[Someone]

> if you lift an object to some height, and then you repeat that action (lifting it from there to twice the height), you've done twice the work, and doing twice the work requires twice the caloric intake.

You’re introducing two new intuitions, and it’s not intuitively obvious how they are related to each other. Why would work correlate 100% with caloric intake, and caloric intake 100% with kinetic energy?

Certainly, ‘work’ is highly counterintuitive. If I move a concrete block over loose sand on a beach, I’m doing zero work, in the physics definition, so moving it over a kilometer should be as easy as moving it for a millimeter.

Even ignoring the difference between caloric intake and caloric expenditure, it also isn’t intuitive to me that caloric expenditure is independent of the speed at which one lifts an object.

In the end, the answer is “because the math works out that way, and kinetic energy is a useful concept”

[GroksBarnacles]

Friction. Work isn't just about height.

[thfuran]

Holding that block stationary at arms length then. 0 work.

[dotancohen]

Put that block on a shelf at the same height. 0 work.

The fact that your muscles burn ATP just fighting gravity is a feature of biology, not fundamental to the physics involved.

If you want to read about another similar example, Google for rocket launch gravity losses.

[thfuran]

I think you're missing the point. A lot of basic mechanics actually isn't especially intuitive because things like work simply do not map well to everyday experience. I'm not suggesting that work is defined incorrectly or something.

[dotancohen]

I see what you're saying now, and I agree.