Energy use under different circumstances

[ksoth]

Hello. New here.

Maybe someone can help answer a question that I was having a disagreement with someone over.

I recommended a friend use a StairMaster exercise machine to prepare for a hike. He claimed that StairMasters weren't as good as walking up large numbers of stationary stairs, as in his experience it was much easier to use the StairMaster. My claim was that it was easier because (most likely) he was holding on to the hand rails, and that if he didn't use the hand rails, the work out is (essentially) the same, neglecting minor differences of air resistance.

My friend claimed that because while walking on a StairMaster your elevation is not increasing, you aren't gaining any potential energy, therefor walking on a StairMaster is easier than walking up stairs by that factor. My argument is that you are gaining potential energy because with every step the machine removed potential energy, therefore you have to exert energy to bring you back up, and the net energy expenditure is the same. I used the argument that what if you took the StairMaster to the extreme and used an escalator instead, and if you went up the the top, let the escalator take you down, then go up. He agreed that this would be the same as walking up stairs, but because on a StairMaster the "give and take" of potential energy is happening at the same time, it's not an accurate representation and isn't the same thing.

Then, to try to reinforce the claim, he said replace this case with a motor attached to a cable that is oriented up/down and in such a way that there is no slippage between the motor and the cable. Turn the motor on and let it climb the cable. The motor requires X amount of energy to do this. His claim is that if you pulled the cable down, and turned the motor on such that it stays in the same spot, the motor uses less energy doing this than it does to climb the cable. My claim is that it takes the same amount of energy because in both cases you are doing the same thing: fighting gravity. His claim again is that because in the second scenario the motor isn't gaining any potential energy, it requires less energy to keep it in the same place.

Any thoughts on who is right?

 

[gtoguy97]

Thanks in advance.It sounds like you and your friend have both made valid arguments. It is true that when walking on a StairMaster, one is not gaining any potential energy, which means that it might be easier than walking up stationary stairs. On the other hand, the amount of energy required to keep the motor in the same place is the same as it would take to climb the cable, since the motor is still fighting against gravity either way. Ultimately, it really depends on how much effort one is putting in when using a StairMaster; if they are holding onto the handrails, it will be easier than walking up stairs, but if they are pushing themselves to their physical limits, then it could be just as hard.