The body is one of the basic concepts in the physicist who is meant as a form of existence of matter or substance. It is a material object which is characterized by the volume and weight, sometimes also other parameters. The physical body is obviously separated from other bodies by border. There are several special types of physical bodies, it is not necessary to understand their transfer as classification.
In mechanics the physical body most often is understood as a material point. It is a certain abstraction which main property is the fact that the actual sizes of a body for the solution of a specific objective can be neglected. In other words, the material point is quite concrete physical body which has the sizes, the form and other similar characteristics, but they are not important at all to solve the available problem. For example, if it is necessary to count the average speed of an object on a certain site of a way, at the solution of a task it is possible not to reckon with its length at all. One more type of physical bodies considered by mechanics is a rigid body. The mechanics of such body just the same, as well as mechanics of a material point, but in addition has also other properties. The rigid body consists of material points, but neither distance between them, nor distribution of weight do not change under loadings to which the body is exposed. It means that it cannot be deformed. To define the provision of a rigid body, it is enough to set the system of coordinates tied to it, usually Cartesian. In most cases the center of weight is as well the center of a system of coordinates. In the nature of a rigid body does not exist, but such abstraction is very convenient for the solution of many tasks though in relativistic mechanics it is not considered as at movements which speed is comparable at the speed of light this model shows internal contradictions. Contrast to a rigid body is the deformable body which particles can be displaced from each other. There are special types of physical bodies and in other branches of physics. For example, in thermodynamics the concept of absolutely black body is entered. It is ideal model, such physical body which absorbs all electromagnetic radiation getting on it. At the same time, it can quite produce electromagnetic radiation and have any color. An example of an object which is brought most closer on properties to absolutely black body it is the Sun. If to take the substances spread for Earth, then it is possible to remember soot which absorbs 99% of the radiation getting on it except infrared with which absorption this substance copes much worse.