[Scott Johnston]

Asi;

I’m no physicist either.  As an engineer, I have to dumb things down from the Fizziks level to the Engineer (people who drive trains) level.

This is fun and has caused me to spend some time on the interwebs.  It turns out this is a subject (climbing a down escalator) that has a fair bit of discussion surrounding it.  Let me start by saying: “You are correct” and I have been wrong all these years.  Touche, and thank you! I love learning things.

I stumbled upon a Reddit post where a group of engineers were debating this very thing.  Those engineers, like me, didn’t come to the same conclusion that you did by using the “frame of reference” argument.   They and I came to it from the kinetic vs. potential energy argument.

Climbing fixed stairs involves increasing the potential energy of the person by the amount of kinetic energy it takes to move the mass vertically some distance.

In my now discarded model, I only considered that the person on the stair machine was not increasing their potential energy by moving farther from the surface of the earth. Thus the chemical energy needed to do the work of climbing the down escalator was less than climbing stairs.

What helped me see the error in my thinking is that the escalator climber stays stationary by doing work on the machine to make the stairs move.  That work, instead of being converted into the potential energy of raising his mass, is instead converted into heat by the friction of the machine.

Using a thermodynamics (energy) viewpoint is what finally made the dim bulb in my brain flicker to life.

Thanks,
Scott