How come cold things sink and warm things rise? It’s always warmer on the top floor of my house while the bottom floor is freezing. Tornados are caused by cold and warm air joining together violently. I can’t think of any form of matter known to man where the warm parts sink and the cool parts rise (water and ice don’t count. It’s known that cold water sink until ice crystal form which then float to the top). I suppose it has something to do with gravity, but I need the connection explained to me.
It’s density, and if I didn’t have it in spades, I could explain it better…
An increase in heat makes matter expand…when it expands it gets less dense…which means it’s lighter per unit volume than when it’s colder. Hence the pull of gravity is less and it rises relative to the stuff around it.
BTW…cold ice rises in warm water because it’s less dense than the water due to its structure…has nothing to do with temperature.
In really rough terminology, cold things contract, warm things expand. (Ice differs because the ice crystals formed at the freezing point are larger than the water from which they are made.)
Take a cubic foot of air. Heat it, it expands. Chill it, it contracts. The contracted, cooler air is now denser than the warmer, expanded air, and is heavier per cubic foot that the warmer air. (Remember that as your cooling air contracted, other air pushed in to fill the gap left by the contraction.)
Now your denser, heavier air is going to fall in relation to the warmer, expanded, lighter air. Hence, warm air rises by being pushed out of the way by the falling cooler air.
dududu
well, it just go’s to show that i need to think thies questions through before i waist everyone’s time. sorry.
Cold air sinks and warm air rises because cold air is more dense than warm air. That means cold air weighs more per unit volume than warm air. The increased weight causes it to sink in warmer air. This is what bouyeancy is all about. Any time an object is placed in a fluid if it weighs less per unit volume it floats, more per unit volume it sinks.
As for why warm things are less dense, you have to think what warm means. Heat, on the molecular level, is the average kineic energy of the molecules. Let’s assume we are dealing with a monoatomic ideal gas for the moment in which all the molecules have the same mass. Now kinetic energy is proportional to velocity. So when you heat this gas you increase the velocity of the molecules. If you heat within a fixed volume it will cause the pressure to increase (pressure can be thought of as the number of molecule tto wall collisions). If you heat with constant pressure (a useful description because differing pressures equalize rapidly within local phenomena such as a house or thunderstorm) the volume of the heated gas increases. Since the volume increased but the mass didn’t it became less dense and rises above the cooler air.
I hate it when I compose a reply then someone beats me to the answer, but I going to post anyway, so take that 