Newton’s Laws of Motion

Sir Isaac Newton studied the behaviour of bodies in motion and was able to come up with three laws governing motion and they are as follows:

Newton’s First Law of Motion:

A body will continue to be in a state of rest or of uniform motion unless it is acted upon by an external force.

Newton’s Second Law of Motion:

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

Therefore, \( \scriptsize F \propto \normalsize \frac{change \: in \: momentum}{time} \)

\( \scriptsize F \propto \normalsize \frac{mv \: - \: mu}{t} \)

\( \scriptsize F \propto \normalsize \frac{m(v \: - \: u)}{t} \)

Recall that a = \(\frac{final \: velocity\: - \: initial \: velocity}{time} \)

a = \(\frac{v\: - \:u}{t} \), from equation of motion

\( \scriptsize F \propto ma \)

Introducing a constant, k, = 1

F = kma, k = 1

F = ma

The unit of force is Newton, and it is a vector quantityVector quantities are quantities with magnitude and direction. Examples of vector quantities include displacement, velocity, position, force, and torque. More.

Newton is a force which gives us a mass of 1kg on acceleration of 1ms^-2 . 

From second law

F = \( \frac{mv\; - \;mu}{t} \)

Ft = mv – mu.

Recall that Ft = Impulse of a force

Impulse of a force = the change in momentum of the body.

Example 9.2.1:

A body of