Kinetic energy is, according to the definition, a value equal to half the mass of a moving body, multiplied by the square of the speed of this body. This is one of the most important terms in modern mechanics. In short, it is the energy of motion, or the difference between the total energy and the rest energy. Yet its essence is not fully considered in modern science.
Kinetic energy (from Gr. Kinema - movement) of a body in the state of
immobility is zero. Often this value is associated not only with mass and speed. So, according to one definition, kinetic energy is the work done at a certain speed. Measured in joules.
The kinetic energy of a system is a quantity that is closely related to the speed of each of its points.
It is considered both in translational and rotational motion. The first case has already been explained in detail above, this is half the mass of an object multiplied by its speed squared. And the kinetic energy of rotation of the body is represented as the sum of the kineticenergies of each of the elementary volumes of the given body. Or as the value of the moment of inertia multiplied by the square of the angular velocity divided by two.
Let's say there is some rigid body that moves around an axis
fixed passing through it. This object can be divided into small elementary volumes, each of which has its own elementary mass. The body in question moves around a fixed axis. In this case, each of the elementary volumes describes a circle of the corresponding radius. The angular speed of their rotation is the same. And therefore the kinetic energy of a given body is the sum of the kinetic energies of all its elementary volumes moving around the axis. A simplified version of this formula is half the product of the square of the angular velocity and the moment of inertia.
In some cases, kinetic energy is the sum of both translational and rotational energy. For example, a cylinder rolling without slipping along an inclined line. Moving forward, it performs a forward movement, however, it also moves around its axis.
One of the components of the kinetic energy of rotation is the moment of inertia, which was mentioned above. It depends on the total body mass, as well as on its distribution with respect to the axis of rotation. What is it? This is a measure of the inertia of motion around an axis, just as in translational motion the measure of inertia is mass. This is a very important value. The greater the moment of inertia, theit is more difficult to bring the body into a state of rotation. Angular velocity characterizes the speed with which a rigid body moves around its axis. The unit of measure is rad/s. Angular velocity is the ratio of the angle of rotation to the time interval for which this angle passes a rotating object.
The kinetic energy theorem can be formulated something like this: the work of the resultant force applied to a certain body is equivalent to a change in the kinetic energy of this body.
