Yttrium2
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heat capacity question from text
Suppose you are camping and you have to decide to bring a rock or water into your sleeping bag which would it be? Both the rock and the water are at
100 degrees C. Why?
Also, is it true that the lower heat capacity of Sacramento makes it hotter then the high heat capacity of San Francisco and the surrounding pacific
ocean? I'm meaning to say could specific heat be used interchangeably here?
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Yttrium2
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Are you ever able to tell how many joules of heat is going into a substance? How is this monitered?
I mean is there a way to say add 150 joules of energy
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j_sum1
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Short answer. Water holds a lot of heat. I am not sure off the top of my head if there are any common substances that have a higher heat capacity.
Water has a specific (aka heat capacity) of 4181 J/kg·°C. What this means is that it takes 4181 J of energy to raise the temperature of a kg of
water by 1°C. Equally it means that 4181J of energy is given off per °C that the water cools down.
A rock is typically 1/6 of that heat capacity. So, on a per mass basis the water is six times better.
However, a rock is typically 4-8 times as dense as water. So, what you lose by having a poorer heat capacity, you might gain through needing a
smaller volume.
Also it is not sloshy. And it can be heated to over 100°C if you like. (If you like burning your skin that is.) These might make it a more
convenient option for throwing in your sleeping bag.
As for the second part of your question, I have no idea what you mean.
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JJay
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One of the easiest ways to monitor how many joules of heat are going into a substance is to heat it with electricity. Experiments have been done where
mechanical energy was transferred into a substance using stirring paddles that were driven by a pulley attached to a long rope to which mechanical
energy was applied. So pulling the rope at 1 newton for 10 meters would put 10 joules of energy into the substance, resulting in a corresponding
temperature change. Of course, to get a really precise result requires accounting for mechanical losses and heat losses.
[Edited on 26-11-2015 by JJay]
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Fulmen
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j_sum: Most rocks have a density of 2.5-3kg/dm^3, few are denser than 3.5. So water wins either way.
We're not banging rocks together here. We know how to put a man back together.
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JJay
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Here is a video replicating Joule's experiment that demonstrated the equivalence between energy and heat.
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