Simple physics question..

[ringo]

Hi guys!

This is great - since registering here, I can ask all the dumb questions that I was always to embarassed to ask while in school. I appreciate all your help and answers.. thanks!

This question concerns the methods of energy transfer - convection, conduction and radiation. Am I correct in saying that radiation is like how we receive the heat from the Sun?

Conduction would be if I were to put an egg in a frying pan.. ie, the two mediums have to be in physical contact.

Convection is when the energy travels through a medium - is that correct? I can't think of any examples of convection off the top of my head.

That's my basic understanding of the methods of energy transfer. How accurate am I in my understanding?

Thanks in advance!

Ringo

 

[Terry]

Convection is heat transfer by fluid motion. For instance, when you boil water in a pan, the water at the bottom is heated by conduction from the metal. But the bulk of the water is heated by the convective flow of the less-dense hot water up through the liquid.

 

[kalen]

And conduction would be when the energy travels through a medium. For example, when the bottom of your frying pan gets hot, the rest of the pan heats up, as well.

 

[homer]

convection, conduction and radiation. Am I correct in saying that radiation is like how we receive the heat from the Sun.

Ringo

I think so , which is why a vacumn flask is silvered on the inside to stop radiation . The vacumn stops conduction I would guess and sealing it prevents convection . Of course the seal is not perfect .

 

[GodMark2]

Hi guys!

This is great - since registering here, I can ask all the dumb questions that I was always to embarassed to ask while in school. I appreciate all your help and answers.. thanks!

This question concerns the methods of energy transfer - convection, conduction and radiation. Am I correct in saying that radiation is like how we receive the heat from the Sun?

Conduction would be if I were to put an egg in a frying pan.. ie, the two mediums have to be in physical contact.

Convection is when the energy travels through a medium - is that correct? I can't think of any examples of convection off the top of my head.

That's my basic understanding of the methods of energy transfer. How accurate am I in my understanding?

Thanks in advance!

Ringo

note 1: something hot simply has more kenetic energy in it's atoms.

Radiation: Put the kenetic energy into a photon, let the photon travel, then have the photon put the kenetic energy back into something physical.

Convection: Keep the kenetic energy in something physical, then simply move that physical thing.

Conduction: Have the physical thing with the kenetic energy transfer it directly to an adjacent physical thing.

Of course, at the sub-atomic level, only the first two ever actually happen. The other is simply a way for non-savants to do the bookkeeping of the first over huge numbers of objects without going crazy.

 

[Soapy Sam]

Ringo- You have conduction and radiation right. Remember that air is also a medium, so heat transfer in a fire is by a mixture of conduction and radiation. In a vacuum (like space), there is no air, so heat transfer is only by radiation, unless the two objects are physically in contact (conduction).
An example of convection would be the way hot water rises in a warming pan. It's almost certainly convection movement in the Earth's Mantle which drives Plate Tectonics. A neat illustration of convection cells can be made by putting a little curdled milk in a cup of hot coffee- The milk flocculates and you can easily see the action of convection. If it has time to evaporate a bit, a skin forms. You can see the convection cells break it up and slide bits around, just like continental plates. Don't drink it.

Note that while both conduction and radiation can work in outer space, convection will not work in zero gravity (free fall), because there is no preferred upward direction for the hotter fluid to go. So outward conduction takes over as the main heat loss mechanism. This is one reason why boiling an egg while skydiving is difficult.
Convection will work in a spacecraft that is accelerating, or rotating, because inertia provides a down and up direction, so the lighter stiuff can rise. This bothers me for some reason.

 

[Ziggurat]

This is one reason why boiling an egg while skydiving is difficult.

I just wanted to highlight this sentence because I like it so much.