Question

A reference frame attached to the earth when viewer is in the space:
A. Is an inertial frame by definition
B. Cannot be an inertial frame because the earth is revolving around the sun
C. Is an inertial frame because Newton’s laws are applicable in this frame
D. Cannot be inertial frame because the earth is rotating about its axis

Answer 1

Hint: In an inertial frame, Newton’s laws of motion are valid. For the frame to be inertial, the frame of reference should not be acted upon by the external force and acceleration of the body should be zero.

Complete step by step answer:
To answer this question we need to understand what is an inertial frame and non-inertial frame of reference.

Inertial frame of reference: We know that in an inertial frame of reference, Newton’s laws of motion are held true. The body in an inertial frame has zero acceleration and no external force acts on it.

Non-inertial frame of reference: We know that in a non-inertial frame of reference, Newton’s laws of motion are not applicable as the body does not have constant velocity. External forces act on the body to cause change in direction and velocity of the body.

We know that Earth does not retain constant velocity while revolving around the sun. It has greater velocity in its orbit when the earth is close to the sun and less velocity as it is farthest from the sun. Therefore, we can see the acceleration of the earth is non-zero. Also, we know that the revolution of the earth around the sun is due to centripetal force acting on the earth. The reference frame cannot be inertial if it is acted upon by an external force. Thus, the option (B) holds true.

Newton’s laws are applicable for this frame of reference for the observer standing on the earth. For the observer in space, the frame attached to the earth is still non-inertial. Therefore, the option (C) is incorrect.

While earth moves rotate around itself, the centripetal force acts on the reference frame attached to the earth. Therefore, we can see for the observer in space, the reference frame attached to the earth is not the inertial frame. Therefore, the option (D) holds true.

Therefore, the correct answer is options (B) and (D).

Note:
Note that for the observer on the surface of earth, the reference frame attached to the earth is an inertial frame as the observer and reference frame are in the same state of motion. To answer such types of questions regarding inertial frame and non-inertial frame, the key is to remember the conditions which should be followed by the reference frame.