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Effect of temperature on increase in volume

  1. Jul 16, 2011 #1
    Hi,

    I have a fundamental question

    Density is mass divided by volume. As you heat something up the volume increases so the density decreases.

    Ok, but can anyone explain with a physical(intuitive) example: that is why is it that when you heat up something volume increases??Any intuitive example?

    Please help!!
     
  2. jcsd
  3. Jul 16, 2011 #2
    In a beaker take a little water and start heating. Before the boiling point is reached, pour a drop of blue ink in the water. See how the blue is spreading. You will notice that some sort of a ìcurrentî is generated in the water. The hot water molecules from the bottom of the beaker move up. This is called the convection current. The current keeps on circulating till the entire body of water heats up uniformly. Transfer of heat in liquids and gases always takes place through convection.

    Also, is it that, in the convection example;

    In a beaker take a little water and start heating. Before the boiling point is reached, pour a drop of blue ink in the water. See how the blue is spreading. You will notice that some sort of a ìcurrentî is generated in the water. The hot water molecules from the bottom of the beaker move up. This is called the convection current. The current keeps on circulating till the entire body of water heats up uniformly. Transfer of heat in liquids and gases always takes place through convection.

    Is it that, the rise of hot water is due to density decrease and the resultant effect of buoyancy?
     
  4. Jul 16, 2011 #3
    temperature is related to motion of particles, let's just call them electrons since I don't know much about this and the concept of the atom in my head is just a core with flying electrons around it...

    so, the warmer/hotter matter is, the larger (amplitude) the motion of the electrons and hence they tend to occupy more space...

    that's why solids not only expand, after that they tend to melt and liquids boils and after that evaporate...every molecule is simply needed more space for itself and its own energy overcomes other molecular forces of attraction...

    and yes the circulating vertical current is due to difference in density...

    ...that is why air-conditioning vents are typically placed at the top of walls, below the ceiling and eventually the cold air will want to come down and cool the entire height of the room

    ... and why some heating vents up north do just fine at the bottom of the wall along the floor and eventually the hot air will want to go up and warm up the entire height of the room.
     
  5. Jul 16, 2011 #4
    First of all, not everything expands when it is heated. Gases in rigid containers do not expand when heated, they increase in pressure but the volume remains constant. Water at 0°C does not expand when heated, it contracts until the temperature reaches about 3.984°C. After that it expands.

    Temperature is a measure of kinetic energy; that is, energy of motion. When the temperature of an ideal gas is increased, the molecules of that gas move faster and hit harder and more often. If the gas is not constrained, it will push whatever is around it away. In other words, the gas will expand.

    That's about as simple as I can make it. It's not really a simple matter.
     
    Last edited: Jul 16, 2011
  6. Jul 17, 2011 #5

    Mapes

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    Let's call them atoms or molecules. Your conceptual view is http://en.wikipedia.org/wiki/Bohr_model" [Broken].
     
    Last edited by a moderator: May 5, 2017
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