Force and Laws of Motion

A book resting on a table, A person standing still, Two people pulling a rope with equal force in opposite directions

Balanced forces occur when forces acting on an object are equal in magnitude but opposite in direction, resulting in no change in motion. A book on a table has balanced gravitational and normal forces, a standing person has balanced forces, and equal pulling forces balance each other out.

For every action, there is an equal and opposite reaction, Action and reaction forces are equal in magnitude, Action and reaction forces act simultaneously

Newton's third law states that action and reaction forces are equal in magnitude, opposite in direction, and act simultaneously on different objects. They don't cancel each other because they act on different objects.

Mass and velocity

Momentum (p) is defined as the product of mass (m) and velocity (v), so p = mv. It is a vector quantity with the same direction as velocity.

kg⋅m⋅s⁻¹

The SI unit of momentum is kg⋅m⋅s⁻¹ (kilogram-meter per second), derived from p = mv where mass is in kg and velocity is in m/s. Note that N⋅s is also equivalent to this unit.