Running in a vacuum

[MBennett]

There is something very odd going on with those news articles and the stated powers (hence my skepticism above). It states a total energy output of 81kJ over the 100m. But that would give an average power output of ~8.5kW. ... way above the supposed 'peak' output of ~2kW. Am I missing something obvious???

By my calcs, to use 81kJ over 100m would require an acceleration of 8.61m/s^2 if his mass is 94kg. Seems plausible if it takes him 1 and nearly a half seconds to hit full speed. Not sure how to describe their max power discrepancy though!

/edit - I am coming to the conclusion that the peak power is his actual KE power and the rest is what is lost to drag. It is just such an immense number it makes you think twice, for example I am a pretty mean rower and the max watts I can get out of a rowing machine about 850w, so Usian is banging out over twice this!

 

[Raymond Lin]

There's a big difference between "much faster" (the argument made) and "faster" (the argument you have just countered).

An athlete will run faster with a significant tailwind. The Olympics has a wind limit because it will make enough difference to be relevant in races timed to 1/1000th of a second. It could be considered "much faster" in that context, where 0.1s is a big difference, but it wouldn't be considered "much faster" in day to day terms. Maybe 30mph instead of 28mph.

So I think that Zefan has a good point when he counters the assumption implicit in the OP (that without air resistance a sprinter would be able to convert 12.5 times as much energy into motion) by arguing that if that was the case then a tailwind would have a much larger effect than it actually does.

Yes, I agree, 0.1seconds is not much faster in every day life. And I agree with you that 0.1 second is more significant a 100m race by an athlete.

But unless I am mistaken, except Zefan was referring specifically to a 100m race by an athlete in that post? which is what we are talking about, in the context of a 100m race? And not "day to day terms."

Unless the goal posts have changed ?

 

[Zefan]

The amount of difference it would make in reference to olympic level 100m sprint times is irrelevant, what is relevant is the figures suggested in the article.

 

[Kotu]

Surely a 30mph tailwind wouldn't make much difference, partly because:

1) Air is much lighter than a person, if pushing a person from behind then the net contribution of kinetic energy would be negligible.
2) The athlete would block the tailwind (people are not aerodynamic) so it would not effect the air resistance in front of the athlete.

You would probably need a 300mph+ tailwind to counter the air resistance, but the athlete would probably not be able to run properly with that kind of propulsion

 

[bledd]

Don't give it high revs or put it under unnecessary load for the first 1000 Miles.

This is what I was expecting from this thread

 

[D.P.]

They'd be no pressure in a vacuum, even if he had a breathing device he would die

Bit like being in outer space really

People survive a vacuum just fine. Space suits are worn to keep you warm or cool, you could jump out of a space ship and hod your breath for a minute before getting back inside.

T put it another way, the pressure difference between earth surface and space is1 atmosphere, equivalent to being 10m underwater.

 

[[FnG]magnolia]

I smell science and I don't like it

 

[Tefal]

This is a nice question, and very similar to some of the research I am doing at the moment (I work on road bike aerodynamics).

for the sake of the **** storm that it will create, which road bike ahs the best aero dynamics?

 

[FerretBoy]

I saw a calculator for cycling and a 6mph headwind doubles the energy required to maintain 14mph. I think they assumed a solid headwind though, rather than normal gusty wind.

 

[areksnumbr1sxylady]

What a complete load of ****. Does an athlete run 100m much faster with a 30mph tailwind? No.

Seriously, if you have to think about this for more than 10 seconds you need to have words with yourself.

Eh?

Have u tried running into 70mph Wind??

Did that slow you down?

 

[Genoma]

According to http://runnersconnect.net/running-training-articles/running-in-windy-conditions/

"A “substantial” wind (i.e. one approximately equal to the pace you are running at) will set you back 12 seconds per mile with a headwind, and aid you by 6 seconds per mile with a tailwind."

 

[gregorius]

All this talk of air resistance and wind assistance takes me back many years to A-level physics and using the full d/dt(mv) form of Newton's law to calculate things about helicopters...ah, so many years, so many roads...

 

[Zefan]

Eh?

Have u tried running into 70mph Wind??

Did that slow you down?

Yes I have actually, I do it on a nearly daily basis and yes, of course it does. Your point doesn't actually mean anything in the context of this arguement however.

