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nhluhr wrote:Arbitrarily changing a frame of reference does not allow you to ignore the change in potential energy... which I specified above. This is the simplest of physics: PE gained = weight * height gained. If you don't go UP you're not doing that work to store PE.

Yes, you still have resistance and yes it is pretty close to actual, but it's NOT EQUAL and the difference in work output can be offset if you just use the stepmill at a faster rate but on a per-step basis, each step of a stepmill is less work performed than an actual step, not that it matters for the guy who started the thread, because he has actual flights of stairs to climb.

No.

What do you think potential energy is? It's due to gravity. Why don't you go ahead and draw a free body diagram, indicating all the forces acting on the human in both cases and compare. Relative to the stairs, in both cases, the person is moving up against gravity.

Calorie counters? You mean those crappy websites. Who knows what their estimates are based on.

Oh, given your stance you must also believe that running on an incline on the treadmill and running outside are drastically different (well they are different in the surface under the feet). However there is research showing the similarity between the two.

I'm not saying these things are identical, but they differ at more specific levels, not the general 'potential energy' level.

Ze wrote:

nhluhr wrote:Arbitrarily changing a frame of reference does not allow you to ignore the change in potential energy... which I specified above. This is the simplest of physics: PE gained = weight * height gained. If you don't go UP you're not doing that work to store PE.

Yes, you still have resistance and yes it is pretty close to actual, but it's NOT EQUAL and the difference in work output can be offset if you just use the stepmill at a faster rate but on a per-step basis, each step of a stepmill is less work performed than an actual step, not that it matters for the guy who started the thread, because he has actual flights of stairs to climb.

No.

What do you think potential energy is? It's due to gravity. Why don't you go ahead and draw a free body diagram, indicating all the forces acting on the human in both cases and compare. Relative to the stairs, in both cases, the person is moving up against gravity.

<slaps forehead> why don't YOU draw the diagram.

Your weight is generated by the earth's gravity, not the steps on the machine. If you don't move through this field relative to its center, your potential energy is not changing. The only work you're doing is the kinetic energy it takes to move the step-mill around and scrub off that movement as heat.

Quite simply, if you don't move relative to the gravitational field, you don't change potential energy. This is a relatively simple definition and it does NOT allow for arbitrary frames of reference other than the gravitational field. I'm sorry you don't get it, but I'm not going to waste my time drawing diagrams for something that is EASILY visualized.

A step-mill is likely to provide a smoother force curve throughout the step but do not be fooled into thinking it is in any way the same as real motion (which, after all, is the end goal here anyway).

nhluhr wrote:<slaps forehead> why don't YOU draw the diagram.

Your weight is generated by the earth's gravity, not the steps on the machine. If you don't move through this field relative to its center, your potential energy is not changing. The only work you're doing is the kinetic energy it takes to move the step-mill around and scrub off that movement as heat.

Quite simply, if you don't move relative to the gravitational field, you don't change potential energy. This is a relatively simple definition and it does NOT allow for arbitrary frames of reference other than the gravitational field. I'm sorry you don't get it, but I'm not going to waste my time drawing diagrams for something that is EASILY visualized.

A step-mill is likely to provide a smoother force curve throughout the step but do not be fooled into thinking it is in any way the same as real motion (which, after all, is the end goal here anyway).

So you think reference frame does not matter. Okay

If you only define the Center of Mass (CM) relative to the ground, then on a stairclimber the velocity of the CM is zero. And the height does not change.

In that case, you would say that the potential energy change is constant, and the kinetic energy (mv^2) is constant and zero.

So according to you, there is no change in energy. A person on a stairclimber is performing no energy moving the center of mass. Do you really believe that?

A sane person would say, hey, what if we account for the velocity of the stairclimber in the equation? Then all of a sudden, the kinetic and potential energies (and changes) make sense.

Gravity is an acceleration. The two reference frames (ground and stairclimber) differ in velocity but do no accelerate relative to one another. Gravity still acts.

Put it another way: The person standing on the stairclimber momentarily at rest moves down negatively, then pushes up and moves up positively from that lower position.

You're all over the place with non-sequiturs, improper terms, and incomplete visualization of the problem

I think I've fallen prey to a troll

So basically you have no response other than ad hominem attacks. I'll take that as "I'm wrong, Zé."

surfnturf wrote:this thread just got good... this is awesome...

Ze wrote:So basically you have no response other than ad hominem attacks. I'll take that as "I'm wrong, Zé."

Wait a minute... aren't you the guy who thinks hyperventilation is the cure for AMS?

Nevermind!

well hey, I guess you don't ready threads very well, a pattern emerging

I thought PE stood for Physical Education.

There isn't any simple physics problem that we can't make more complicated.