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Chemistry / What are calories?
« on: 23/09/2008 20:03:46 »
To actually answer the question. We use calories, defined in that rather odd way, because it seemed like a good idea at the time. Whether it's the energy in food or the energy used to heat something up, it's the same thing, that is energy. The choice of unit and how it is defined is arbitrary.
Just the same as a yard being defined as the distance between the King's nose and the tip of his out-stretched arm. We can then use the unit to measure the length of a field, or the length of a molecule. Scientists also like to use different units at different times so that the number looks good. So the length of a carbon to hydrogen bond may be described in "ångströms" as 1.06, rather than in metres as 1.06 * 10^-10, which is just too fiddly. That's what's going on with the difference in calaries refered to in food and in your science class.
Now if you actually asked what energy was, that would be difficult. Length is something we can experience directly and is easy to understand. Unfortunately we can't experience energy in the same way. Scientists generally hide behind definitions like, "energy is the ability to do work." Which is just another way of ignoring difficult questions and getting on with the day job.
Just the same as a yard being defined as the distance between the King's nose and the tip of his out-stretched arm. We can then use the unit to measure the length of a field, or the length of a molecule. Scientists also like to use different units at different times so that the number looks good. So the length of a carbon to hydrogen bond may be described in "ångströms" as 1.06, rather than in metres as 1.06 * 10^-10, which is just too fiddly. That's what's going on with the difference in calaries refered to in food and in your science class.
Now if you actually asked what energy was, that would be difficult. Length is something we can experience directly and is easy to understand. Unfortunately we can't experience energy in the same way. Scientists generally hide behind definitions like, "energy is the ability to do work." Which is just another way of ignoring difficult questions and getting on with the day job.