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Question: Why do warm things get cold and cold things get warm when left out?
Things do not naturally go from one extreme to the other. If you put cups of boiled water with cups of ice cubes into a chamber, eventually everything in the chamber would be the same temperature. Nature eliminates extremes, yet extremes are around us all the time! This is so because energy heats places up. The sun heats up what it shines on because its light is radiant energy. Rain is cool because water vapor in the air was cooled by losing heat to adjacent colder air. As the vapor gets cool enough, water droplets precipitate from it, forming rain. Warm and cool air were brought into contact by motions of air masses driven by energy flows between warmer and cooler regions. All activity, from winds and storms to plants and animals is powered by energy flows. If temperature was uniform all over the earth, nothing could happen. The spinning of the earth prevents this, so that some locations cool off while others are heated by sunlight.
When warm things cool, they lose energy, which is then dissipated. But heat is only one kind of energy gradient. There is also energy holding matter together, in chemical bonds. So any material thing, including you, is an energy gradient. Energy gradients of importance to us are foods and fuels. We and our machines use these to power our activities. Foods represent renewable energy for us because they can be produced in farms and ranches. Fuels like coal, oil and gas are non-renewable. Solar energy and energies in winds and tides might be able to become renewable energies for our machines if we could develop technology to where it takes less energy to harness these energies than the amount we obtain from them.
All energy gradients will spontaneously get dissipated, as when hot things cool. They can be maintained only by adding energy to them. When you eat, you are supplying your body with energy for growth and maintenance. You might ask 'Why do all energy gradients tend to dissipate?' This is a profound question. It seems to be because our universe is very far from thermodynamic equilibrium, a condition where all matter would be divided into separate atoms scattered uniformly throughout. That's the state the universe is tending to reach, and energy dissipation serves that tendency.
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