Physical bodies are what? Physical bodies: examples, properties

In today's article, we discuss what a physical body is. No doubt, this term has already met you many times during school years. With the concepts of "physical body," "substance," "phenomenon," we first encounter in the lessons of natural history. They are the subject of study of most sections of the special science - physics.

By definition, the term "physical body" refers to a specific material object that has a form and a clearly expressed outer boundary that separates it from the environment and other bodies. In addition, the physical body is characterized by such characteristics as mass and volume. These parameters are basic. But apart from them there are others. We are talking about transparency, density, elasticity, hardness, and so on.

Physical bodies: examples

Simply speaking, we can call any of the surrounding objects a physical body. The most common examples are a book, a table, a car, a ball, a cup. A simple body is called by a physicist whose geometric form is simple. Composite physical bodies are those that exist in the form of combinations of simple bodies fastened together. For example, a very conventional human figure can be represented as a collection of cylinders and balls.

The material from which any of the bodies consists is called matter. In this case, they can contain in their composition both one and a number of substances. Let us give some examples. Physical bodies - cutlery (forks, spoons). They are made of steel most often. The knife can serve as an example of a body consisting of two different kinds of substances - a steel blade and a wooden handle. And such a complex product, like a cell phone, is made from a much larger number of "ingredients."

What are the substances

They can be natural and created artificially. In ancient times, people made all necessary items from natural materials (arrowheads - from stones, warm clothes - from animal skins). With the development of technological progress, substances created by man appeared. And at the moment there are a majority. A classic example of a physical body of artificial origin is plastic. Each of its kind was created by the person with the purpose of maintenance of necessary qualities of this or that subject. For example, transparent plastic - for lenses glasses, non-toxic food - for dishes, durable - for car bumper.

Any object (from a stone ax to a high-tech device) has a number of specific qualities. One of the properties of physical bodies is their ability to be attracted to each other as a result of gravitational interaction. It is measured by means of a physical quantity called the mass. According to the definition of physicists, the mass of bodies is a measure of their gravity. It is denoted by the symbol m.

Measurement of mass

This physical quantity, like any other, is measurable. To find out what is the mass of any object, you need to compare it with the standard. That is, with a body whose mass is taken as one. The international system of units (SI) is a kilogram. Such an "ideal" unit of mass exists in the form of a cylinder, which is an alloy of iridium and platinum. This international model is stored in France, and copies of it are available in almost every country.

In addition to a kilogram, use the notion of a ton, gram or milligram. Measure the same body weight by weighing. This is a classic way for everyday calculations. But in modern physics there are other methods of measurement, much more modern and highly accurate. With their help determine the mass of microparticles, as well as giant objects.

Other properties of physical bodies

Form, mass and volume are the most important characteristics. But there are other properties of physical bodies, each of which is important in a certain situation. For example, objects of equal volume can differ significantly in their mass, that is, have different density. In many situations, such characteristics as fragility, hardness, elasticity or magnetic qualities are important. Do not forget about the thermal conductivity, transparency, homogeneity, electrical conductivity and other numerous physical properties of bodies and substances.

In most cases, all such characteristics depend on the substances or materials from which the objects consist. For example, rubber, glass and steel balls will have absolutely different sets of physical qualities. This is important in situations of interaction of bodies with each other, for example, studying the degree of deformation of them during collision.

On the approximations adopted

Certain physical branches of physics are regarded as a kind of abstraction with ideal characteristics. For example, in mechanics, the bodies are represented in the form of material points that do not have mass or other properties. This section of physics deals with the movement of such conditional points, and to solve the problems posed here, such quantities are of no fundamental importance.

In scientific calculations, the concept of an absolutely rigid body is often used. Such conditionally it is considered not subject to any deformations, with absence of displacement of the center of mass a body. This simplified model allows to theoretically reproduce a number of certain processes.

The section of thermodynamics uses the concept of an absolutely black body for its own purposes. What is it? A physical body (an abstract object), capable of absorbing any radiation incident on its surface. At the same time, if the problem requires it, electromagnetic waves can be emitted to it. If, according to the conditions of theoretical calculations, the shape of physical bodies is not fundamental, by default it is considered that it is spherical.

Why the properties of bodies are so important

Physics itself as such arose from the need to comprehend the laws by which physical bodies behave, as well as the mechanisms of the existence of various external phenomena. To natural factors it is possible to attribute any changes in our environment, not related to the results of human activity. Many of them use people to their advantage, but others can be dangerous and even catastrophic.

