Forces and reactions
The application of a force on a body will cause the body to accelerate. Similarly, if a body of mass m tends to be accelerated but is restrained from doing so, then the restraining force will be given by:
P = ma Now all objects in the proximity of the Earth tend to be accelerated
towards the centre of the Earth's mass due to gravitational attraction. At mean sea-level this acceleration, i.e. the acceleration due to gravity, has a magnitude of 9·81 m/ s2. Hence all objects resting on the surface of the Earth are held down or 'weighed down' by a force (often referred to as the weight of the object) which has a magnitude of 9·81 times the mass of the object.