Laws of Motion

The idea that an external force

The idea that an external force is needed to keep a body in motion is incorrect. In practice, a moving body slows down because friction or other resis

A body remains at rest

A body remains at rest or in uniform straight-line motion unless acted upon by an external force. In simple form, if the net external force is zero, a

Momentum is defined by p =

Momentum is defined by p = mv and is a vector quantity. It depends on both mass and velocity, so heavier or faster bodies have greater momentum.

The rate of change of momentum

The rate of change of momentum is proportional to the applied force and acts in the direction of the force. In SI units, F = dp/dt = ma. The law is ve

Impulse = force × time duration

Impulse = force × time duration = change in momentum. It is important when a large force acts for a very short time, such as in a catch or collision.