How to Measure the Calories in a Candy Bar—With Physics!

This Halloween, when you drawback a candy bar, salary attraction to nan wrapper. In nan United States, a "nutrition facts" explanation has been required for each packaged foods since 1994, giving nan serving size and nan magnitude of sugar, protein, fat, and sodium nan nutrient contains. But nan astir absorbing spot is nan metric for energy, which is listed arsenic "calories." What does power really mean erstwhile it comes to candy?

Flavors of Energy

In physics, nan conception of power helps america support way of different types of interactions. We opportunity power is “conserved” for each interactions, meaning that if you cipher nan full power earlier and aft thing happens, that worth will beryllium constant.

During these interactions, power tin alteration from 1 type to another. I for illustration to deliberation of these types arsenic “flavors” of energy. There's nan power of a moving object, a spirit we telephone kinetic energy. There's power stored successful nan gravitational field, a spirit we telephone gravitational imaginable energy. There's power stored successful nan relationship betwixt 2 charged particles, aliases electrical imaginable energy. And of people erstwhile things get hot, there's an summation successful thermal energy.

All types of power are interchangeable. How do you alteration power from 1 spirit to another? I mean, we do this each time erstwhile we brew a cookware of coffee. When current—electrical energy—runs done a wire, that ligament gets hot. You tin usage this power to summation nan somesthesia of water. (That’s thermal energy.) We tin cipher nan electrical power by measuring nan electrical existent and voltage crossed nan wire. This will beryllium adjacent to nan alteration successful nan thermal power of nan water.

There's besides a relationship betwixt mechanical power and thermal energy. Imagine that you person a vessel of h2o and you want to usage immoderate spinning paddles to operation it. Your paddle strategy has 3 parts: nan paddles astatine nan bottom, a magnitude of statement successful nan middle, and a dense weight that slides on nan statement from apical to bottom. As gravity pulls nan weight down on nan rope, nan paddles rotation and push nan water. This causes nan h2o to move, but nan frictional relationship besides heats nan h2o up. The alteration successful nan gravitational imaginable power of nan weight arsenic it moves down nan statement is adjacent to nan alteration successful thermal power of nan water. Energy from mobility has turned into power energy.

The Joule, nan Calorie, and nan (Other) Calorie

In physics, our preferred portion for power is nan joule. Historically, nan worth of 1 joule could beryllium defined arsenic nan power that a unit of 1 newton produces erstwhile moved 1 meter. A joule is besides adjacent to nan electrical power from a existent of 1 amp and voltage of 1 volt for 1 second.

It tin beryllium difficult to get a consciousness for this unit, truthful effort this elemental experiment: Take a textbook and put it connected nan floor. Now prime it up and put it connected a table. Since nan book moved up, it gained much gravitational imaginable energy. The power summation is astir 10 joules. (The existent worth depends connected nan tallness of nan array and nan wide of nan book.)

The calorie is different portion of energy. It comes from nan thermodynamic broadside of energy, truthful it has to do pinch changes successful temperature. The worth of a calorie is adjacent to nan power required to raise 1 gram of h2o by 1 grade Celsius.