Vocabulary Words relative motion ~ change in position of one object compared to the position of some fixed object frame of reference ~ objects that don't seem to move define your fram of reference speed ~ the rate at which an object's position changes velocity ~ the speed and the direction an object is moving force ~ any push or pull friction ~ force that acts when two surfaces rub together gravity ~ an attractive force between two or more objects over a distance. The more mass an boject has, the stronger the gravitational force. work ~ using force in order to move an object a certain distance kinetic energy ~ energy of motion potential energy ~ the amount of energy available to do work because of the way a system is arranged lever ~ a simple machine made of a bar resting on a fulcrum fulcrum ~ the support on which a lever plus its load rests load ~ the weight that is to be lifted or moved effort ~ the force used on a simple machine wheel and axle ~ a simple machine made of a wheel and a rod joined to the center of the wheel pulley ~ a simple machine made of a wheel with a rope around it. inclined plane ~ a simple machine like a ramp wedge ~ a simple machine that is made of two inclined planes put together and that can be driven into another material screw ~ a simple machine made of a stick with ridges wrapped around it |