Kinetic energy is, by 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 of modern mechanics. In short, this is the energy of motion, or the difference between the total energy and the rest energy. Nevertheless, its essence is not fully considered in modern science.
Kinetic energy (from gr. Kinema - movement) of a body in a state
immobility is zero. Often this value is associated not only with mass and speed. So, according to one definition, kinetic energy is 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 motion and in 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 a body is represented as the sum of the kinetic energies of each of the elementary volumes of a given body. Or as the value of the moment of inertia multiplied by the square of the angular velocity divided by two.
Suppose there is some solid body that moves around an axis
motionless passing through it. This object can be divided into small elementary volumes, each of which has its own elementary mass. Around the fixed axis, the body under consideration makes movements. In addition, each of the elementary volumes describes a circle of a corresponding radius. The
angular velocity 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 ones moving around the axis of volumes. 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 sliding without sliding along an inclined line. Moving forward, he performs a translational motion, however, while he 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 weight, as well as on its distribution with respect to the axis of rotation. What is it? This is a measure of the inertia of movement around the axis, just as in translational motion, the measure of inertia is mass. This is a very important quantity. The greater the moment of inertia, the more difficult it is 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 is rad / s. Angular velocity is the ratio of the angle of rotation to the period of time during which this angle passes a rotating object.
The kinetic energy theorem can be formulated approximately like this: the work of the force acting as a resultant applied to a certain body is equivalent to a change in the kinetic energy of a given body.