Its pretty obvious when we're exerting force, but how do we know if we're doing work? Work is done when an object is moved some distance, in the direction that the force was applied. It is defined by the force exerted multiplied by the displacement of the object. We can examine some examples of work by watching someone lifting weights in the gym. He starts by lifting the weight, until it is above his head. He has done work on the bar, because he exerted force up, and the bar moved up. Now he starts to lower the bar, however he still must exert force upwards to make sure the bar doesn’t fall too fast. This time he is not doing work, because he is exerting force up, but the bar is moving down.
1. Charles and George are each moving identical blocks from point A to point B. George pushes the block directly from point A to point B, whereas Charles pushes the block to the right, and then curves back to point B. Who does more work?
2. A shopper is holding a box while he travels up an elevator. He must exert an upwards force while he’s holding the box, to counteract the force of gravity. Is he doing work on the box as the elevator moves from the first floor to the second floor?
3. A strongman pushes against a large rock with all his might, but is unable to the move the rock. Is he doing work?