Does using a lever require less energy?

[Baby Astronaut]

If machine A were to lift 1000 kilos directly, and machine B were to use a lever for better advantage in lifting the same 1000 kilos, would machine B spend less energy?

 

The machine can be a robot, and the lever is some tool it found laying around.

[Klaynos]

Ask yourself these questions...

 

What is the energy required to lift a 1000kg mass 1m in the air?

 

Does this energy depend on anything other than mass, height and gravity?

[Baby Astronaut]

I didn't mean less energy total -- just from one doing the lifting. If each robot had a full battery, would they have equal levels remaining in their batteries if one used a lever and the other didn't?

[Klaynos]

It would depend on the motor design in the robots...

 

Fundamentally all you can compare is the total energy... Just adding a leaver taking nothing else into account you could say there will be friction at the pivot of the leaver so that will infact take more energy than without a leaver...

[Mokele]

From a purely physical standpoint, the energy input and output (as well as the power) must be the same, otherwise the lever would create or destroy energy.

 

From a biological standpoint, a lever system that minimizes displacement and velocity will require less metabolic energy, because the efficiency of converting metabolic energy to mechanical energy goes down the faster and greater magnitude the muscle contraction.

[swansont]

I didn't mean less energy total -- just from one doing the lifting. If each robot had a full battery, would they have equal levels remaining in their batteries if one used a lever and the other didn't?

 

The one doing the lifting is providing all the energy. You are doing work, and trading a larger displacement for a smaller force, because there can be a limit on how much force you can exert.

[Baby Astronaut]

From a purely physical standpoint, the energy input and output (as well as the power) must be the same, otherwise the lever would create or destroy energy.

 

From a biological standpoint, a lever system that minimizes displacement and velocity will require less metabolic energy, because the efficiency of converting metabolic energy to mechanical energy goes down the faster and greater magnitude the muscle contraction.

I didn't entirely grasp you're saying. But I'm only concerned with energy input. If I were to lift the side of a car with my bare hands, and the next day I were to lift it again using a jack with a crank, I'd burn less calories that next day.

[Mokele]

Correct, but only due to the properties of muscles. A robot would notice no such difference.

[Cap'n Refsmmat]

The amount of work would be the same in either case, as work is force times distance -- a decrease in force would require a corresponding increase in distance. (You'd have to push the lever farther if it's easier to push.)

[D H]

The amount of work would be the same in either case, as work is force times distance

That's a bit too simplistic. As Klaynos already noted, this ignores works against friction, parasitic losses inside the engine, etc. Mechanical advantage typically comes at a cost of increased energy expenditures. Those non-conservative forces are a real drag.

[Klaynos]

Correct, but only due to the properties of muscles. A robot would notice no such difference.

 

Only if the robot is ideal, I suspect just like human muscle act differently in the two situations so would the robots 'motors' but without more information it's impossible to say which loose the most energy.

[Sisyphus]

Ok, getting ahead of ourselves. In an ideal model, the energy used is exactly the same in both cases, because the same work is done. This has to be the case, otherwise energy would be created or destroyed, which never happens. The way a lever works is by allowing you to use less force over a longer distance, which adds up to the same amount of work done. (You pull the end of the jack handle up and down many times, and the jack slowly creeps upwards.) Thus you can accomplish tasks that would otherwise require more force than you can exert, but not more energy than you have available. (Like, for example, lifting a car.)

 

While this is all true, in the non-ideal case (i.e., reality), it's a bit more complicated, which is what other people are talking about. No machine is perfect, so generally the more complicated you make it the more energy is lost. (Well, not lost. It becomes heat or noise or something similar, the point being it's not doing useful work.) So you'll probably end up using slightly more energy overall, but it'll still be easier because you're using less force. And as Mokele points out, muscles are very complicated and imperfect machines as well. They have different efficiency levels at different degrees of exertion. Straining yourself is much less efficient (more energy converted to non-useful forms) than exerting moderate force over a longer period. So you will burn less calories using a lever, because less of those calories become heat (or whatever, that stuff is foggy to me).

[Baby Astronaut]

Thus you can accomplish tasks that would otherwise require more force than you can exert, but not more energy than you have available. (Like, for example, lifting a car.)

OK, I see.

 

Identical amounts of energy don't always produce the same amount of force. Plus, energy use isn't the same as energy input. Therefore the number of calories a person burns doesn't matter -- a lot of those calories won't have made it in.