Question

what inertial frame of reference ? Is the earth an inertial frame ? If not , why ?​

Answer 1

Answer:

Earth is assumed as an inertial frame of reference.

Explanation:

Consider a block placed on a lift, being weighed by a spring balance. When the lift is at rest, for an observer standing inside the lift, block is at rest. However, if the block starts moving vertically downwards/upwards, for an observer standing outside the lift lift and the block inside it are moving ( coming downward/upward ) :

Now, when block is moving :

• For the observer inside the lift : Weight of the block is opposed by the tension in spring which mean W = T, where W is the weight of block and T is the tension in spring.
• For the observer outside the lift : Weight of the block is greater than the tension in spring which say W ≠ T { W - T = ma( acceleration in body ) }

For these purposes there are two fram of references :

1. Inertial frame of reference
2. Non-inertial frame of reference

In inertial frame of reference, acceleration of the observer is either 0 or uniform with respect to the object.

Since earth keeps on moving, earth is not an inertial frame, however a( ≈ 0.034 m/s^2 ) in W - T = ma is too small that it can be ignored. Thus, we treat earth as a inertial frame of reference.

Answer 2

Earth is indeed an inertial frame for all local events that occur on Earth. But Earth is not an inertial frame from cosmic point of view. Because it's moving in an elliptical orbit which means its direction is

changing every moment implying constant change of velocity.