8th Grade Science/Section 2: Newton's Second Law

Newton’s second law is a quantitative description of the changes that a force can produce on the motion of a body. It is one of the most important in all of physics.

It states that the time rate of change of the momentum of a body is equal in both magnitude and direction to the force imposed on it. The formula is as shown: $$F = m \frac{dV}{dt}$$

The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction. A force applied to a body can change the magnitude of the momentum, or its direction, or both. The formula is as shown: $$p = mv$$

For a body whose mass m is constant, it can be written in the form $$F = ma$$, where F (force) and a (acceleration) are both vector quantities. If a body has a net force acting on it, it is accelerated in accordance with the equation. Conversely, if a body is not accelerated, there is no net force acting on it.