merrypark3 said:
The concept of proper force in relativity refers to the force experienced by an object due to its own motion in spacetime. It is also known as the intrinsic force or the 4-force. It takes into account both the spatial and temporal components of an object's motion.
Proper force is closely related to the concept of proper time in relativity. Proper time is the time measured by an observer who is at rest relative to the object, while proper force is the force measured by an observer who is at rest relative to the object. Both proper time and proper force take into account the effects of time dilation and length contraction due to the object's motion.
In classical mechanics, force is considered a conserved quantity. However, in relativity, proper force is not a conserved quantity. This is because energy and momentum, which are conserved in relativity, are related to proper force through the 4-force, but not directly dependent on it.
Apparent force, also known as fictitious force, is a force that appears to act on an object due to its motion in a non-inertial frame of reference. On the other hand, proper force is the force experienced by an object due to its own motion in spacetime. While apparent force is a result of the frame of reference, proper force is an intrinsic property of the object itself.
Proper force cannot be measured directly because it is a theoretical concept that takes into account the effects of relativity on an object's motion. However, it can be indirectly measured by observing the effects of proper force on an object's energy and momentum, which can be measured directly.