<P> In the given interpretation mass, acceleration, momentum, and (most importantly) force are assumed to be externally defined quantities . This is the most common, but not the only interpretation of the way one can consider the laws to be a definition of these quantities . </P> <P> Newtonian mechanics has been superseded by special relativity, but it is still useful as an approximation when the speeds involved are much slower than the speed of light . </P> <P> The first law states that if the net force (the vector sum of all forces acting on an object) is zero, then the velocity of the object is constant . Velocity is a vector quantity which expresses both the object's speed and the direction of its motion; therefore, the statement that the object's velocity is constant is a statement that both its speed and the direction of its motion are constant . </P> <P> The first law can be stated mathematically when the mass is a non-zero constant, as, </P>

What does the first law of motion state