Much of the confusion in this thread comes from the word “falling”. Like the fact that the moon is ‘falling’ towards the earth. If, while standing still, you ‘fall’ forward you can easily rectify the situation by placing the other foot in front of you. This will not propel you forward - it will only stop your fall.
As Duhkecco pointed out earlier, in a vacuum…
But we are not talking about “fundamental physics”, we are talking about what the OP was asking about, “Is a person running at 5 MPH on a flat treadmill spending the same effort as a person running 5 MPH on the street?”. The answer to that is NO, s/he will spend less.
But ther IS a change of altitude. The alitude change is between where you WOULD be if you stayed still (the escalator takes you down) and where you ARE by moving.
You’re still not moving your mass upwards though (so if fighting gravity is the same as acceleration, then you’re not accelerating). If you were already heading down on the escalator before you started running, then I can see your point, but it would only apply for the first few moments as you stopped heading downhill. Once the mass of your body is stationary with respect to the gravitational body (Earth), surely the only energy you are using is whatever is required to freewheel your legs - yes, those legs are supporting your body, but that body isn’t going anywhere. After you’ve got up to speed, the gravitational/acceleration thing ceases to count. Doesn’t it?
You are using your legs to stop your mass from moving downwards which is the same thing.
Lets look at an extreme example. You are standing halfway up a very long ladder that is capable of moving down at the same rate you can climb up. If the ladder is stationary you don’t need much energy to keep yourself there, same as required to stand on the ground. If the ladder is descending though then you need to move your mass upwards relative to the ladder. It is not simply a matter of your arms and legs “freewheeling” what do you think is stopping your body moving down? It is your arms and legs effectively lifting your body.
By this reasong putting a treadmill on an incline would have no effect. But this isn’t true.
But, since we also know that the physics of the situation says that there is no difference, what we have to look for is the why of the biomechanics. Since it is clear that the biomechanics of a human-powered treadmill match the biomechanics of a regular runner on a road pretty well, (which, by the way, would indicate that the same physics is going on…), the question then becomes why the runner on the powered treadmill runs differently.
I suggest that the answer is touched upon by the person who asked the question of Owen Anderson, Ph.D. in the first link offered by Duhkecco on this subject. Namely, the runner changes his mechanics because of a psychological difference in what he is accomplishing. This causes the runner to “reach” more (notice the fact that the lower leg run through a greater range of motion, being less vertical at impact).
So, in sum, it appears that the answer to the OP is: there is no difference other than wind-resistance for human-powered treadmills. For motorized treadmills, the difference is largely explained by wind-resistance, but there is some biomechanical factor, the reason for which is unknown, but for which physics supplies no ready answer, leading some to believe it is the result of psychological aspects.
We don’t know that. If it were a simple setup it would be easier to say they are the same, but it’s not a simple setup.
One obvious difference is the ratio of the runners mass to the force require to alter the earth’s spin vs the force required to alter the belt’s movement. They are many orders of magnitude different and could be important factors in the equation of the resulting motion.
So here are some questions I have:
When the runner pushes off his/her foot, does the belt provide the same resistive force that the earth provides? Or is the human forceful enough to alter the speed of the belt at that point in time which in turn alters the running style/energy/etc.
When the runner plants his/her forward foot, is the belt able to retain it’s speed in the same way that the earth is able to (any change is not noticeable)?
This is exactly what we need to figure out. And we can’t eliminate the “powered treadmill” as a critical variable.
It could be psychological change in running style that actually results in more efficient running (because studies support the less energy expended notion), but I don’t think anyone has enough information to just come to that conclusion.
I don’t think the data we have seen supports the “no difference” statement even for torque treadmills. Maybe “little difference” but not “no difference”.
Physics can supply the answer, it’s just that nobody has modeled it in enough detail.
One additional thought: It’s possible wind resistance causes the runner to lean forward more which alters the biomechanics of the situation. If true, wind resistance would require more energy to counter than with the treadmill, and at the same time it causes the runner to run less efficiently.
Physics has a ready answer. I have a ready answer. Why is everyone ignoring my posts? !$!@##!
There is no reason to be propelled forward. You only have to maintain your momentum. That momentum is lost in various ways. In a wheel it’s simple, it’s lost at the bearing. When walking, because of the trickier mechanism i described in my previous post, the momentum can be lost in various ways. Three big factors come to mind: your legs aren’t rigid enough to convert momentum into elevation and back, your gait is not symmetric (which messes with some rules of pendulum motion), and energy used to lift your legs is non-recoverable. The extreme regularity, flatness, and monotonicity of the treadmill allows you to be more efficient. To convert momentum into height and then back closer to 100% efficiency than on the more irregular road or on a non-motorized treadmill that doesn’t keep you paced to a perfect rhythm.
