Understanding Force

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                Newton's Second Law Of Motion


Force Lessons

Newton's First Law of Motion
Newton's Second Law of Motion
Newton's Third Law of Motion
Weight and Mass
Calculating Force




Newton's second law of motion states as follows:

The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction in which the force acts.

Before continuing, let's see what momentum is

The momentum of a body is defined as the product of its mass and its velocity.

That is, the momentum of a body is equal to mv. With mass in kg and velocity in m/s, the Standard International (SI) unit of momentum is kgm/s.

Notice that the greater the momentum of a body, the greater the force it will exert on another body.

Now back to Newton's second law of motion:

Mathematically, Newton's second law of motion can be expressed as

Force α change in momentum/time

 F α (mv-mu)/t 

where F represents a force on a body of mass m causing it to change its velocity from u (initial velocity) to v (final velocity) over a time t.

Simplifying further, we have

F α m(v-u)/t

 (v-u)/t is the rate of change of velocity, and is same as acceleration, a.

Therefore,                   F α ma,  and

F = kma, where k is the force constant. The SI unit of force is the Newton (N).

It is the force which acts on a body of 1kg, making it to accelerate by 1m/s2.

Therefore, when F is in Newtons, m in kg and a in m/s2,

                              F = ma

                                Or F = m(v-u)/t


See calculations of force based on Newton's second law of motion here.
See Newton's Third Law Of Motion