Re: Can u explain to me why F = ma and not F = mv?

In the equation F = m a , force is represented as the product of the mass times the mass's acceleration and is, in effect, a definition of that which causes the acceleration of the mass. The product of mass times velocity is better known as momentum, p, most commonly represented by the equation p = m v .

Force is sometimes represented by another equation, F = dp / dt , or force is the rate of change in momentum with respect to time. The two representations of force are equivalent in that the representation F = dp / dt can be changed as follows; Since the momentum, p, is mass times velocity, F = dp / dt = d ( m v ) / dt = m [ dv / dt ] . And since the change in velocity with respect to time, dv/dt, is acceleration, a, then F = dp / dt = m a . Should you try to stop an object accelerating under the influence of a force, where F = m a , you would have to oppose both the force causing the acceleration, F = m a , and provide the force necessary to reduce the mass's velocity to zero, F = p / t , where t is the time within which the mass's velocity is reduced from v to 0. Should you try to stop an object with a constant velocity, not accelerating, you would still have to provide the force necessary to reduce the mass's velocity to zero, F = p / t.

I hope this answer was what you were looking for. For additional information, any high school or college physics textbook will discuss the background for the above. On the net, you might try searching for +newton +laws.