Treadmill Physics: Understanding Incline & Work Done

[TimR]

Ok, I think I've confused myself. :-S

How can the incline of a treadmill have any affect on the work done? Surely as there is no actual change in height, there is no change in potential energy and so no significant amount of extra work is done. Why then do treadmills even allow you to change the incline and why have I found equations that involve the supposed change in height? Do you see why i am confused?

Thanks

-Tim

 

[brewnog]

An excellent question! It's easy to see where the confusion arises.

When you're on a treadmill, you are changing your height. Every step you take forwards, you essentially also take upwards, depending on the elevation of the treadmill. The fact that you're (quickly) returned to where you started is irrelevant. This means that a steeper setting will indeed be more difficult, and explains why a gravitational potential term is included in your energy equations.

If, instead of running, you were cycling on the treadmill (and actually could stay in the same place) then the above would not apply.

Let us know if you don't understand, my explanations have been a bit off lately!

Ooh, and also, welcome.

 

[russ_watters]

If, instead of running, you were cycling on the treadmill (and actually could stay in the same place) then the above would not apply.

No, consider what the situation would be like if the treadmill were stopped: the bike would roll down backwards. It takes a force on the pedals to keep the bike stationary in a stopped treadmill, and therefore extra energy when it is moving.

Likewise with the running - you can stay exactly in the same place and still use more energy: since the treadmill is falling away from you, you have to push harder to stay in the same place.

 

[krab]

How can the incline of a treadmill have any affect on the work done?

Or consider the extreme case where the treadmill is vertical. Then it's like a ladder, which as you climb, is lowered so you stay in the same place. You definitely have to apply a force of your own weight, and with arms and legs moving while applying this force, you definitely do work. Where does this energy appear? It is in the brake mechanism that allows the ladder to descend while you remain in place. It is similar to treading water while swimming: you stay in place, but definitely do work; that work appears and is dissipated in the water. Similarly, getting back to the treadmill, you will find that there is something, a brake of some kind, that is built into the mechanism that takes up the energy. Instead of a brake, you could hook up a generator and have your work turned into electricity.

 

[brewnog]

No, consider what the situation would be like if the treadmill were stopped: the bike would roll down backwards. It takes a force on the pedals to keep the bike stationary in a stopped treadmill, and therefore extra energy when it is moving.

Russ 1, brewnog 0. Thanks for that.