Question

Which law of Newton defines the inertial Frame of Reference?
A) First law of motion
B) Second law of motion
C) Third law of motion
D) Law of Gravitation

Answer 1

Hint: There are three laws of motion proposed by Newton. They correspond to the inertia of a body, force acting on or by the body and mutual forces. Law of gravitation is also an important theorem by Newton describing the relation of gravitational force between two bodies, but it is not a part of the three laws of motion.

Complete step by step answer:
What is inertia? Well, inertia is a property of any object by virtue of which it resists any change in its motion, whether it is in rest or in uniform motion.

Inertial frame of reference simply means a frame in which a body stays in continuous motion or rest.

Newton’s First Law of Motion states that, “Every body continues in its state of rest or in uniform motion in a straight line unless it is compelled to change that state by forces impressed upon it.”

This means that a body does not break its inertia until acted on by an unbalanced external force. To illustrate this by an example, when we travel in a bus at a certain velocity, we are then experiencing inertia of uniform motion or simply, motion. But when brakes are applied suddenly, we move forward, conserving that inertia of motion.

Thus the correct answer is (A), First law of motion.

Additional Information:
The statement for Newton’s second law is that acceleration of a body is inversely proportional to its mass and directly proportional to the resultant external force acting on it.
That is, $F_{net}=ma$ where $F_{net}$ is the resultant external force, $m$ is the mass of the body and $a$ is its acceleration.
The statement for newton’s third law is, forces always occur in pairs. If a body A exerts a force on body B, then an equal but opposite force is exerted by body B upon body A.

Note: Theoretical question. First law supports an inertial frame of reference, second law is the definition of force itself and third law demonstrates the nature of force. If we are asked which law describes the definition of force, the answer will be the second law of motion and if we are asked which law defines equal and opposite nature of force, the answer will be the third law of motion. Law of gravitation describes the force of attraction between two objects.