Question

Why can work output be less than work Input but never be more?

Answer 1

This is very steep...I'll try:

Explanation:

First we have a conceptual problem:
If you have a look at Energy and Work (=energy in motion) in particular you'll see that it has to come from somewhere. I mean, you cannot create energy from nothing. This means that if you input, say, `10J` of energy it is impossible to build an engine to "create" (from nothing) energy to get out `11J`. The surplus energy has to come from somewhere.

Now imagine again you can build an engine that produces more output work than input work: you could use the extra output (in our example `1J`) and feed the rest (`10J`) back into your engine and basically build a system that is self-sustaining or that is continuously producing work without external intervention!

This has never been built and although you cannot demonstrate (mathematically) its impossibility it goes against all the laws of Physics (and of logic if you think about it!).

This idea is embedded into the Second Law of Thermodynamics and is the conceptual foundation of the idea of Entropy.
In Physics we simplify an engine as a system that takes energy (in form of heat, for example) and gives out Work (mechanical) and energy (heat).
I would suggest you to have a look at this second law and in particular at the Carnot Cycle and the idea of Entropy.

I am not sure I answered your question in satisfactory manner but...

Answer 2

It is illogical to expect more. See analogy below.

Explanation:

You have a task of baking bread for a large family gathering. You go to the only store in the small town near your gathering and ask for 20 kg of flour. The clerk says "Sorry, I have only 2 of the 5 kg bags".
You say "I don't care how much you have. You sell flour. Give me 20 kg."
"But I have only 10 kg!"

Stupid story. It is simply illogical to suggest the clerk can give you more than he has.

Once you understand energy (unit: Joules) and work (unit: Joules) better, you will understand that your question is equally illogical. The clerk can not create additional flour for you out of nothing and the system you need to do work for you can not create additional work for you from nothing.

I hope this helps,
Steve