Accelerating, the earth is a non-inertial reference frame.How close is the earth to being an inertial r.f.?

Answer 1

True at low speeds the affects from the accelerations are nelgiable. But don't try to launch an intercontinetal ballistc missile without taking them into account...you might blow up the wrong soccor field.

To answer your question: Its pretty far off from being one since the earth is both rotating around its axis and orbiting around the sun. However, one can modify newtons laws by translating to a rotating coordinate system and introducing fictitious forces (such as the centrifugal force and the Coriolis force) to account for the accelerations.

Answer 2

Love the pendulum example, very beautiful to watch as well. Look into the Lagrange points, they may give you some ideas, don't forget there are 5, for the Earth Moon Sun system. Since the sun is swinging around the galactic arm, not much hope of having a true intertial Ref, just have to go with a relative reference point.

Answer 3

If you conduct experiments of motion over short times and short distances, it is a good approximation to inertial because the earth rotates so slowly. Try doing an equation of motion especially involving a pendulum over hours and you'll get bad answers