# What happens if we have a rotating shaft with high RPM but very little torque?

If there are heavy components mounted on it, what will happen? I think it accelerates very slowly, but reaches at the highest RPM at the end because torque is equal to angular acceleration * moment inertia.

Am I correct?

• No different than pushing something very heavy on a ice or wheels with very little force. Mar 20, 2023 at 17:41
• @DKNguyen then case that we have a rotating shaft with high torque but little RPM is similar to it that I'm pushing something heavy on highly-frictional ground with much force? Can we compare it like this based on your analogy? It will reach its maximum RPM very quickly, but maximum RPM is low. Can I say like this? Mar 23, 2023 at 10:59
• Yes. But the point is that in all systems, once you provide enough force or torque to cancel out friction, it behaves like a frictionless system. So any excess torque or force results in acceleration, even if it is very little. Mar 23, 2023 at 13:22
• "because torque is equal to angular acceleration * moment inertia." This is wrong though. The RPM stops increasing when some speed dependent loss equals the torque, or when you simply can't apply the torque fast enough (i.e. you can't turn the crank fast enough even though you still have torque to spare). Mar 23, 2023 at 15:40