if there was no gravity, would heat still rise?

[Paul the 6th]

Yet again sat at the back of a conference pondering existence, life and love...

If I was in space or an equally open space devoid of gravity, and I used my mig welder to weld a bit of steel on the exhaust of a 125 which has just had the cat removed to de-restrict it, would the heat still rise and possibly scorch the engine casing around the oil window, or would it disperse outwards in all directions equally?

And would the fact that space is a vacuum mean that the heat cannot disperse as there are no particles/atmosphere for the heat/vibration to travel through?

[Scoobs]

Gravity has nothing to do with the radiation of heat. If it were possible to weld in a vacuum, then there would be no heat transmission.


Or summat like that!

[Grant66]

heat causes expansion, expanded gas is lighter than none expanded gas, hence it rises (less affected by gravity than the surrounding non expanded gas). How are you defining up (rises) if there is no gravity? The heat would still radiate from the hot surface in all directions, if this radiation was hot enough it would heat the engine casing. Would have thought it would melt as opposed to scorch as there would be no oxygen for the combustion.

Can you tell its a slow day at work.

[hardhat_harry]

Space isn't a complete Vaccuum anyway.

Also look at the big red glowy thing in the sky (I think its called the sun) can you feel its heat.

[keith_d]

Heat doesn't rise! Hot air rises due to changes in density relative to the surrounding air, which would not matter in zero gravity.

I've not tried it, but I'd imagine that arc welding in a vacuum would be difficult because the arc between the electrode and the substrate is made up of ionised atoms from the surrounding gas (air, carbon dioxide or argon). You would probably need to add a gas supply to get any kind of reliable arc.

On the plus side, once you had melted the metal you wouldn't have to worry about oxidation.

Keith.

[punyXpress]

Space isn't a complete Vaccuum anyway.

Also look at the big red glowy thing in the sky (I think its called the sun) can you feel its heat.

That's just a nasty rumour put out by the Global Warming brigade - flat earth society subsection. ;)

[ophic]

it can't rise, cos in space there is no "up". QED :cool:

[SoulKiss]

it can't rise, cos in space there is no "up". QED :cool:

An there is no Ice Cream either

"In Space, no-one can eat Ice-Cream"

Also why is it assumed that no gravity == a vacuum?

Theres no gravity in the International Space Station, yet they have air.

Oh and Paul, if you are so bored, check your PM's - lol

[ophic]

An there is no Ice Cream either

"In Space, no-one can eat Ice-Cream"
well that's my holiday in space cancelled :(

[thor]

Heat is energy in the form of vibration of atoms in a matrix (solids), the movement of atoms in a fluid, or electromagnetic radiation. There are 4 ways for heat to travel, respectively.

In solids: Vibrating atoms or molecules vibrate the next one along like a vibration on a stretched string. This is called conduction. Its not affected by gravity. This is why a radiator is hot when it is filled with hot water.

In fluids: Atoms/molecules move more quickly and therefore occupy more space. Therefore the same weight of stuff takes a larger space. Given a fluid that has an even pressure, the lighter bits rise to the top, because the heavier bits sink. This is called convection. This is affected by gravity. Also, the speeding molecules can mix with the other slow ones. This is called diffusion. This is not affected by gravity.

In a transparent medium (eg, air or a vacuum) electromagnetic radiation travels through the medium, and can make atoms and molecules start wiggling if they absorb the radiation. This is called radiation. It is not affected by gravity.

If you were in the space station, in air but no gravity, then heat would spread out in all directions, via all 4 mechanisms except convection. If you had no air, then its conduction and radiation only. If the hot and cold bits are not touching, then its radiation only.

[yorkie_chris]

Gravity has nothing to do with the radiation of heat. If it were possible to weld in a vacuum, then there would be no heat transmission.

it's possible to weld in a vacuum :)

[Amplimator]

Dunno the answer to your question but i do know that with no gravity when nekkid me nuts would get in the way! would be like having a constant semi with ya testicles either side of it too. It would look a bit like standing on ya head nekkid. Try it.

Also the term 'its a floater' would be more realistically suited.

HTH

[Jabba]

Thor is on the right lines. The lack of gravity would prevent convection. Other means of heat transfer along a hot----->cold gradient would still work.

[Bluefish]

yeah you can weld in a vacuum, cos i'm listening to the Halo series of audio books at the mo and they just did it. ;)

[keith_d]

Thor is on the right lines. The lack of gravity would prevent convection. Other means of heat transfer along a hot----->cold gradient would still work.

Yes, but he forgot to mention that in conducting solids there's not just lattice vibration, there's electrons carrying energy about too.

[Ed]

What a bunch of smartarses we have on here:D

[MisterTommyH]

Heat doesn't rise!

Keith.

Lol. That was my physics teachers favourite rant. So much so we used to ask if heat rises every lesson.

"heat does not rise! Hot fluid rises!"

But what he said, 'it' rises because the particles are less dense (I.e. Less massive) and therefore the more dense (cooler) part if the fluid is more attracted to the earth.

Just because you are in space doesn't mean theres no gravity, how do you think we orbit the sun. The hot fluid would radiate away from whichever body caused the greatest gravitational force, although in practice the forces would be so negligible you would get a uniform distribution.

On the other hand if you mean if gravity didn't exist you're talking about changing all the laws of physics... Would heat even be possible in that 'world'?

[Paul the 6th]

So my engine casing should be alright when I take my Chinese Sanya sy125 for an interspacial adventure & realise I could do with a bit more oomph?

[Viney]

Would a vaccum cleaner work in a Vaccum, thats my question

[Paul the 6th]

working on another conference at the barbican so I'll prolly post another random question later today... :)

[yorkie_chris]

Would a vaccum cleaner work in a Vaccum, thats my question

No

[Viney]

NoWhy not. A Simple No is not an answer.

And Paul the 6th. If youa re still at the Barbican, then you are about 100 Yards from my office

[Paul the 6th]

sorry mate, I escaped that cursed place yesterday evening at 5pm and walked through my front door in york at 9:15 :D on wednesday everything worked fine, but yesterday morning in the other cinema (cinema 2) the kramer video wouldn't output signal without a purple tint (tried 8 different vga cables and both video outputs to no avail), the 7 inch lectern and top table monitors started doing weird things when we finally got the signal down to the front stage, then the powerpoints wouldn't link together (which is the old school way of doing things seeing as the kramer was busted)... PolicyReview.tv were there filming on both days - wednesday all their kit worked, yesterday half of it didn't and then 2 laptops were stolen! Cursed venue I tell you!

Could be there again in a few weeks mebbeh

[ophic]

A Simple No is not an answer.
Yes it is :p

[thedonal]

If there was no gravity, nothing would rise.

Because without a point of reference such as a centre of gravity, up-down-left-right etc are relative to the perspective of the viewer and would be anyway- if you stand on your head, which way is up?

[punyXpress]

Ah, but you still throw up when you stand on your head ? :confused:

[L3nny]

An there is no Ice Cream either

"In Space, no-one can eat Ice-Cream"



http://www.whatscooking.info/images/AstronautIceCream_Napoleon_Web.gif