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We love the good things we get from using energy, and we use a lot of it. When we “use” energy, it doesn’t disappear, but it is changed to a form that is less useful, and eventually, it becomes totally useless to us. So, we spend a lot of effort into finding sources of concentrated energy that we can use. How rapidly we use energy is called power. You could use most of the energy in your food to sprint down a racetrack, generate high power, and then rest up afterward with low power, or you could use the same amount of energy in the same amount of time by walking steadily with intermediate power output. We measure energy in joules or calories or kilowatt-hours, and power in watts or calories per day or in other ways. Food burning inside us averages about 100 watts, but in the US the energy use outside is more than 100 times larger, and almost everyone almost everywhere uses far more energy outside than inside—the global average is roughly 25 times more energy use outside than inside. And, for most of the world, the energy used is primarily fossil fuels—85% in the US, and similar for most places. Typically, this is about 10% of the economy. So, we spend a lot of money to get good things from energy.
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