Kinetic energy and potential energy explained.

Energy

Energy exists in two distinct forms: potential and kinetic, potential energy is stored-up energy. It is the result of work having been done. When you wind up a clock you do a certain amount of work in overcoming the resistance of the spring and winding the key through a certain total distance.

 When you ride to the top of a tall building the elevator, in lifting you that distance, does a certain amount of work on your body. In taking you up the elevator stored up potential energy in you as well as in itself, and when you leave it, the total potential energy decreases by your potential energy. Your body, then, has potential energy.

We may say then that whenever one body does work upon another body, energy is transformed from the body that does the work to the body that has the work done to it. We shall see when we consider the subject of heat, that heat is another form of energy. Heat produces energy and then energy makes heat. Heat makes steam which runs the steam engine, and heat is produced in the wheel when the brakes are applied to stop the train.

Energy is continually being transformed from one form to another. Potential energy turns into kinetic energy and kinetic energy turns into potential energy. A baseball thrown vertically up into the air is continuously transforming its kinetic energy into potential energy. When the kinetic energy is at a minimum and the potential energy is at a maximum, the ball stops for a split second. This is its highest point and from then on it falls, and by so doing transforms its potential energy back into kinetic energy.

Whenever one form of energy disappears, another form appears in an equivalent amount, so that, the total amount of Energy in the entire universe is always the same. This is one of the most important laws in physics and is known as the law of Conservation of energy. It states that energy can be put into a machine you must get out of it. That is why something for nothing no matter how you try. 

Of course, a certain amount of energy is made unavailable because it is transformed into heat, due to the friction of the machine, and this heat radiates into outer space. But that is another form of energy, capable of being transformed, so the heat due to friction in the machine is merely another form of the same thing.