A joule (J) is a small unit of energy. More commonly, we measure energy in kilojoules (kJ), which are units of a thousand joules each. A medium orange probably contains about 250kJ of chemical energy. The same weight of chocolates might contain 1700kJ of energy.
When we raise an apple up to a height of one meter, we perform approximately one joule of work. So what is a joule? Joule is the unit of energy used by the International Standard of Units (SI). It is defined as the amount of work done on a body by a one Newton force that moves the body over a distance of one meter. Wait a minute … is it a unit of energy or a unit of work?
Actually, it is a unit of both because the two are interrelated. Energy is just the ability of a body to do work. Conversely, work has done on a body changes the energy of the body. Let’s go back to the apple example mentioned earlier to elaborate. An apple is a favorite example to illustrate a one joule of work when using the definition given earlier (i.e., the amount of work done ….) because an apple weighs approximately one Newton. Thus, you’d have to exert a one Newton upward force to counteract its one Newton weight. Once you’ve lifted it up to a height of one meter, you would have performed one joule of work on it.
Now, how does energy fit into the picture? As you perform work on the apple, the energy of the apple (in this case, its potential energy) changes. At the top, the apple would have gained about one joule of potential energy. Also, when the apple is one meter above its original position, say the floor, gravity would have gained the ability to do work on it. This ability, when measured in joules, is equivalent to one joule.
Meaning, when you release the apple, the force of gravity, which is simply just the weight of the body and equivalent to one Newton, would be able to perform one joule of work on it when the apple drops down from a height of one meter.
Picture Credit : Google
