Energy Measurement Units & Unit Conversion

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  • 0:01 What Is Energy?
  • 0:54 The Newton & Joule
  • 1:46 The Calorie
  • 2:34 Btus, Therms, & kWh
  • 4:28 Conversion Examples
  • 7:33 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

It's important to understand both how energy is measured and the different units used in those measurements. In this lesson, you'll learn about common energy measurement units, as well as see examples showing how to convert between them.

What Is Energy?

When you hear the term 'energy' what do you think of? Maybe the electricity that powers the appliances in your home, or the gas that powers your car to get you where you need to go. But, how about a group of kids that just ate a bunch of cookies? Or, the effort it takes you to lift weights at the gym?

All of these are associated with energy because energy is simply the ability to do work. But this also means that describing energy can be a bit complicated because you'll need to define what type of energy you're talking about, like thermal, chemical, or electrical, as well as make sure you use the appropriate unit of measure. There are a lot of different units that are used for energy measurement and probably just as many ways to convert between them. Let's go through some of the more common units that you should be familiar with and then work through some examples of how you would go from one unit to another.

The Newton and Joule

It's only fitting that we start with the unit named for the man who is considered the father of modern science, Sir Isaac Newton. The newton is the standard unit of force and is represented with the capital letter N. It's equal to 1 kg * m per s^2, which is about the amount of force needed to lift an apple over your head.

The joule, which is the amount of energy needed to lift a 1 N object over a 1 meter distance, is also named for a very important scientist, Sir James Prescott Joule. Like a newton, a joule (J) is a fairly small amount of energy. For example, a donut contains about 1-mega joule worth of energy, or 10^6 J. That's one million joules in just that one donut!

The Calorie

Another unit you could use to describe the energy in that donut, and one you're probably more familiar with, is the calorie (cal). This is the amount of heat needed to raise the temperature of 1 gram of water by 1°C. This is not the same as the Calorie (Cal), which is a kilocalorie, or 1,000 calories. Food calories are always kilocalories, or Calories (with a capital C). So, if that donut you just ate has 700 Calories, that means it actually has 700 kilocalories, or 700,000 calories (with a little c)! A calorie is also the same as 4.186 J, but we'll get into that in just a bit.

Btus, Therms, & kWh

If you own an air conditioner, water heater, or furnace, you're probably familiar with the energy unit Btu. This stands for British thermal unit and is the amount of heat needed to raise 1 pound of water by 1°F. A single Btu is yet another small amount of energy - similar to the amount of heat one match puts out. Therefore, your household appliances will be rated at large values, like 40,000 or 80,000 Btus. 1 Btu is also equal to 252 cal (with a little c), or 1,055 J.

Therms, or thermal units, are larger than Btus. In fact, 1 therm is 100,000 Btu, or about the amount of energy released from burning 100 cubic feet of natural gas. Finally, we have the kWh, which stands for kilowatt hour, and is the amount of energy used to produce 1 kilowatt of electricity for an hour. This is what you see on your electric bill, telling you how much energy you've used to power your house each month.

The watt is named for James Watt, who invented the steam engine and is the same as 1 J per second. Just like the kilocalorie is 1,000 calories, the kilowatt is 1,000 watts, which means that to get a kWh, we simply multiply 1,000 J per s * 3,600 s (there are 3,600 seconds in an hour), which is the same as 3.6 * 10^6 J (that's over 3 million J!). This is about how much it takes to power ten 100-watt light bulbs for one hour, which shows you just how small 1 J really is.

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