If Leftover Candy could power a Cellphone

If Leftover Candy could power a Cellphone
November 7, 2016

Halloween has come and gone, and if your Halloween candy bowl looks like mine, all of the Kit Kats, Twix and Butterfingers are long gone, leaving nothing but the junky candy that you might spend the next month lacklusterly picking over.

So this year, I thought I might see what other things we could theoretically do with the energy stored in those spare sweets.

Note: These calculations rely on a few assumptions, most importantly that it would be possible to zap Halloween candy into Calories that we can use however we want without losing any energy. I will point out these simplifications and what they do when they pop up.

Hot Water

2The original definition of the calorie, what we call the “kilocalorie” or “dietary calorie” today, was grounded in something we can easily see. One Calorie was the amount of energy required to heat one kilogram of liquid water from zero degrees Celsius to one degree Celsius.

It is very specific because the properties of water vary at different temperatures, but for our purposes, one liter weighs close enough to one kilogram and one Calorie can heat that liter close enough to one degree at any temperature. So we can say one calorie can heat one liter of liquid water by one degree Celsius.

So let’s say instead of eating the remainder of your Halloween candy, you opt for asparagus. You decide to heat four liters of water to a boil using the energy housed in fun size Mounds bars. Each bar has 80 calories, which means it can heat one liter of water by 80 degrees. To heat all four liters from 20-degree room temperature to boiling at 100 degrees, you would need 4 Mounds bars. The pot and the asparagus will soak up some of that heat so you might need a fifth Mounds to get that hot meal.

If five fun size candy bars can boil a pot of water, you might be asking yourself how we can eat a cheeseburger without melting, but the body has plenty of molecular machines that require energy on top of the walking and talking we do every day. In fact the average human needs about 2,000 Calories every day to keep everything running smoothly.

Working Out

Clean and JerkAnother plainly visible form of energy is physical work, moving an object from one place to another. Work is expressed as force over a given distance. The primary metric unit for work is the Joule, a combination of other metric units that can be written as kilograms times meters squared, divided by seconds squared or as Newtons, a unit of force, times meters.

Each dietary calorie is equal to 4,184 Joules of mechanical work. So if we follow our perfect energy conversion from the last example, we can use Whoppers to lift some weights. 

The work required to lift an object straight up in the air is just the force you use to lift it, multiplied by the distance you lift. When you lift at a constant speed, the force you use to lift an object is equal to the force of gravity on that object.

So imagine you are doing a clean and jerk, the exercise weightlifters do in the Olympics. You lift 50 kilograms from the ground, up to a height of two meters and then you drop it back to the ground. The force of gravity on the weight is just the 50 kilogram mass, multiplied by the acceleration of gravity, which is about 10 meters per second squared, for a force of 500 Newtons. Multiplied by the distance of two meters, each rep requires 1,000 Joules.

A single snack size pack of Whoppers has about 32 Calories, and if each calorie contains 4,184 Joules, that pack of Whoppers has 133,888 Joules of energy. The energy from that one pack could cover 133 reps if it all went to moving the weight. 

In reality, the body needs a lot of that energy to perform the arm, leg and back movements required for each rep. Some energy also gets lost to friction inside the muscles and the chemistry needed to make muscles contract, so the Whoppers can only put up a small fraction of those reps. But in our world of a perfect transition from candy to work, an Olympic weightlifter could do quite a bit with a box of Whoppers.

You Have the Power

LightbulbAnother concept related to energy we see daily is power, or the rate at which you expend energy. The metric unit of power is the Watt, which can also be written as Joules per second.

That means that multiplying Watts by an amount of time brings us back to energy. Multiplying by hours gives you Watt hours and by seconds brings you right back to Joules. Let’s see how many Tootsie rolls it takes to light a room.

Imagine you have a light fixture that takes three 60 Watt incandescent bulbs. The Wattage of a bulb represents how much power it takes to keep that bulb running, so each 60 Watt bulb requires 60 Joules of energy every second and the whole fixture requires 180 Joules per second.

Each Tootsie Roll Junior—the two-inch-long skinny ones—has 35 Calories, which when multiplied by 4,184, gives 146,440 Joules. If the fixture requires 180 Joules per second, then that Tootsie Roll will power the light for 813 seconds, just over 13.5 minutes. To keep that light running for eight hours, or 28,800 seconds, you would need 36 Tootsie Roll Juniors.

Lights aren’t the only things we could use our candy energy for. In the ultimate transition from irrelevant to eminently useful, we can use the energy from candy corn to charge a phone.

Most phone companies list battery capacity in terms of hours of use or how many hours worth of electrical current they can put out. With a little knowledge of the battery’s operating voltage, you can convert that current measurement into energy in the form of Watt hours.

The iPhone 7 has a battery capacity of 10.45 Wh. There are 3,600 Joules in a Watt hour so that iPhone 7 has 37,620 Joules in a fully charged battery. A Samsung Galaxy S6 has 9.81 Wh, which converts to 35,316 Joules. 

Each kernel of candy corn has 7.4 Calories, or 30,830 Joules, so with two kernels of candy corn you could get a full charge on your phone. 

Sadly, we cannot simply transfer candy energy into our daily lives. We will just have find another use for our leftover candy. Maybe arts and crafts. Maybe just eating it.

—Daniel Lane
Daniel Lane convers science, medicine, engineering and the environment in North Carolina.
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