Energy causes things to happen around us. Look out of the window. During the day, the sun gives out light and heat energy. At night, street lamps use electrical energy to light our way. When a car drives by, it is being powered by gasoline, a type of stored energy. The food we eat contains energy. We use that energy to work and play.
"Energy Is the Ability to Do Work."
How Do We Measure Energy?
Energy is measured in many ways.
One of the basic measuring blocks is called a Btu. This stands for British thermal unit and was invented by, of course, the English.
Btu is the amount of heat energy it takes to raise the temperature of one pound of water by one degree Fahrenheit, at sea level.
One Btu equals about one blue-tip kitchen match.
One thousand Btus roughly equals: One average candy bar or 4/5 of a peanut butter and jelly sandwich.
It takes about 2,000 Btus to make a pot of coffee.
Energy also can be measured in joules. Joules sounds exactly like the word jewels, as in diamonds and emeralds. A thousand joules is equal to a British thermal unit.
1,000 joules = 1 Btu
So, it would take 2 million joules to make a pot of coffee.
The term "joule" is named after an English scientist James Prescott Joule who lived from 1818 to 1889. He discovered that heat is a type of energy.
One joule is the amount of energy needed to lift something weighing one pound to a height of nine inches. So, if you lifted a five-pound sack of sugar from the floor to the top of a counter (27 inches), you would use about 15 joules of energy.
Around the world, scientists measure energy in joules rather than Btus. It's much like people around the world using the metric system of meters and kilograms, instead of the English system of feet and pounds.
Like in the metric system, you can have kilojoules — "kilo" means 1,000.
1,000 joules = 1 kilojoule = 1 Btu
A piece of buttered toast contains about 315 kilojoules (315,000 joules) of energy. With that energy you could:
Jog for 6 minutes
Bicycle for 10 minutes
Walk briskly for 15 minutes
Sleep for 1-1/2 hours
Run a car for 7 seconds at 80 kilometers per hour (about 50 miles per hour)
Light a 60-watt light bulb for 1-1/2 hours
Or lift that sack of sugar from the floor to the counter 21,000 times!