Weight is the force acting on an object due to gravity. The force of gravity close to the Earth is due to the gravitational field around the Earth. • The weight of an object depends on the gravitational field strength at the point where the object is. • The weight of an object can be calculated using the equation: weight = mass × gravitational field strength, W = m g. weight, W, in newtons, N; mass, m, in kilograms, kg; gravitational field strength, g, in newtons per kilogram, N/kg (In any calculation the value of the gravitational field strength (g) will be given.) • The weight of an object may be considered to act at a single point referred to as the object’s ‘centre of mass’. • The weight of an object and the mass of an object are directly proportional. • Weight is measured using a calibrated spring-balance (a newtonmeter).