How many homes can you rent with free donuts?

You should get it a Covid-19 vaccine? Yes, it will protect you and others will help us overcome this pandemic and return to a more normal life. But wait! If you get vaccinated, you can even get a donut! At least that’s the deal Krispy Kreme is offering. After you get vaccinated, you will get a donut. And it’s not just one donut, but one every day. That’s a lot of donuts.

Okay, so how do you go about matching some of your physics estimates with your sweet tooth?

Let’s say all Americans with the Covid-19 vaccine receive (and eat) one donut a day. Of course, eating food gives you the energy to do things — that’s how food works. So let’s assume that all of these humans use that extra energy to pedal stationary bikes. All bicycles are connected to generators that are connected to the mains. What kind of power would that produce?

The first thing we need is the number of donuts we eat a day. According to the Centers for Disease Control and Prevention, from April 7, 63 million Americans were completely vaccinated. (Don’t worry too much about numbers; I’ll do all my calculations in Python so you can change the values ​​if that makes you happy. Also, I’ll assume that all these people will get their donuts. Every day.)

Then I need to know the amount of energy in the donut. According to Krispy Kreme’s website, ordinary stained glass is 190 calories. What the hell is a calorie? Well, it was created to describe the original calories changes in the thermal energy of different substances. Later, people used the term to measure the chemical energy that the body can gain from eating food. However, there is a problem: for some reason, calories appear on every food label, but those are actually kilocalories. This donut has 190,000 calories. It seems like too much for people to think of eating.

There is another unit of energy: the joula. Since it is a preferred unit of energy for physicists, I will use it. To convert between units, 1 calorie is equal to 4,184 joules.

What does this have to do with your daily life? Consider something you can do without much effort. Suppose you have a textbook on the floor and you pick it up to put on the table. Since you are exerting a force at a distance in the book, you need to change the gravitational potential energy of that book. The change in gravitational potential energy is equal to the mass of the book (about 1 kilogram) multiplied by the local gravitational field (g = 9.8 N / kg) and then multiplied by the change in height (about 1 meter). This will result in an energy change of about 10 joules. So this gives you a rough feeling about the amount of energy in a joule.

But what about power? Power is the rate of energy change. It tells you how fast you use energy. As an equation, it looks like this: