The subject of study in many branches of physics is the behavior of physical bodies, their properties and features of interaction with each other.
However, before starting to study them, it is necessary to determine what the physical body is and what characteristics it possesses.
Physical body – definition
In physics, speaking of a physical body, they mean a certain material object that has a form defined by an external boundary that separates it from other bodies and the external environment, as well as a volume and mass corresponding to this form.
In addition to the above basic characteristics, a physical body can have a number of other properties – density, transparency, hardness / elasticity, etc. All objects that surround us are physical bodies. A cup, a desk, a ball, a book, a truck – they are all physical bodies from the point of view of physics.
Physicists distinguish between simple bodies, which have a simple geometric shape, and composite bodies, which are combinations of simple bodies fastened together. Such a representation is necessary to simplify calculations, especially in cases where the internal state of the physical body does not play a large role in the process under study. For example, the human body can be viewed as a collection of balls and cylinders.
Properties of physical bodies
In addition to shape, volume and mass, physical bodies are characterized by a number of other properties that can be important in various situations. So, bodies of the same volume often differ in mass and, accordingly, in density. In addition, in a number of cases, other characteristics of bodies are also important – their hardness, fragility, elasticity, magnetic properties, transparency, thermal conductivity, homogeneity, electrical conductivity, etc. To a large extent, these properties depend on the materials that make up the physical bodies.
So, balls made of rubber, concrete, wool, glass and steel will have completely different sets of physical properties. However, their properties will be important only in the case when the interaction of bodies with each other is investigated – for example, it is necessary to find out the degree of deformation of certain bodies in a collision.
Absolutely solid body, material point and other abstractions
In some sections of physics, bodies are considered not in the aggregate of their inherent properties, but as some abstractions that are assigned ideal characteristics. So in mechanics, all bodies are represented as material points, without taking into account their mass and other physical properties. This discipline studies the movement of material points without taking into account their real size and mass, since these quantities are not important for solving a number of problems. If you are calculating the average speed of a train over a certain distance, you do not need to know how many carriages there are on the train.
Often physicists use the concept of an absolutely rigid body to perform any calculations. It never undergoes deformation, its center of mass does not shift, which makes it possible to simulate a number of processes without unnecessary complication. To solve thermodynamic problems, it is convenient to use an absolutely black body – an abstract object that absorbs all radiation falling on its surface.
In this case, the body itself can emit electromagnetic waves, if required by the task at hand. In cases where the shape of the physical body does not matter, it is assumed that it has the shape of a ball.
Physical body and physical phenomenon
Physics as a science arose from the need to identify the laws of behavior of physical bodies and the mechanisms of formation of natural phenomena. In fact, all changes in our environment that are not related to human activities are natural phenomena. Most of them are useful to people, but there are also dangerous and even catastrophic natural phenomena.
People need to study the properties and behavior of physical bodies that take part in them in order to learn how to predict adverse events, prevent them or reduce the harm they cause. So, the harmful effect of sea waves has long been learned to reduce by building breakwaters – concrete ledges entering the sea for tens of meters and breaking a single wave front.
The destructive effect of earthquakes is overcome by the construction of seismic resistant buildings of a special design. To reduce damage when the vehicle comes into contact with solid objects, the supporting structures of its body are given a special shape. All this became possible thanks to the study of the characteristics of physical bodies.