Question

My understanding is that without acceleration the movement of a body is a relative concept, i.e. we can choose an inertial frame of reference where the body is at rest and there is no property or experiment that can tell us that the body is in movement, because it's a meaningless question.

In the same way, can I say that the movement of earth is arbitrary, just choosing a non-inertial frame of reference? The fact that I need to include fictitious forces to explain for example the movement of a Foucault pendulum, means that the earth rotation is absolute? The law of physics should stay the same if I choose the earth as frame of reference, but does that mean that there is nothing absolute about the movement of the earth?

Answer 1

Earth's movement can be considered relative to the chosen frame of reference, but fictitious forces in a non-inertial frame indicate acceleration that differentiates it from an inertial frame. Newton's laws apply simplest in inertial frames, where all forces have physical origins.

Step-by-step explanation:

The movement of a body, including the Earth's rotation, can indeed be considered relative and is described based on the choice of a frame of reference. The use of non-inertial frames of reference is legitimate and often useful, for instance, when analyzing the movement of a Foucault pendulum or examining the effects experienced by passengers in a car. However, the need to include fictitious forces, such as centrifugal force or the Coriolis force, in a non-inertial frame, like a rotating Earth, indicates that the motion is not the same as it would be observed from an inertial frame of reference, which does not accelerate or rotate relative to known inertial frames. These fictitious forces do not have an identifiable physical origin but arise due to the acceleration or rotation of the frame itself.

In an inertial frame of reference, all forces involved have a real physical origin, and Newton's laws of motion apply in their simplest forms. When viewed from such a frame, the motion of the Earth can be said to be absolute to the extent that it involves real forces causing acceleration, like gravity. The crucial factor in determining the 'absoluteness' of the Earth's movement, or any object for that matter, is whether the frame of reference used to describe it is accelerating or rotating. While the laws of physics are consistent across all frames of reference, the recognition of inertial forces reveals the non-inertial nature of a frame like one tied to the Earth's rotation.