In physics, force is a quantitative description of an interaction that causes a change in an object’s motion. Force is a vector quantity, with both direction and magnitude. It is defined as Mass x Acceleration = Force. The SI unit of force is the newton (N); defined as the unit of force which would give to a mass of one kilogram an acceleration of 1 meter per second squared. There are a lot of force types including tension, compression, shearing, bending, and friction.
Newton’s Universal Law of Gravitation states that any two objects exert a gravitational force of attraction on each other. The gravitational acceleration of earth is defined as g＝9.80665m/s2 (standard value) by International Committee of Weights and Measures. For example, the weight of 1kg mass at earth is nearly equal to 1(kg)×9.8(m/s2)＝9.8(N).