Is earth an inertial frame of reference
 
Earth rotates around its axis as also revolves around the sun. In both these motion. Centripetal acceleration is present. Therefore, strictly speaking earth or any frame of reference fixed on earth cannot be taken as an inertial fame. However, as we are dealing with speeds  » x 108 ms-1 (speed of light) and speed of earth is only about 3 x 104 m/s, therefore when small time intervals are involved effect of rotation and revolution of earth can be ignored. Furthermore, this speed of earth can be assumed to be constant. Hence earth or any other frame of reference set up on earth can be taken as an approximately inertial fame of reference.
 
On the contrary, a frame of reference which is accelerated or decelerated is a non-inertial frame.
 
Other examples of inertial frames of reference are:
 
(i)         A frame of reference remaining fixed w.r.t. stars.
(ii)        A space ship moving in outer space, without spinning and with its engine cut off.
            Inertial frames of reference are important because:
(iii)       All fundamental laws of Physics have been formulated in respect of inertial frames.
(iv)       The fundamental laws of Physics have the same mathematic form in all the inertial frames of reference.
(v)        The optical experiments performed in an inertial frame in any direction will always yield the same results. This is isotropic property of the inertial frames of reference.
						

							Earth is not an inertial frame.it is non inertial frame..earth is rotating sphere as it is rotating about its own axis..IT HAS A CENTRIPETAL ACCELARATION DUE TO ROTATION..IN adition earth also revolves round the sun in a period of one year in an orbit of radius 1.49into 10to the power 8km..its orbital velocity v=2piR /T=3into10to the power4..thus reference frame attached to earth is an accelarated frame and is non inertial
						

							
in inertial frame of refrence a=o. BUT earth revolves around the sun and also rotate around its own axis so centripetal force acts on earth which keep earth to revolve around sun in a circular path and according to newton 2nd law when force acts on a body acceleration is produced so earth is non-inertial frame of refrence
						

							
if we consider earth and sun earth is inertial reference frame as it revolve around the sun with constant speed and it hold newton first law but if we consider earth in accordance with sun earth revolve as well as rotate about its own axis so in this case centripetal acceleration is produced and newton first law is not applicable and earth is considered as non inertial reference frame.