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?

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.

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]

Originally Posted by 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.

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

[SoulKiss]

Originally Posted by ophic

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

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]

Originally Posted by SoulKiss

An there is no Ice Cream either

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

well that's my holiday in space cancelled

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.