- #1
lamina
- 10
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Over Unity Efficient Pulley?
Hi, I have a problem regarding a simple pulley system which seems to have an efficiency of over 100% and I just can't figure out what is going on.
Scenario:
I have a 5N mass vertically suspended using high tensile flexible steel wire from a simple spring gauge which measures force. The force measured is 5N. As expected.
I now place the steel wire over a plastic pulley with solid steel supports - and measure the force shown on the spring gauge to lift the 5N mass - this is shown as 4.5N. If I carefully lift the pulley so that it is not touching the wire, the force shown on the spring gauge goes back up to 5N.
If I replace the pulley with a polished solid steel bar, the force is always above 5N - frictional effects I suppose.
So I am lifting a 5N mass with a force of 4.5N - efficiency 111%
Assuming that I am not being REALLY daft ( always a possibility) where has the 0.5N come from?
I have tried smaller masses, different wires and just about anything I can think of.
This is driving me nuts and any help would be appreciated.
I would add that I have tried more than a single pulley system and have acheived efficiencies approaching 200%.
Regards
Richard
Hi, I have a problem regarding a simple pulley system which seems to have an efficiency of over 100% and I just can't figure out what is going on.
Scenario:
I have a 5N mass vertically suspended using high tensile flexible steel wire from a simple spring gauge which measures force. The force measured is 5N. As expected.
I now place the steel wire over a plastic pulley with solid steel supports - and measure the force shown on the spring gauge to lift the 5N mass - this is shown as 4.5N. If I carefully lift the pulley so that it is not touching the wire, the force shown on the spring gauge goes back up to 5N.
If I replace the pulley with a polished solid steel bar, the force is always above 5N - frictional effects I suppose.
So I am lifting a 5N mass with a force of 4.5N - efficiency 111%
Assuming that I am not being REALLY daft ( always a possibility) where has the 0.5N come from?
I have tried smaller masses, different wires and just about anything I can think of.
This is driving me nuts and any help would be appreciated.
I would add that I have tried more than a single pulley system and have acheived efficiencies approaching 200%.
Regards
Richard