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Since no work is done in circular motion due to no change in kinetic energy (constant speed) and force being 90 degrees from displacement(centripetal force). Does that mean changing an object's velocity requires no energy?

Or is that energy (net force which is required for centripetal force) inputted but not used up and is released back into the system when circular motion ceases?

I am visualizing this question with an object moving at high speed being caught at one end of a rigid massless rod, the rigid rod can rotate freely at the other end. It makes sense for change in velocity to required no energy as the rod can release at anytime which does no work. But something feels wrong.

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  • $\begingroup$ Though KE depends on an object's mass and velocity vector, we consider only the initial magnitude of velocity in circular motion to find out the KE. Because the direction of velocity is changing for a constant force (centripetal force). When the force is constant, there is no change in KE. For no change in energy, the work becomes 0. $\endgroup$ Commented May 2, 2022 at 15:23

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Yes, so to get the body spinning we need to provide the kinetic energy. But, the kinetic energy remains the same throughout and we don't need to supply any energy as long as the system is ideal. We can harness the kinetic energy if needed

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The Energy you are talking of is the kinetic energy of the mass, which is dependent only on the MAGNITUDE of the velocity vector of the mass. As long as the magnitude is a constant, there's no change in the kinetic energy, and hence no work is required to KEEP the mass in uniform circular motion. However if you are making an object at rest perform uniform circular motion, you NEED to provide it with sufficient energy through work done by you to achieve the velocity vector required to perform that motion.

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