The study of the behavior and the most diverse properties of physical bodies is necessary for people in order to predict the adverse factors and prevent or reduce the damage they cause. For example, the construction of breakwaters people are used to combat the negative manifestations of the sea elements. To resist earthquakes, mankind has learned how to develop special earthquake-proof structures of buildings. Bearing parts of the car are made in a special, carefully verified form to reduce damage during accidents.

On the structure of bodies

According to another definition, the term "physical body" means everything that can be recognized as real. Any of them necessarily occupies a part of space, and the substances from which they are composed are a collection of molecules of a certain structure. Other, smaller particles of it are atoms, but each of them is not something indivisible and completely simple. The structure of the atom is quite complicated. In its composition, it is possible to distinguish positively and negatively charged elementary particles-ions.

The structure according to which such particles are aligned in a certain system, for solid bodies is called crystalline. Any crystal has a definite, strictly fixed form, which indicates the ordered motion and interaction of its molecules and atoms. When the structure of crystals changes, the physical properties of the body are disturbed. The degree of mobility of elementary constituents depends on its aggregate state, which can be solid, liquid or gaseous.

To characterize these complex phenomena, the notion of compression coefficients or bulk elasticity, which are mutually inverse quantities, is used.

Motion of molecules

The state of rest is neither inherent in atoms nor in molecules of solids. They are in constant motion, the nature of which depends on the thermal state of the body, and the effects that it is currently undergoing. Part of the elementary particles - negatively charged ions (called electrons) moves at a higher speed than those having a positive charge.

From the point of view of the aggregate state, physical bodies are solid objects, liquids or gases, which depends on the nature of the molecular motion. The whole set of solids can be divided into crystalline and amorphous. The motion of the particles in the crystal is completely ordered. In liquids, molecules move along a completely different principle. They move from one group to another, which can be figuratively represented like the comets that wander from one heavenly system to another.

In any of the gaseous bodies, the molecules have a much weaker bond than in the liquid or solid. Particles there can be called repulsive from each other. The elasticity of physical bodies is determined by a combination of two main quantities - the shear coefficient and the coefficient of bulk elasticity.

Fluidity of bodies

For all the significant differences between solid and liquid physical bodies, there are many similarities in their properties. Some of them, referred to as soft, occupy an intermediate aggregate state between the first and second with inherent both of these physical properties. This quality, like fluidity, can be found in a solid body (example - ice or shoemaker var). It is inherent in metals, including hard ones. Under pressure, most of them can flow like a liquid. By combining and heating two solid pieces of metal, it is possible to weld them together into a single whole. Moreover, the soldering process proceeds at a temperature much lower than the melting point of each of them.

This process is possible provided that both parts are in full contact. In this way, various metal alloys are produced. The corresponding property is called diffusion.

About liquids and gases

According to the results of numerous experiments, scientists came to the following conclusion: solid physical bodies are not some isolated group. The difference between them and the liquid consists only in greater internal friction. The transition of substances to different states occurs under conditions of a certain temperature.

Gases are different from liquids and solids in that the increase in the elastic force does not occur even with a strong change in volume. The difference between liquids and solids is in the appearance of elastic forces in solids under shear, that is, a change in shape. This phenomenon is not observed in liquids that can take any of the forms.

Crystalline and amorphous

As already mentioned, two possible states of solids are amorphous and crystalline. Amorphous include bodies that have the same physical properties in all directions. This quality is called isotropy. As an example, you can cure hardened resin, products from amber, glass. Their isotropy is the result of the disorderly arrangement of molecules and atoms in the composition of matter.

In the crystalline state, the elementary particles are arranged in a strict order and exist as an internal structure periodically repeating in different directions. The physical properties of such bodies are different, but in parallel directions they coincide. This property inherent in crystals is called anisotropy. Its cause is the unequal force of interaction between molecules and atoms in different directions.

Mono- and polycrystals

In single crystals, the internal structure is homogeneous and is repeated throughout the volume. Polycrystals look like a lot of small crystals crystallizing together randomly. The constituent particles are located at a strictly defined distance from each other and in the desired order. A crystal lattice is understood to mean a set of nodes, that is, points serving as centers of molecules or atoms. Metals with a crystal structure serve as a material for the skeletons of bridges, buildings and other sturdy structures. That is why the properties of crystalline bodies are carefully studied for practical purposes.

The actual strength characteristics are adversely affected by defects in the crystal lattice, both surface and internal. A separate section of physics, called solid-state mechanics, is devoted to similar properties of solids.