In an inertial reference frame,
-sailor(Ocean & Mountain);
2018-10-21{255}(#11756093@0)
the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma. (It is assumed here that the mass m is constant – see below.)
https://en.wikipedia.org/wiki/Newton's_laws_of_motion
The second law states that the rate of change of momentum of a body is directly proportional to the force applied, and this change in momentum takes place in the direction of the applied force.
-111111(快乐老家);
2018-10-21{134}(#11756170@0)
What is difference between them? Which one is original definition ? Why are there two different definitions OR statements ? Thank you.
What you said is an implication of F=ma.
-sailor(Ocean & Mountain);
2018-10-21(#11756176@0)
You are right. However, the Momentum is the Key.
-111111(快乐老家);
2018-10-21(#11756255@0)