What is kinetic energy?
In the field of physics, kinetic energy is the energy associated with bodies in motion, and it represents the force that allows an object to move from a state of rest to a state of movement at a specific speed.
When an object is at rest, its kinetic energy is zero. The moment an accelerating force acts on it and it is set in motion, its kinetic energy increases proportionally. In order for the body to return to its initial state of rest, it must receive the same magnitude of energy it has invested to start moving, but in an opposite or negative way.
According to the Law of Inertia, the first of Newton’s Laws, once a certain speed is reached, the amount of kinetic energy will remain constant unless another force acts on the object to change its velocity and, thus, its kinetic energy.
In conclusion, this type of energy refers to the work required to accelerate a body from an initial point of rest to a certain speed.
What are the types of kinetic energy?
Kinetic energy is classified into two types, according to the movement:
- Translational kinetic energy: describes the trajectory of the body itself, such as the movement of a car on a road.
- Rotational kinetic energy: describes the movement of the object construction skeleton, such as a car tire.
How is kinetic energy calculated?
According to the international system of units, kinetic energy is measured in Joules, and it is expressed with the letter J. To calculate it, two fundamental elements must be taken into account: the mass of the body, expressed with the letter m and the velocity of movement, expressed with the letter v.
Considering these concepts, calculating kinetic energy (Ek) is done with the following mathematical formula: Ek = (½)m * v2; this means that the kinetic energy is proportional to half the mass of the body multiplied by the square of the velocity of movement. This means that the greater the mass of the body, as well as the speed with which it moves, the greater the force needed to generate kinetic energy.
However, kinetic energy can be measured in different ways depending on the characteristics of the body. Depending on its mass and velocity, the kinetic energy can be calculated according to the rules of:
- Classical mechanics: when the kinetic energy depends on the mass and velocity of the body, and the latter is less than the speed of light.
- Relativistic mechanics: it is calculated knowing that the speed of the body is close to the speed of light, so the kinetic energy depends on the relationship between both speeds.
- Quantum mechanics: subatomic particles are involved, so the physical magnitudes (i.e. the body) are described with wave functions.
What is the difference between kinetic energy and potential energy?
The mechanical energy of an object consists of kinetic energy and potential energy. The difference between these two types of energy is that the first corresponds to moving objects, while the second refers to the energy stored in an object at rest.
Therefore, depending on how an object is located with respect to the field of forces around it, it will use potential energy; depending on the movements it performs, it will use kinetic energy.
In what everyday circumstances is kinetic energy used?
Since kinetic energy manifests itself in every moving body, it is constantly present in our daily lives. For example:
- Moving vehicles use kinetic energy to move since they are made of mass and travel at a certain speed. By using the mathematical formula, it can be deduced that a truck moving along a highway at a certain speed will have more kinetic energy than a car due to its size.
- The movement of the propellers to get hydraulic or electric power via the flow of water happens thanks to kinetic energy.
- Airplanes use a high amount of kinetic energy due to their large size and the speed with which they move. This energy is what enables them to fly so high.