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Physics: What is Energy?

Updated on February 28, 2013
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What is energy? Energy surrounds us and is integral to everything we do and everything that happens. Energy is necessary to make things happen.

Forms of Energy

There are two main types of energy: kinetic energy and potential. Kinetic energy is the energy of motion. For example, a ball that has been thrown and is flying through the air exhibits kinetic energy. Potential energy is a passive form of energy. It is essentially stored energy. For example, a rock perched on a cliff has potential energy because it may, at any moment, become loose and fall off the cliff.

Kinetic and potential energy demonstrate the principle that energy is transferred from one object to another. The ball, before it had kinetic energy, had potential energy as a stationary object. When someone picked it up to throw it, energy was transferred to the ball to place it in motion. One of the main principles of energy is that it is never created nor destroyed, but that it is passed from one object to another.

Forms of Potential and Kinetic Energy

It is important to note that there are many types of energy that can be classified as potential energy, kinetic energy, or some combination of the two.

· Thermal energy. Thermal energy is actually a combination of kinetic and potential energy. Imagine a bathtub full of hot bathwater. It is not in motion, exhibiting potential energy, but the molecules of water are moving and bumping into one another, exhibiting kinetic energy.

· Chemical energy. Chemical energy can be either potential energy or kinetic energy. For example, a banana that you eat has energy stored inside. When you eat it, chemical processes in the body convert it to chemical energy which your body uses to keep itself going.

· Light (electromagnetic) energy. Light or electromagnetic energy is basically energy that comes from the sun or any other light source.

· Electrical energy. Electric energy is basically energy that results from the movement of charged particles. A good example of electrical energy is when power companies burn fuel to make electrical energy for your home.

· Electrochemical energy. Electrochemical energy is a type of stored (potential) energy that can be converted into electrical energy. Batteries are a good example of electrochemical energy.

· Nuclear energy. Nuclear energy is the energy formed by the combining of atoms (fusion) or the splitting apart of atoms (fission).

Properties of Energy

As mentioned before, energy can be transferred from one object to another. And, energy is always conserved; it cannot be created nor destroyed. (This is known as the First Law of Thermodynamics.) Thirdly, energy exists in many forms. And, energy can be converted from one form of energy to another and vice versa. (This is known as the Second Law of Thermodynamics.

These are the key properties at the core of thermodynamics, the study of heat and its relationship to other forms of energy and work. There are basically two processes of energy conversion: reversible processes and irreversible processes. Reversible processes are those through which energy is converted from one form to another and back again. Irreversible processes are those that cannot be reversed. Energy is converted to an unusable form that cannot be converted back to its original form.


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