The effect of uneven road surfaces and even slight wind resistance is being excessively discounted. OTOH the ability to force yourself to keep a pace on a treadmill is a distinct advantage.
The server just ate my post for some reason, lets try again…
When I run on a treadmill, I make sure I run on an incline because I do find it easier than running the same distance on the road. It also gives you time to ‘switch off’ and get lost in these kind of problems whilst running!
The way I’ve been thinking about it is that when I’m running outside, my body has significant kinetic energy which is partly converted into elastic potential in my muscles as my foot his the floor, and converted again into kinetic as I complete my stride. This energy has come from me and it’s come from when I’ve accelerated from rest, along with the ‘little’ energy I expend keeping at speed.
However, on a treadmill, the energy from the track moving is given to your muscles partly for use in the stride. Although your body works to stop from moving backwards and relatively this is the same as moving forward, your mass plays a significant part. Your mass makes inhibits your rearward acceleration by the treadmill, and the energy of the treadmill is stored somewhat by your legs.
I have noticed, however, when running outside that the effect of momentum helps with keeping up higher speeds and after the intial burst, it’s easier to keep going (especially if the end is in sight). I dont know if I’m only noticing the fact that it’s nicer to run outside, though.
Can you explain why then in a foot race one person “wins” and everyone else is trying their best to. Is the winner simply maintaining momentum better… or could it be that the winner is actually propelling his or herself forward faster?
It’s not the energy of the treadmill that’s being stored - it’s energy from your muscles. Your mass inhibits your rearward acceleration on a treadmill, but that’s exactly the same thing as your mass keeping you in motion on a road.
On a hypothetical treadmill of size large enough that you can stay on it (including standing still) for long enough to make detailed observations, of sufficiently decent engineering that it doesn’t significantly vibrate or change speed, without visual or tactile reference to outside objects - there is nothing you could do to tell the difference between:
-The treadmill is stopped and you are running on a static surface
-The treadmill is in motion and you are running against it
-The treadmill is in motiion and you are running with it
In each of these cases you would feel a different amount of wind resistance, but that would not be enough to tell whether you’re running on a static surface in the wind, or a moving one in still air.
The differences between running on a treadmill vs a road are all attributable to things like:
-differences in gait
-incline of the surface
-mechanical quirks of the machine, such as inconstant speed
-wind resistance
-mechanical properties of the running surface
and probably a bunch of other stuff too - all of which might add up to quite a significantly different experience. What certainly does not make a difference is the fact that your centre of mass is not making progress across the floor.
I dont break off into a tangent, but this helps with a previous discussion I was having. My (sport science undergraduate) friend says that walking and running the same distance us exactly the same amount of calories because the work done is the same (I think she was trying to make the question engineer-friendly for me), but I disagree. By that logic, an hour on the treadmill should burn off none at all.
I don’t understand what you’re saying here. Under what logic would an hour on the treadmill burn no calories, and why?
An hour of standing still on a treadmill would require approximately the same amount of energy as an hour of standing still on the floor, but on most treadmills, you’d fall off the end long before the hour is up.
You don’t understand the logic. On a treadmill you are travelling a distance relative to the treadmill surface and are therefore doing work just the same as if you were travelling on the road.
OK, I hadn’t properly been thinking of the treadmill as an inertial reference frame. With that considered, the work done on the 'mill and the road would be the same, all other things being equal.
The other things not being equal, like incline, gait, surface, atmosphere, etc are what makes the energy required different. Using just work done to calculate energy required is an oversimplification of the problem. This bit is why walking and running dont use the same energy in real space, coupled with the biomechanics and chemistry of human physiology.
I get this now, right? I’m going to ace my treadmill problems exam tomorrow afternoon…oh, I dont have that exam tomorrow afternoon.
Yes, that’s right. The physics-oriented posts here have been saying “ignoring wind resistance etc”, in order to deal with the inertial stuff (because some people were getting that - the inertial stuff - wrong).
However, in real-world scenarios, that wind resistance and other non-inertial stuff is not insignificant - it makes a noticeable difference (just not really in an inertial reference-frame sort of way), so it can’t be ignored.
