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