What is kinetic energy?

We explain what kinetic energy is. In addition, the difference between potential energy and kinetic energy, and some examples.

1. What is kinetic energy?

Kinetic energy is that energy that has a body or system due to its movement.

The physical defined as the amount of work needed to accelerate a body of mass determined and in the rest position, until reaching a certain speed. Once this point has been reached, according to the Law of inertia , the amount of accumulated kinetic energy will remain identical unless a change in speed occurs or the body returns to its resting state, after suffering a negative work of the same magnitude.

Kinetic energy is often represented by the symbol E _c (which may be E ₊ or E _– , depending on the case), although sometimes the symbols T or K are also used . It is usually expressed in Joules (J).

It is possible to determine the kinetic energy of an object using various formulas in classical mechanics , such as: E _c = (mv ² ) / 2 where m is the mass (Kg) of the object and v its velocity (m / s). Thus, 1 J = 1Kg. 1m ² / s ² .

However, being related to speed, in relativistic mechanics it will not only depend on the nature of the object, but also on its relationship with the observer and with the inertial reference system. In a Cartesian plane , the formula would be as follows: E _c = [m. (X ² + Y ² + Z ² )] / 2.

In any case, this energy can be understood as the energy that prints the movement on the object , and can easily be transformed into heat or other forms of energy.

2. Kinetic Energy Types

There are no proper types of kinetic energy, however each particular approach of physics presents its own perspective on it, for example:

• In classical mechanics . The kinetic energy is understood according to different reference systems, particle systems or rigid solids in rotation. Each of them represents a specific case with specific calculation formulas and variables to consider.
• In relativistic mechanics . The mechanics influenced by the Theory of relativity considers kinetic energy based on two scenarios: the kinetic energy of a particle and that of a solid in rotation.
• In quantum mechanics . The mechanics of atomic particles take into account kinetic energy based on quantum particles (smaller than an atom ) and rigid solids formed by infinite numbers of particles.

3. Difference between potential energy and kinetic energy

The kinetic energy (E _c ) and the potential energy (E _p ), added together, make up the mechanical energy (E _m ) of an object or system . However, they are distinguished in that while the first concerns the moving bodies, the second has to do with the amount of energy accumulated within an object at rest.

That said, the potential energy depends on how the object or system is positioned relative to the field of forces around it, while the kinetics has to do with the movements it undertakes.

There are three types of potential energy:

• Gravitational potential energy . Linked to the height at which the objects are and the attraction of gravity on their bodies.
• Elastic potential energy . It has to do with the tendency of certain objects to recover their original form, once they have been forced by an external force to abandon it.
• Electric potential energy . It refers to the amount of work contained in a given electric field, when an electric charge inside it goes from a point in the field to infinity.

4. Examples of kinetic energy

Some examples where the kinetic energy is verified can be:

• Throw a ball through the air . We print force on a ball to throw it into the air, letting it fall by gravity. In doing so, he will acquire a kinetic energy that, when another player stops him, he must compensate with a job of equal magnitude, if he wishes to stop it and retain it.
• A roller coaster car . A classic example: the roller coaster car of an amusement park will present a potential energy until the moment it starts to fall, and its speed and mass give it a growing kinetic energy. The latter will be greater if the car is full than if it is empty (as there is more mass).
• Knock someone down . If we run to a friend and throw ourselves on him, the kinetic energy we gain during the race will overcome the inertia of his body and we will knock him down. In the fall, both bodies will add the joint kinetic energy and it will finally be the ground that stops the movement.