Work is done whenever a force acts over a distance, e. g. a car motor produces a forward force to move the car a certain distance. Energy is measured in Joules, J. The work done or energy transferred can be calculated using: Work done or energy = force x distance When working out the work done the force must be in the same direction as the movement. If more than one force is acting in that direction then the resultant force must be used. Kinetic energy is the amount of movement energy an object has. Kinetic energy can be calculated using: kinetic energy = ½ x mass x velocity2 Gravitational potential energy is the extra amount of stored energy an object has because it is higher up. GPE can be calculated using: Change in gravitational potential energy = mass x gravity x change in height This is the same thing as GPE = weight x height Power is the rate at which work is done, or in other words, the amount of energy transferred per second. Power is measured in Watts, W or J/s. Power can be calculated using: power = energy transferred / time taken or power = work done / time taken Energy is often lost to the surroundings as heat energy. This is wasted energy as it cannot be easily used again. Efficiency tells us how much energy is wasted when an energy transfer has happened. The more efficient something is the less energy that is wasted. Efficiency can be calculated using: