ELI5. How do we measure or equate something like “effort” in a task? When is carrying a light object over a longer distance equal to carrying a heavier object over a shorter distance?

Question

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”.

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Answer 1

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.