Energy is one of the most fundamental parts of our universe. We use energy to do work. Energy lights our cities. Energy powers our vehicles, trains, planes and rockets. Energy warms our homes, cooks our food, plays our music, gives us pictures on television. Energy powers machinery in factories. Energy is defined as "the ability to do work." When we eat, our bodies transform food into energy that allows us to do work. When we run or walk, we "burn" food energy in our bodies. When we think or read or write, we are also doing work. Cars, planes, trollies, boats and machinery also transform energy into work. Work means moving something over a distance. In order for something to work, energy is necessary. Nothing works unless energy is present. But where does energy come from and how is it measured? Our energy on earth ultimately comes from the sun. Think about it, would life exist without the sun? Unfortunately, we have a problem with the sun's energy. It's in a form we cannot use. Luckily we have something on earth that can convert the sun's energy into a usable form ... plants. There are many forms of energy, and plants can convert the sun's energy into one of these forms - chemical energy. Chemical energy is the energy necessary to hold molecules together. Water consists of two Hydrogen atoms and one Oxygen atom. What holds these atoms together? Energy known as chemical energy. Another form of energy is mechanical energy. Mechanical energy is associated with motion. Think of moving water, can flowing water do work for us. Think about the production of electricity ... a magnet must spin in the presence of a coil of wire; or a force must be applied over a distance. Look at the diagram below and imagine how water applies that force of a distance for us.

An object that is moving can do work on another object, and thus has energy. Does energy always have to be in motion? No, sometimes energy can be at rest. Think of a gas tank. Inside the tank is gasoline (or chemical energy). If the car is not cranked, the chemical energy of the gasoline is at rest. Quite simply, it's at rest. Energy at rest is called potential energy. Once the car is cranked the chemical energy of the gasoline is converted into the mechanical energy of the moving pistons in the engine. The energy is set into motion, the pistons move up and down - force is applied over a distance. Energy in motion is called kinetic energy. In the example I just gave, notice how potential energy was converted to kinetic energy. Energy conversions take place similarly. Think of a pendulum swing back and forth. Kinetic energy being converted potential over and over. A continuous conversion between kinetic and potential energy takes place. Potential energy is greatest at the two highest points in the swing and zero at the bottom. Where is kinetic energy greatest? Look at the roller coaster picture below, the coaster is a good example as to how kinetic energy and potential energy are being converted from one to the other.

All forms of energy can be converted to other forms. Mechanical can be converted into electrical, electrical to heat, etc. Antoine Lavoisier in 1785 stated the Law of Conservation of Mass, which says mass cannot be created or destroyed. In 1842, Julius Robert Mayer discovered the Law of Conservation of Energy, which states energy cannot be created or destroyed. So then what becomes of mass and energy? Basically, mass and energy can be converted from one form to another. In 1905 Albert Einstein gave us the formula e=mc². What he explained to us was that if mass is destroyed energy is created, and if energy is destroyed mass is created. One can be converted into the other. The total amount of mass and energy is conserved.

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