It doesn't appear to be convection, as there are no moving objects (or are there); probably not radiation, so it is conduction?
I am confused because it seems that the molecules in the stove does not move and therefore don't conduct.
$\begingroup$
$\endgroup$
4
asked Apr 23, 2015 at 21:46
-
1$\begingroup$ How do hot objects 'burn'? Do you mean, how do they transfer heat? If so then most are through conduction. Induction hobs are also increasingly common. $\endgroup$– lemonCommented Apr 23, 2015 at 21:52
-
$\begingroup$ Are you asking why a stovetop gets hot, or how it burns? Because if you really do mean burns, then I am confused by the question. $\endgroup$– Mike BellCommented Apr 23, 2015 at 21:52
-
$\begingroup$ @MikeBell How do they transfer heat energy? $\endgroup$– HyperLuminalCommented Apr 23, 2015 at 22:11
-
1$\begingroup$ The molecules in a stove do move. They jiggle about a lot and this jiggling of stovetop molecules can affect adjacent skin molecules. $\endgroup$– RedGrittyBrickCommented Apr 23, 2015 at 22:24
Add a comment
|
3 Answers
$\begingroup$
$\endgroup$
1
When you put the pot on the stove, the heat from the stove is somehow getting to the pot, which gets hot.
- The pot and the stove are obviously in contact with each other. Therefore conduction plays a role here. If you have an old pot, with a warped bottom, it will heat up slower, because the contact surface between pot and stove is smaller.
- When you hold your hand over the stove (not touching it), you can feel the heat. The air above the stove is heated and because it is a gas, moves upward. This is convection. The bottom of the pot and the surface of the stove are not 100% flat. That's why there will be little pockets of air underneath the pot, even if you place it on the stove.
- If you heat up the stove as much as you can, it will glow red. This is a visible sign of radiation. I'd assume that even if not visibly glowing, the stove radiates heat, too. In those areas where the stove and the bottom of the pot are not in contact, radiation transports heat from the stove to the heat.
As you can see, all 3 kinds of heat transfer are involved. Conduction certainly does the most part, which is why you want to have pots with flat bottoms, to make best contact with the stove.
-
$\begingroup$ I doubt that anybody owns a stove-top and pans that are machined so perfectly as to exclude all gas molecules between the pan and the stovetop. Also, radiation does not require separation between the two. I would wager that from the stovetop to the pan, much of the energy is transferred by radiation and by conduction through a layer of gas, and some by conduction from stove-top direct to the pan, and maybe a tiny-tiny amount could be attributed to tiny-tiny convection currents within the gas layer. $\endgroup$ Commented Apr 24, 2015 at 16:01
$\begingroup$
$\endgroup$
Here's a simple mental picture to have of a how a burner on a stove heats up water in a pot (which is sitting on the burner). (In what follows, I will use the term "molecules" for both molecules and atoms.) Also, keep in mind that thermal conduction is different than electrical conduction. One (electrical conduction) concerns the flow of charge, so in this type of conduction, particles actually flow from one place to another. The other (thermal conduction) concerns the flow of heat (or energy), but no particles or molecules are flowing from place to place in this type of conduction.
1) When you turn on the stove, an electric current begins running through the burner (or through a resistor in the burner). Due to the resistance in the burner, the current causes the burner to heat up (just like any resistor warms up when you send current through it, due to collisions caused by the charges trying to move through the material in the resistor).
2) As the burner begins to warm up, the molecules in the burner are now vibrating more rapidly than they were initially. Sometimes these rapidly-vibrating molecules near the surface of the burner will collide with molecules on the bottom of the pot. These collisions transfer energy from the stove top (the burner) to the pot via thermal conduction.
3) As molecules on the bottom of the pot gain kinetic energy from the stove, these molecules in the pot begin colliding with other molecules in the pot, transferring heat throughout the pot, again via thermal conduction.
4) "Pot molecules" near the water on the inside of the pot can now begin transferring their kinetic energy to the water molecules via collisions (because all the molecules are vibrating). This causes water molecules at the bottom of the pot to start moving around more quickly, corresponding to an increase in the temperature of the water. Because the water molecules have much more freedom to move around than do the stove and pot molecules, the faster-moving water molecules at the bottom of the pot can now begin transferring their kinetic energy to the rest of the water via both conduction and convection.
$\begingroup$
$\endgroup$
Stoves and other hot objects heat up, but don't burn. Burning is very different. Burning is a chemical reaction. In the example of stoves, they work by conduction.
