Where is the extra energy coming from?
If I can lift a maximum of 60kg with my bare hands, but then I can lift 300kg using pulleys/levers, where did that extra energy come from? Will I still burn calories like I am lifting 60kg or 300kg?
In: Physics
There is no extra energy. They increase force BECAUSE the energy needs to be conserved.
Energy = force × distance. (distance here is the distance the end of the lever arm moves)
To make something move, you need to spend a set amount of energy.
With a small lever, you’re using a lot of force over a short distance. So, say, 500 N of force × 0.1 m distance = 50 J of energy.
With a lever that’s twice the size of that first one, you’re using half the force over twice a longer distance. So, 250 N of force × 0.2 m distance = 50 J.
So, by getting a longer lever, you decreased the required force you need to move it, but you increased the distance by which you need to move it, so the total energy expenditure remained the same for both levers.
That’s what mechanical advantage mechanisms do (pulleys, levers, gears, etc.). You trade force for distance. Or torque for speed in case of rotating shafts.
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