Work, it is used to determine how much of it is done on an object, for example we look at this picture we see that the person is pulling the object, which is an example of doing work on an object. Let's look at a real life example, you're in a grocery store pushing a shopping cart, you are doing work on the shopping cart by applying a force on it. However there are 2 different types of work and both can impact the object, the first one is positive work and it is when the force applied is going in the same direction as the displacement. We look back at the shopping cart example and see that the force applied is going forwards which is the same as the displacement of the shopping cart which is going forward. Negative work is when the force is going in the opposite direction of the displacement. For example you're sledding down a hill, the force of kinetic friction is slowing your sled down so its diagonally upwards, while the displacement is diagonally downwards. There are examples of when there is no work done on an object, for example you're holding a box, now this box is being held, however the box is not moving so displacement is 0 and there is no force applied to it so the force is 0 indicating that the box is at rest and there is no work done on the box.