# What is the formula for Newton's First Law of Motion?

**First law**: The velocity of a body remains constant unless
the body is acted upon by an external force.

So, if *F* is the net force acting on the body and *a*
is the body's acceleration (the rate of change of its velocity)
then the first law says that:

"If *F* = 0 then *a* = 0."

This in fact follows from **Newton's second law**, which
states that *F* = *ma* (where *m* is the body's
mass).