice that the forceĪnd the displacement are in the opposite direction. So, what direction is theįorce of gravity acting? Well, gravity alwaysĪcts downwards, right? So the force of gravity is downward, but the ball is moving up. Again, pause the videoĪnd think about this. We're throwing the ball up, just concentrate on the Work, or negative work? Again, have a look at it one more time. The work done by gravity during the upward motion of the ball? Do you think it's positive Now during this time, gravity is putting aįorce on that ball, right? So can you think about Let's say we throw it up, and consider the upward Imagine we take a ball and we throw it up. On that ball is to the left, and the ball moved to the right, so the force and displacementĪre in the opposite direction, which means while catching that ball, you did negative work on that ball. Towards the left, isn't it? That's what you're doing, but in what direction is the ball moving? Both the ball and your handĪre moving back, right? They are moving backĪs you stop that ball. Now, in what direction are you pushing? Look at where your hand is placed, you're pushing that ball So as the ball comes towards you, the moment you make contact with the ball you start pushing that ball. Can you think about this, whether the work done by you on that ball, is it a positive work or a negative work? Go ahead, pause the videoĪnd think about this. In that case, you areĭoing work on that ball, because you are puttingĪ force on that ball and the ball is moving. Imagine you play catch,Īnd a ball is thrown, and you catch that ball. It's mostly because work done in physics can mean very different things compared to work done Yet Superman, who saved the day, did negative, less than zero work, which means Superman, strictly speaking, did less work than these people. They did absolutely nothing, so they did zero work. Who might be just standing and watching this show, Now here's where it sounds a little weird, if you look at some people The car is to the right, but it's being displaced to the left, so the force and displacementĪre in the opposite direction. Okay? But what direction is that car moving? Well, the car is moving to the left. Pushing on this car? Well from here you can kind of see, he's trying to slow down that car, he's pushing on it towards the right. The moment Superman starts pushing on it, to try and stop it, he puts a force on it. Let's see if this is positive or negative. Now let's think about the workĭone by Superman on the car. On the other hand, imagineĪn uncontrollable car that is being stopped by Superman. So here the force and the displacement are in the same direction, and therefore here she's doing That cart is moving, it is moving in the same direction, to the right, itself. If we look at the direction of the force, she's pushing it to the right. Now, is that work positive or negative? Well, let's see. Then she is doing work on it because she is pushing itĪnd she is making it move. Pushing on a grocery cart and makes it move. On the other hand, if theįorce and the displacement happen to be in the opposite direction, and we'll look at some examples, then we'll say work done is negative, this is when work doneīecomes smaller than zero because a negative number Now, if the force and displacement happen to be in the same direction, that's when we say work done is positive, it's a positive number. To do that, let's make some space, so let me write this in short form, let me just write it as W equals F into s. Out when it's positive and when it's negative. This work done can be both positive and negative. This means that to do work, in physics, you need to push or pull on something, and while pushing or pulling, It's calculated as forceĭisplacement of that object. The least you can do, right? But in physics, you can do even less work. If you just lie around doing nothing, you do zero work, that's In our normal day-to-day life, the minimum amount of work
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