Question

Is the earth a inertial frame of reference or not, if yes why?​

Answer 1

Answer:

inertial frame of reference means frame of reference has no acceleration and on which Newton law of motion is applicable perfectly

when a body moves in circle there is always centripetal force that makes body to move in circle and that centripetal force is responsible for the centripetal acceleration .as we know earth moves around sun in elliptical path(as ellipse is the general case of circular),to move around the sun ,earth always have centripetal acceleration. so ,earth is not an inertial frame of reference.

Answer 2

The surface of the Earth is not, rigorously speaking, an inertial frame of reference. Objects at rest relative to Earth's surface are actually subject to a series of inertial effects, like the ficticious forces (Coriolis, centrifugal etc.) because of Earth's rotation, precession and other kinds of acceleration.

When solving physics problems, however, we usually take the Earth frame as being inertial. This is because the inertial effects are minuscule for most of our day-to-day experiences and experiments. For example, objects in the Equator are the ones subject to the strongest centrifugal force and it is only about 3×10−33×10−3 or 0.3%0.3% of their weight.

So for the most part, if an experiment is short enough and happens in a small enough region, the surface of Earth can indeed be approximated to an inertial frame of reference since the effects on the experiment's results are very, very tiny.

This of course has exceptions, as cited in njspeer's answer.

If however by "Earth" you mean the reference frame in Earth's center, it is an inertial frame according to General Relativity (GR), since observers in free fall are inertial in GR. The Earth actually does have some proper acceleration due to external forces such as radiation pressure, but these are also minuscule effects.