This Halloween, when you grab a candy bar, pay attention to the wrapper. In the United States, a “nutrition facts” label has been required for all packaged foods since 1994, giving the serving size and the amount of sugar, protein, fat, and sodium the food contains. But the most interesting bit is the metric for energy, which is listed as “calories.” What does energy really mean when it comes to candy?
In physics, the concept of energy helps us keep track of different types of interactions. We say energy is “conserved” for all interactions, meaning that if you calculate the total energy before and
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