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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
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