Someone asked me this question today and I admit I don't know the answer. There are some pretty good minds in RCM. Maybe one of you can enlighten me.
When something is in motion, like a motor with a flywheel or a vehicle on a straight and level road, and the power is cut off, does the speed decrease linearly or logarithmically? If we graphed the decrease in speed would it be a straight line or a parabolic curve, steepening as the speed reaches zero?
This is a question of inertia versus friction. If the speed decreases linearly, friction is constant while inertia bleeds off at a constant rate. If the speed decreases logarithmically, the ratio of friction to inertia is increasing as the speed reaches zero.
I have a 2-HP pedestal grinder in my shop. When I shut the motor off, it takes about three minutes for the wheels to come to a dead stop. This suggests linear decrease to me, although that could be an illusion.
What is the correct answer?
-Frank