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d3uk61
12-09-2009, 03:39 AM
Asking this question is a bit embarassing but I need to get this clear:

If a crane lifts a weight and the crane is standing on a giant force plate then the GRF measured by the force plate will increase as the weight accelerates to a certain terminal velocity. Once this velocity is reached and the weight displaces vertically at a constant velocity, what will be the total weight / force measured by the force plate. Lets say the weight is 200kg and the crane weight = 2000kg = total 2200kg and the acceleration of the weight is 2m/s/s and terminal velocity is 4m/s.

There appears to be no acceleration of the weight after the initial acceleration but since gravity is acting on it there must be a force acting opposite to gravity to keep it moving vertically therefore there must be an acceleration that increases the total force and yet there is a constant velocity which implies no force increase. Which is it?

I was trying to answer a question asked to me about the nature and reason for flat spots in the peaks of force time curve as characterised by a force plate software. I found an intuitive block to my answer i.e. the maths don't seem to agree with intuitive concept.

Cheers Dave Smith