Energy Sciences

Two Types of Energy

From the physics point of view, energy is the ability to do work and it occurs in the form of chemical energy, thermal energy, electromagnetic radiation, gravitational energy, electric energy, elastic energy, nuclear energy, and rest energy. The energy can be stored in different forms, for which it receives the name of potential energy, or it can be a property of an object in motion, obtaining in this case the name of "kinetic energy." It is said that these are the only types of energy. Any other type of energy would fall in one of the two categories already mentioned. In addition to this idea, we can encounter a combination of both types of energy. In other words, the addition of potential and kinetic energy would give us what we call "total energy."

Potential Energy

As an example of potential energy, we can have a brick at the border of a table as it is shown in figure 1. The distance of the brick to the ground will influence the amount of potential energy. The amount of mass of the brick will also make a difference. One can easily understand that it will not be the same to have a brick as to have a pencil. It is obvious that the pencil is less probable to cause any damage to the floor, but it cannot be said the same about the brick. This type of potential energy is also known as "gravitational potential energy" because the energy depends on the mass located within a gravitational field.

The formula used to calculate the "gravitational potential energy E _p" is: E _p = mgh. In this formula, m represents the mass of the object, g is the acceleration of gravity and h is the height of the brick. Similarly, potential energies can be found within a magnetic field, an electric field, in the wet and dry batteries or inclusive in a system with a compressed spring. In this last case, the potential energy is present as soon as the spring is compressed.

Kinetic Energy

Kinetic energy is the result of an object with mass "m" that is traveling at a certain speed "v." This situation is as well found in the movement of our muscles when the glucose is broken to produce the amount of energy needed to move our body. The flow of water through a tube, the power produced by the wind and electrons moving around the nucleus of an atom, are also examples of kinetic energy. The formula to calculate the kinetic energy is:

E _k = ½ m v ², where "m" is the mass and "v" is the speed of the object.

In the above formula for kinetic energy, the value of "v" is considered to be less than the speed of the light, which Albert Einstein used in his Relativity theory calculating the amount of energy as:

E = mc ² where c represents the speed of the light.

On the left side of figure-1, if the brick would be falling, the height at a certain moment would produce an amount of potential energy. To calculate the total energy, the potential energy would need to be added to the kinetic energy that would appear because the brick will be now in motion. This "total energy" is:

E = ½ m v ² + mgh.

A good example of where the total energy can be calculated is a roller coaster going down and in the middle of the hill as it is shown on the right side of figure-1.