# how long would a match burn on the space shuttle?

#### bwanaaa

##### Senior member
In the absence of gravity, the heated air and smoke would not rise but merely accumulate around the flame. In the abscence of an air current, the smoke would put out the match. It would look cool-rather like those balls of water that the astronauts caught in their mouths. gotta look on u tube.

#### SuperFungus

##### Member
Like the guy in the video says, it would burn fine just as a sphere and slower. So i would guess that it would burn longer in microgravity than it would in Earth gravity.

http://webexhibits.org/causesofcolor/3B.html
This article also supports this, the flame is smaller and hotter, but burns slower acording to it.

#### Matthias99

##### Diamond Member
In the absence of gravity, the heated air and smoke would not rise but merely accumulate around the flame.

I'm not a physicist... but wouldn't you still get some convection due to the hot air near the flame trying to expand?

It would probably tend to 'recirculate' more than in normal gravity, but a lot of the hot gases/smoke should expand away from the flame and get replaced by denser, cooler air.

#### Scarpozzi

##### Lifer
So if the smoke and gasses don't rise when the flame burns....

What happens 20 minutes after you eat a Taco Bell 1/2 pound burrito? Do the other asstronauts smell the fart or does the gas gravitate around your tail?

#### Smilin

##### Diamond Member
Originally posted by: Scarpozzi
So if the smoke and gasses don't rise when the flame burns....

What happens 20 minutes after you eat a Taco Bell 1/2 pound burrito? Do the other asstronauts smell the fart or does the gas gravitate around your tail?

On earth, gasses rise not to get away from gravity. They rise because the warm gas has expanded and denser gas is pushing in. It just so happens the denser gas is being pulled down by gravity. Net result is the lower pressure gas goes up while the denser gas goes down.

In microgravity the warm gas would still be lower in density than the surrounding gas. "convection" will still occur it just won't happen "up".

As for the fart... yes other astronauts would still smell it. The stink isn't being distributed by your warm fart rising so much as by "brownian motion" (hehe seriously).

#### silverpig

##### Lifer
The smoke and hot air would dissipate diffusively.

#### bobsmith1492

##### Diamond Member
Originally posted by: Matthias99
In the absence of gravity, the heated air and smoke would not rise but merely accumulate around the flame.

I'm not a physicist... but wouldn't you still get some convection due to the hot air near the flame trying to expand?

It would probably tend to 'recirculate' more than in normal gravity, but a lot of the hot gases/smoke should expand away from the flame and get replaced by denser, cooler air.

That was my first thought - convection. However, after a second of reflection, I realized that convection (movement of air/fluid) works because the hot air is less dense and therefore rises since GRAVITY pulls more on the cooler air down around the hot air.

But, there's no gravity in space; therefore the hot air would merely expand in a bubble around the heat source, and no cool air would come in from below - no convection would occur without gravity.

Does that make sense?

#### Megamixman

##### Member
Convection does not work because Gravity is pulling on the more dense air more then the less dense air. Gravity merely aids in doing this. Diffusion on the other hand works on the basis that because all systems try to move to a lower energy state. By doing so they increase the entropy of the universe. So when you have smoke densely packed around the match, you have a highly organized system. The system will try to move to a state of higher entropy, which is a more diffused state in which the air is more homogeneous. In other words the smoke dissipates because this is a state of higher entropy.

#### CycloWizard

##### Lifer
Originally posted by: Smilin
On earth, gasses rise not to get away from gravity. They rise because the warm gas has expanded and denser gas is pushing in. It just so happens the denser gas is being pulled down by gravity. Net result is the lower pressure gas goes up while the denser gas goes down.

In microgravity the warm gas would still be lower in density than the surrounding gas. "convection" will still occur it just won't happen "up".

As for the fart... yes other astronauts would still smell it. The stink isn't being distributed by your warm fart rising so much as by "brownian motion" (hehe seriously).
I'll never forget my first time going to a professor to ask a question. He, in his infinite wisdom, said 'If I fart and you smell it a few seconds later, that's diffusion. If I fart and I turn a fan on behind me, you smell it right away. That's convection.'

Pressure gradients (resulting from density gradients) are not the only driving force for convection. Gaseous diffusive systems will have important convective effects if non-equimolar exchange is occurring in the low-pressure (ideal gas) limit. In other words, if two moles of A are diffusing down a tube and react at the end to form one mole of B, convection terms will have an impact on the system's behavior. This is still the result of a pressure gradient, but not one resulting from a mass density gradient, as B must have the same mass as 2A. One might call it a molar density gradient.

#### dkozloski

##### Diamond Member
All you have to do to keep the match lit is to wave it around a little bit.

#### SuperFungus

##### Member
Not even that, like many above and the man in the video have said diffusion will still occur and is enough to sustain the flame.

#### oynaz

##### Platinum Member
Since this is Highly Technical:

The astronauts aboard the space shuttle is not in microgravity, they are in free fall.

And there is gravity in space. "There is no gravity in space" is a misunderstanding.

#### SuperFungus

##### Member
Since this is Highly Technical:
The astronauts aboard the space shuttle, like most objects in orbit, are indeed in freefall, and thus microgravity;

"But since they're all falling at the same rate, objects inside of the Station appear to float in a state we call zero gravity (0g), or more accurately microgravity (1x10-6 g.)"

http://www.nasa.gov/centers/glenn/research/microgex.html

There is still gravity, and they are in free fall. However, the gravitational forces affecting the flame's motion (and the motion of it's exhaust gasses) in relation to the candle are all minimal, the only 2 massive bodies near the shuttle are earth and the sun, and both's effects are eliminated in this frame of reference by the process of orbit because the candle and flame are free falling in the exact same way. Simply put, free fall is just another name for microgravity.
Of course this IS highly techincal, maybe you know something NASA doesn't? hehe I kid, clearing up that there IS gravity in space is important, thanks, but assuming no gravity wouldn't really change anything in this case.