Introduction: Energy causes things to happen around us. Look out 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 drivers 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.
We learned the definition of energy in the introduction.
"Energy Is the Ability to Do Work."
Energy can be found in a number of different forms. It can be chemical energy, electrical energy, heat (thermal energy), light (radiant energy), mechanical energy, and nuclear energy.
Stored and Moving Energy
Energy makes everything happen and can be divided into two types:
- Stored energy is called potential energy.
- Moving energy is called kinetic energy.
With a pencil, try this example to know the two types of energy.
Put the pencil at the edge of the desk and push it off to the floor. The moving pencil uses kinetic energy.
Now, pick up the pencil and put it back on the desk. You used your own energy to lift and move the pencil. Moving it higher than the floor adds energy to it. As it rests on the desk, the pencil has potential energy. The higher it is, the further it could fall. That means the pencil has more potential energy.
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.