It is a riddle.

It is the strongest force,

to resist your force,

and yet it is not a force.

It never accelerates,

but it is always moving.

It never rests, and

it never gets tired.

It has been defined many ways,

but no one can quite capture it.

What is it?

The first definition that Amon gives from the dictionary, the process of acceleration. Acceleration is computed in Mathematics by the use of last and first velocities. As there are last and first velocities, it implies the change of velocities instead of the constant velocities.

The second definition that Amon gives from the dictionary is the change of velocity. As there is a change of velocity, the last and first velocities are different.

Now look at the spinning of the earth. The spinning of the earth around the sun is constant and that can never be any change of velocity. As there is no change of velocity, the acceleration would turn up to be zero so to say by using the Mathematics formula. Thus, acceleration in general term cannot be used to discuss the spining of the earth around the sun. If you do not believe please use the formula to compute acceleration if the velocity is zero. You must know that the last velocity is the same as the first velocity and after substracting them, it is zero acceleration.

Thanks.