Second Law of Motion is the real law of Motion Physics Notes

Second Law of Motion is the real law of Motion:
(A) First law is contained in the second law:
According to Newton’s second law of motion, the force acting on a body is given by:

Thus there is no force is applied on the body then the body at rest will remains at rest and a body in uniform motion will continue to move uniformly along the same straight path. Hence first law of motion is contained in the second law.

(B) Third law is contained in the second law: consider an isolated system of two bodies A and B suppose the two bodies interact mutually with one another, Let \(\vec{F}_{B A}\) be the force (action) exerted by A or B.

Let \(\frac{d \overrightarrow{p_{B}}}{d t}\) be the resulting charge of momentum of B.

Let \(\vec{F}_{B A}\) be the force (reaction) exerted by B or A Let \(\frac{d \overrightarrow{p_{A}}}{d t}\) be the resulting change of momentom of A

According to Newtons IInd law of motion:
Second Law of Motion is the real law of Motion Physics Notes 2
in the absence of external force, the rate of change in momentum must be zero.
\(\overrightarrow{F_{B A}}+\overrightarrow{F_{A B}}\) =0 ⇒ \(\vec{F}_{B A}=-\vec{F}_{A B}\)
This indicate Newton’s IIIrd law of motion we can say that Newton’s IIIrd law is the real law of motion.