The kinetic energy of a moving object is given by half × mass × speed squared, or Ek = ½ m v2, with mass in kg, speed in m/s and energy in J. A 2 kg trolley moving at 3 m/s has ½ × 2 × 32 = 9 J. Because speed is squared, doubling the speed makes the kinetic energy four times bigger.
An object raised above the ground gains gravitational potential energy: Ep = m g h, with mass in kg, gravitational field strength g in N/kg and height in m. On Earth, g = 10 N/kg. Lifting a 3 kg object through 2 m gives 3 × 10 × 2 = 60 J. If it then falls and we ignore air resistance, this energy is transferred to its kinetic store.
A stretched spring stores elastic potential energy. The energy transferred in stretching is half × spring constant × extension squared, or E = ½ k x2, with k in N/m and the extension x in m. These equations can be tested with light gates and trolleys for kinetic energy, or by using a motor to lift a weight for potential energy.