Here’s kind of what I’m thinking: A strong man carries an object weighing 100kg 15 meters from the living room to the shed. It takes him a couple of minutes. A distance runner carries a backpack weighing 5kg 10,000 meters from one town to the next and it takes him 45 minutes. Which task is harder?
Where I’m stuck is, if Work is Force X Distance, and if it takes no force to keep an object moving at a steady rate, then was any “work” done (ignoring the initial lifting of the object)? Because clearly tremendous effort was required for either task, but I don’t know how to measure “effort” because it’s not exactly “work”.
In: 0
Keeping an object moving with 0 work requires a system with 0 friction. There obviously is friction in the real world, so there is work being done to move both objects horizontally. If you could assume 0 friction, you would need neither your strongman nor your distance runner, because you could just slide the packages along your icy ground.
You can determine the amount of energy used by taking your power (wattage) over the duration * the duration.
So a bike rider riding at 100 Watts for 30 minutes uses the same amount of energy as a rider at 200 Watts for 15 minutes.
The piece you’re missing is that the biomechanics of the human body make calculating “energy spent” far more complicated than simply multiplying force times distance.
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There’s two big issues. First, you’re trying to neatly map a word that describes the human experience to a physics definition. That doesn’t really happen. Even work has to be split into different definitions. I got a lot of work done this morning at work. Did I apply a large force over a long distance? No, I made a lot of good progress on the tasks I’m doing. You’re not going to be do that really well.
You’re also looking at a stupidly simplified problem, you’re in spherical cow and frictionless vacuum land. Humans are stupidly complex electro-chemo-mechanical systems. Here’s a simpler example. Is it easier to lift a heavy weight a short distance, or a light weight a long distance. Same energy right? Well, how are you lifting them? Can the light weight one even lift the heavy one, or will it collapse? Does it need structural reinforcement? Can I use the same motor? What’s the efficiency difference? Do I need hydraulics or gearing. I don’t know, it depends. Do you see how it’s not a simple question
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