It has been said that no work is done on a box moving at a constant speed on a conveyor after the box comes to rest relative to the conveyor. Yet, companies transferring box loads of products on conveyors incur energy costs for moving the boxes. Does this mean that the energy costs incurred by the companies in moving the boxes come primarily from the initial phase of the box motion before they come to rest? Does it mean the movement of the boxes incur no cost (i.e. consume no energy) beyond the point they come to rest on the conveyor?
2 Answers
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A part of the energy costs are spent on accelerating boxes just dropped on the conveyer belt from rest to the speed of the conveyer belt. This process of acceleration is actually quite wasteful, as there is heat generated due to slipping of the box when its speed is not yet equal to the speed of the conveyer belt. There will also be energy losses in the gear system of the conveyer, motor etc.
Total power loss $(P)=\frac{\Delta KE}{\Delta t}+$friction between block and conveyer$+$other losses
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Once the box is moving at a constant speed in a straight line then a horizontal conveyor belt does no further work on the box. But the conveyor belt will still consume energy due to internal friction.
And, of course, production lines are not all horizontal straight lines ...
answered Jun 22, 2021 at 4:18