Mills for producing flour from grains were very early users of machines. Trace the use of machines to turn millstones from the earliest recorded time to the present. Create a bulletin board display illustrating the three classes of levers. Use both posters diagramming each type, and pictures or drawings of machines, appliances, and devices that use each type. Physicists define work as being done when a force is exerted and the object on which the force is exerted moves.
Work continues to be done as long as the force is still being exerted on the object.
When you throw a ball, you are doing work on the ball while your arm is moving forward. Once you release the ball, you are no longer doing work on the ball. If you push as hard as you can on a wall, and the wall doesn't move, you aren't doing any work on the wall. Physicists calculate the amount of work done by multiplying the force applied by the distance in metres over which the force is exerted. Force is measured in units of newtons.