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
to lift 300kg 1 meter like it weighs 60kg, you have to move the 60kg part 5 meters.
The energy required to do so is the same as just lifting 300kg 1 meter, but it gets spread out
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.
> Where is the extra energy coming from?
There is no extra energy. It’s called mechanical advantage.
If you exert a lot of force over a short distance, it’s the same energy as exerting a little force over a long distance.
Levers are long on one end and short on the other, so by pulling the long end a long distance, you can exert more force on the short end over a short distance.
Pulleys loop the rope over so that you pull twice the distance for how far you lift. Thus you can lift twice as much.
You’re exerting less force, but over a longer distance.
Energy = force * distance.
A 2:1 lever moves one side twice as far as the other, and with half the force. The product(energy) is the same on both sides.
Energy/work is force times distance.
Pulleys and levers and gears all work by letting you put in less force, but over a longer distance. Basically you are spreading out the work into more manageable pieces, but it is still the same amount of work/energy.
The concept is called mechanical advantage
Energy used multiplied by time taken to apply force.
1 energy x 1 time = 1 force
0.5 energy x 2 time = 1 force
The pulley reduces energy, but multiplies time by increasing the ropes length. Its the same energy used. Just a lower peak overall.
What you’re referring to is called the cantilever effect. It’s basically the first tool ever created.
In nature, everything is about balance. This is where the phrase action = reaction comes into play. If you push against something, the same force pushes back. By introducing a lever, you get a force applied at some distance from a rotationpoint. Again this has to be in balance, so if you use a lever against something, the force you apply at the length of the lever is balanced against the counter force on the arm at the length of that arm that it pressed against.
If you choose the place where you push to be farther away from the rotation point compared to the position where the counter force is applied, you increase the force. Think of this as you look at a see-saw. When you move farther back from the center, the force of gravity can easier move you down.
When placed correctly (assume equal size and weight distribution) the pulleys split the overall load amongst them. When you apply 50lbs of force to the unweighted side, 50lbs is applied to all pullies and total forced is added ( some pulley configurations have better input/output ratios). The more pulleys you have the more force output with same initial input.
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