Kinetic Energy K. E. = ½ mv2 Units: J, joules Kinetic energy stored in an object that is moving equals the amount of work done accelerating it from stationary to that speed. Work done = force x displacement But F = ma, and displacement = s So Work done = mas Remember v2 = u2 + 2as Reorganise v2 - u2 = 2as But if the object is stationary at the start, u=0, so, v2 = 2 as This makes = as But W = m . as So W = m . Or Work done = Ek = Gravitational Potential Energy Ep = P. E. = mgh Units: J, Joules Potential Energy is the energy stored in objects which have been lifted against a gravitational field (or you can also have potential energy in magnetic or electric fields - see later). The work done lifting them = potential energy stored in them Work done = Force x displacement Here the force = weight = m x g And the diplacement = height = h So Work done = m x g x h = P. E. gained Note: this equation only applies if g remains constant. This is true for any movement near the Earth's surface.