Statement of Newton's Laws

Question:   If an object is at rest, how can it start moving?

Answer:      Apply a force.

Question:   What do we need to do to keep a moving object moving?

Answer:      Nothing! If no forces, the speed of an object does not change!

Newton's First Law: For no net force, an object at rest remains at rest, and an object moving at constant velocity continues at constant velocity.

The acceleration a, the rate of change of the velocity, is connected to the total force by:

Newton's Second Law:   ΣF = m a,

where m is the mass of the object. Acceleration equals the total force divided by the mass!

Note: Newton's laws apply in stationary or constant-velocity reference frames---inertial frames. In non-inertial (accelerating) frames, corrections to Newton's Laws arise because of the acceleration.