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Author Topic: Why do objects get bigger as they heat up?  (Read 1351 times)

Offline thedoc

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Why do objects get bigger as they heat up?
« on: 25/09/2015 17:50:02 »
Katie Marsden asked the Naked Scientists:
   
Why do objects get more massive when they heat up? Why isn't it just their kinetic energy that increases as more energy is pumped into the system?

What do you think?
« Last Edit: 25/09/2015 17:50:02 by _system »


 

Offline lightarrow

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Re: Why do objects get bigger as they heat up?
« Reply #1 on: 25/09/2015 18:22:26 »
Why do objects get more massive when they heat up? Why isn't it just their kinetic energy that increases as more energy is pumped into the system?
They don't get more massive (their weight don't increase). It's their volume which (usually) increases with temperature.
"Usually" because it's not always true for all substances and at every temperature intervals. For example, water volume decreases when you heat it in the interval between 0C and 4C.
But there are several other substances/materials which show such unusual behaviour, in some interval of temperature.

About the rest of what you say it's a bit more complicated, it has to do with how atoms/molecules potential energy depends on temperature, for condensed matter, and to which are the degrees of freedom involved, for a gas. Are you more interested in having an answer for solids, liquids or gases?

--
lightarrow
« Last Edit: 25/09/2015 18:31:33 by lightarrow »
 

Offline evan_au

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Re: Why do objects get bigger as they heat up?
« Reply #2 on: 26/09/2015 12:34:18 »
Quote
Why do objects get more massive when they heat up?
Things do get slightly more massive as they heat up, but the effect is so small that you could never measure it on Earth.

I think the amended title is the intended question:
Quote
Why do objects get bigger as they heat up?
You can imagine matter as made up of atoms, connected by little springs, jiggling around all the time.
Heat is a measure of how much they jiggle around; more heat=more jiggling.

Like real springs, there is a limit to how much you can compress the distance between atoms. However, there is no real limit to how much you can increase the distance (until the spring breaks, and the atoms go their separate ways, as a liquid or a gas).

So when you make the atoms jiggle more, their average separation increases, causing the object to become bigger. 

Quote
Why isn't it just their kinetic energy that increases as more energy is pumped into the system?
You can increase the kinetic energy of an object as a whole, by putting it into a plane or a space rocket, etc. This doesn't increase the temperature, as the atoms are still jiggling with the same energy as when the object was stationary (ie it has the same heat content). This requires a very ordered and uniform application of kinetic energy to the whole object.

If you heat up the object with a flame, the heat (random movement of molecules in the flame) is transferred to the object (as random movement of atoms in the object). This is a very disordered application of energy to the object. It will not produce an overall movement of the whole object*.

The laws of thermodynamics place fairly strict limits on highly disordered energy (like heat=high "entropy") being transformed into highly ordered forms of energy (like kinetic energy of the whole object=low entropy). 

However, highly ordered energy (like the motion of a spacecraft in orbit) can be fairly easily be transformed into heat (such as when a spacecraft re-enters the atmosphere).

* I am assuming that you are not heating a cannonball by placing it in a cannon...
 

Offline mathew_orman

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Re: Why do objects get bigger as they heat up?
« Reply #3 on: 27/09/2015 09:41:52 »
Because on atomic level oscillations of electrons and atoms creates the growth of size...
There is a difference between atomic oscillation energy and and particle velocity one...
Atomic particles can have both types at the same time...
 

Offline Thebox

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Re: Why do objects get bigger as they heat up?
« Reply #4 on: 27/09/2015 16:50:01 »
MOD EDIT: Yo, Box! You can spout all the non-science you want in your own threads, but stop answering other people's questions with your alternative theories. This adds little to the discussion and distracts from the original question. I will not hesitate to remove your answers to other peoples' questions if they are irrelevant and confusing.

Point taken but my answer meant the same thing, I will reply with a question then.


When the atoms are under kinetic excitement and produce heat/energy, what polarity is the heat/energy output from the kinetic action?

 

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Re: Why do objects get bigger as they heat up?
« Reply #4 on: 27/09/2015 16:50:01 »

 

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