Force
Force is a push or pull that can change the state of motion or shape of an object. It is a vector. SI unit is the newton (N).
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What is force?
Force is that which can change the state of rest or of uniform motion of a body, or change its shape. It is a vector: it has magnitude and direction. The SI unit of force is the newton (N): 1 N is the force that gives a mass of 1 kg an acceleration of 1 m/s². So F = ma.
Types of forces
Forces can be contact forces (e.g. friction, normal force, tension) or non-contact forces (e.g. gravitational force, magnetic force, electrostatic force). Forces occur in pairs: when body A exerts a force on body B, B exerts an equal and opposite force on A (Newton's third law).
Effect of force
A net (unbalanced) force causes acceleration. If the net force on an object is zero, the object remains at rest or moves with constant velocity (Newton's first law). Force is central to the study of mechanics and Newton's laws of motion.
When you stand on the ground, the ground pushes up on you. What is the pair to this force, and why don't they cancel?