Q. Why Newton's Second Law is called the real law of motion?
Ans: Newton's Second law of motion is called real law of motion because all the laws can be derived and are contained in this law.
Proof:
We know, F = m. a,
Where f is the external force applied on a body, ‘m’ is the mass, and ‘a’ is the acceleration produced due to external force.
If no external force acts on a body, then F = 0, since f = ma, a = 0 because mass of a body cannot be 0.
This means an object at rest will always be at rest and object moving with uniform motion in a straight line will continue to do so, which is the first law.
To prove that third law is also contained in the second law of motion, we take two bodies A and B moving along the same straight line. As a result of a collision, their momentum will change. Let t be the time of impact, then change in linear momentum of A is
PA = FA x t
Similarly, change in momentum of B is
PB = FB x t
So, the total change in momentum of A and B is,
P = pA + pB
= FA x t + FB x t
If no force acts then, P = 0
Or, FA x t + FB x t = 0
Or, FA x t = - FB x t
Or FA = -FB, which is newton’s third law of motion.
Share on Social Media