Question

explain why Newton's second law of motion is called real law of motion

Answer 1

Hey mate, here is your answer. hope it helps.

Newton's second law is called the real law because the 1st and 3rd law of motion can be derived by using this law.

Answer 2

Newton's second law of motion is called the real law of motion because the first and the third law can be proved using it.

• 'The second law states that the force applied on a particle is directly proportional to the rate of change of momentum.'

Proving the first law:

• "A particle in the state of rest or motion will continue to be in that state until a net external force is applied to it."

• Using the second law we can infer that if there is no external force on a particle,  the rate of change of momentum will also be zero.
• Since the mass of the body remains constant, to keep momentum$(mass*velocity)$ constant, the velocity must remain constant.
• This proves the first law that no external force implies no change in the state of motion.

Proving the third law:

• "For every action, there exists an equal and opposite reaction"
• If two bodies A and B are interacting in such a way that A is exerting $F_{BA}$ on B and B is exerting $F_{AB}$ on A.
• Since there is no external force,

                             $(\frac{dp}{dt})_{net} =0$

                       ⇒  $(\frac{dp}{dt}) _A+(\frac{dp}{dt})_B =0$

                       ⇒ $(\frac{dp}{dt})_A =-(\frac{dp}{dt})_B$

                       ⇒ $F_{BA}=-F_{AB}$

• Hence, Newton's second law of motion is called the real law of motion.