FORCE AND MOTION

Forces are pushes or pulls that change the motion of objects. To make a stationary object move, or a moving object stop, a force is needed. A force is also required to change the speed or direction of an object. This change in speed or direction is known as acceleration. Acceleration depends on the size (magnitude) of the force and on the mass of the object. The effects of forces were first summarized by Isaac Newton in his three laws of motion. the international unit of force, named after him, is known as newton (N), which is approximately equal to the weight of one apple. Gravity-the force attraction between any two masses can be measured using newton meter (spring balance). Forces are put to useful effect in machines. A simple machine, such as a wheel and axle, is a device that changes the size or direction of an applied force. It allows an applied force (the effort) to produce another force (the load). A lever uses a bar that turns on a fulcrum to exert force. In all simple machines, there is a relationship between force and distance. A small force (in a compound pulley, for instance) moves through a large distance to lift a heavy object a small distance. This is called the Law of simple Machines.