 

[Angilion]

People survive a vacuum just fine. Space suits are worn to keep you warm or cool, you could jump out of a space ship and hod your breath for a minute before getting back inside. [..]

I wouldn't suggest trying that, though. It's not the instadeath explosion that it's sometimes made out to be, but it's not safe either. Especially if you hold your breath - having your lungs full of air would strongly increase your risk.

It's survivable, but it isn't "just fine". You'll pass out in much less than a minute (an astronaut was exposured to close to a vacuum in a training accident - he passed out in 14 seconds) because your body can't do gas exchange at all in a vacuum. It's not like holding your breath under normal pressure. You'll be totally oxygen deprived immediately, even though there will be some oxygen remaining in your blood. Fluids not contained by your body will boil quite quickly. Sweat wouldn't be a problem, but fluid boiling on the surface of your eyeballs would be. You'd also be at severe risk of the bends, very quickly.

If you take some deep breaths, breath out, close your eyes, jump towards a safe location and have someone there to bring you into a pressurised environment and apply relevant medical help...then you could probably survive a minute's exposure without permanent injury. Probably. That guy I mentioned above was exposed to near vacuum for 15 seconds. He lost his sense of taste for a few days (he said he could feel the water boiling off the surface of his tongue, which must have been rather unpleasant), but that was it. Give it a little more than 15s, or keep your eyes open, and you'll probably be blinded, probably temporarily, by damage to the surface of your eyes.

Of course, you could die immediately of a heart attack.

Survivable? Probably, if you know what you're doing and someone is there to take your unconscious body into a safe, pressurised location and give you medical treatment. Just fine? No.

EDIT: Also, spacesuits aren't mainly for temperature control. If you're in a vacuum, temperature control is the least of your worries because conduction and convection don't happen in a vacuum and heat loss by radiation is very slow for a human body. You'll be dead very quickly, but your corpse will take a very long time to freeze. You'd feel cold due to the fluid boiling on your exposed surfaces (I know that sounds wrong - "cold" and "boiling" don't usually go together but in this context they do), but you wouldn't actually be losing much heat.

 

[Mr Joshua]

I came here expecting a thread about breaking in a new vacuum cleaner.

 

[gregorius]

I came here expecting a thread about breaking in a new vacuum cleaner.

We could do that too. What do you reckon? Two weeks of light fluff only at two-thirds speed? Then we take it out to the garage mwahaha!

 

[rubberduck]

Surely this could be roughly tested on a treadmill?

Or take the max speed of usain bolt, get him to do the 100m sprint with a tailwind at this speed. If he is running at the same speed as the wind then he wouldn't be running into the wind and thus have very little wind resistance?

*has no fancy formula to compete with above *

Some good, 'out of the box thinking' here.... I don't think the treadmill thing would work however. Essentially on a treadmill you are still having to propel yourself forward in order to overcome the treadmill propelling your backwards. If you are pushing forward at the same speed as you are being pushed backwards you become stationary on the mill... However I still believe that you are having to push against the air in front of you and should it be removed you would then not have to push as hard in order to maintain equilibrium.

As for the second idea, I think this one actually could work... The only thing is that you couldn't use Usain's average speed but instead would have to adjust the velocity (in a wind tunnel say) with time to match his speed as he accelerates... The only problem is that this in turn would increase his speed so it would likely require a number of different iterations in order to match his velocity profile with that of the profile in the wind tunnel.

 

[Cold_And_Miserable]

You'd also be at severe risk of the bends, very quickly.

The bends aren't a problem since the pressure difference is just 1 atmosphere unlike rapidly surfacing from say 100m underwater.

Humans can survive for a minute in a vacuum as I said on page 1.

 

[413x]

did anyone else expect this to be about running in a vacuum cleaner?

yes! power consumption :O

 

[estebanrey]

Just read this article on the bbc http://http://www.bbc.co.uk/news/science-environment-23462815

Apparently when Usain Bolt ran 100m in 9.58 seconds, "8% of the energy his muscles produced was used for motion, with the rest absorbed by drag"

So I'm wondering what sort of speed could he achieve in a vacuum, if his muscles are using 100% of the energy for motion, would obviously need some kind of breathing device.

If that blows your mind, try this.....