Things you always wanted to know the answer to [Vol. 3]
Discussion
singlecoil said:
But the body of the chap on the moving escalator is mostly staying in one place, it's not going uphill. So he's not lifting his body weight, he's only lifting his legs.
It's the "only lifting the legs" that bothers. Unless you lift them both at the same time (jump) one leg will definitely be pushing harder than the other. But this happens going upwards as well. Hmm.RobinOakapple said:
In physics, AIUI, the classic definition of work is weight times height.
Yes. But time matters here because it determines the height.Imagine the extreme case where he is able to instantly jump from one step to the next.
At the instant he jumps he has to jump up the whole height of the step.
(He would do the jump, then wait for the step to move down by one step and then jump up again to the next one, jumping up a whole step's worth each time.)
But let's say the step is moving down one whole step every second.
And it takes him half a second to do move onto the next step.
That means the height he is rising each time would be half a step's worth.
Also I guess you might argue that he could do some weird stepping process where his upper body is entirely static with his legs smoothing everything out underneath such that the body doesn't rise and fall like a normal person's.
walm said:
RobinOakapple said:
In physics, AIUI, the classic definition of work is weight times height.
Yes. But time matters here because it determines the height.Imagine the extreme case where he is able to instantly jump from one step to the next.
At the instant he jumps he has to jump up the whole height of the step.
(He would do the jump, then wait for the step to move down by one step and then jump up again to the next one, jumping up a whole step's worth each time.)
But let's say the step is moving down one whole step every second.
And it takes him half a second to do move onto the next step.
That means the height he is rising each time would be half a step's worth.
Also I guess you might argue that he could do some weird stepping process where his upper body is entirely static with his legs smoothing everything out underneath such that the body doesn't rise and fall like a normal person's.
Not much upper body movement on this video which is the first one I could find on the subject that wasn't a 'fail' video.
https://www.youtube.com/watch?v=sA6RMSP8fRc
https://www.youtube.com/watch?v=sA6RMSP8fRc
RobinOakapple said:
Even if his body goes up and down by as much as you are visualising, he still isn't going to be doing as much work as the person who is going uphill. And anybody actually in the position of trying to maintain a steady height on a down escalator is going to quickly realise that bobbing his upper body up and down is costing him energy. He will even be able to feel it in his legs.
I have to admit that unless it is an instantaneous rise then yes, it will be less, you're right.And of course he will feel it in his legs just like you do when you walk up stairs - that's the point!
But it very clearly isn't zero - that just isn't how people walk up stairs.
They rise up, swing the leg they need to use next onto the next step and then rise up again. It's not a smooth continuous rise.
There is a long period with all the weight on one leg where that leg has already done the work and is just keeping the body at the same height relative to the step it is on.
singlecoil said:
Our posts were simultaneous but if you look at the video I linked above, you can see there is virtually no upper body movement, it's simply a question of moving the legs to accommodate the downward movement of the escalator steps.
Although it isn't a great angle I think you are right.Perhaps I have just been swayed by the fricking enormous steps they seem to have on the tube where they seem bigger than normal!
walm said:
singlecoil said:
Our posts were simultaneous but if you look at the video I linked above, you can see there is virtually no upper body movement, it's simply a question of moving the legs to accommodate the downward movement of the escalator steps.
Although it isn't a great angle I think you are right.Perhaps I have just been swayed by the fricking enormous steps they seem to have on the tube where they seem bigger than normal!
RobinOakapple said:
Part of the reason for starting this thread was that I have been considering getting an exercise machine and I'm trying to make sure I understand the physics principles involved. I'd like something that emulated the effort of walking upstairs.
If you come up with anything I'd be interested, I know I can climb stairs but that means having to walk down them again, and my knees tend to protest after a while. Upstairs is fine. What I need is a fireman's pole (I could practice my dancing then too).RobinOakapple said:
Part of the reason for starting this thread was that I have been considering getting an exercise machine and I'm trying to make sure I understand the physics principles involved. I'd like something that emulated the effort of walking upstairs.
You are still pushing upwards off a downward moving step. People use step machines to improve walking uphill fitness/general fitness. This one looks a bit expensive! http://www.fitness-superstore.co.uk/stairmaster-st...DoctorX said:
AstonZagato said:
Does exercise remove alcohol from your system any more quickly than normal metabolic processes?
No. Alcohol is cleared by enzymes, levels of which will not be affected by excercise. wiggy001 said:
Early drive tomorrow and tempted to go for a run? 
More that I'd had a couple of glasses at lunchtime and wondered if a gym session would help clear the body for my evening drive home. 
DervVW said:
Impasse said:
Why can't girls throw?
Gross generalisation, sure. But on the whole, girls don't ever seem to have a comfortable or particularly fluid throwing action.
Is this not due to the development of the upper body? More muscle mass etc?Gross generalisation, sure. But on the whole, girls don't ever seem to have a comfortable or particularly fluid throwing action.
DervVW said:
Impasse said:
Why can't girls throw?
Gross generalisation, sure. But on the whole, girls don't ever seem to have a comfortable or particularly fluid throwing action.
Is this not due to the development of the upper body? More muscle mass etc?Gross generalisation, sure. But on the whole, girls don't ever seem to have a comfortable or particularly fluid throwing action.
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