Solids are crystalline and amorphous bodies. Crystal is what ice was called in ancient times. And then they began to call quartz a crystal and considered these minerals to be petrified ice. Crystals are natural and are used in the jewelry industry, optics, radio engineering and electronics, as supports for elements in ultra-precision instruments, as an ultra-hard abrasive material.
Crystalline bodies are characterized by hardness and have a strictly regular position in space of molecules, ions or atoms, resulting in the formation of a three-dimensional periodic crystal lattice (structure). Outwardly, this is expressed by a certain symmetry of the shape of a solid body and its certain physical properties. In their external form, crystalline bodies reflect the symmetry inherent in the internal “packing” of particles. This determines the equality of the angles between the faces of all crystals consisting of the same substance.
In them, the distances from center to center between neighboring atoms will also be equal (if they are located on the same straight line, then this distance will be the same along the entire length of the line). But for atoms lying on a straight line with a different direction, the distance between the centers of the atoms will be different. This circumstance explains the anisotropy. Anisotropy is the main difference between crystalline bodies and amorphous ones.
More than 90% of solids can be classified as crystals. In nature they exist in the form of single crystals and polycrystals. Monocrystals are single crystals, the faces of which are represented by regular polygons; They are characterized by the presence of a continuous crystal lattice and anisotropy of physical properties.
Polycrystals are bodies consisting of many small crystals, “grown together” somewhat chaotically. Polycrystals are metals, sugar, stones, sand. In such bodies (for example, a fragment of a metal), anisotropy usually does not appear due to the random arrangement of elements, although anisotropy is characteristic of an individual crystal of this body.
Other properties of crystalline bodies: strictly defined temperature (presence of critical points), strength, elasticity, electrical conductivity, magnetic conductivity, thermal conductivity.
Amorphous - having no shape. This is how this word is literally translated from Greek. Amorphous bodies are created by nature. For example, amber, wax. Humans are involved in the creation of artificial amorphous bodies - glass and resins (artificial), paraffin, plastics (polymers), rosin, naphthalene, var. do not have due to the chaotic arrangement of molecules (atoms, ions) in the structure of the body. Therefore, for any amorphous body they are isotropic - the same in all directions. For amorphous bodies there is no critical melting point; they gradually soften when heated and turn into viscous liquids. Amorphous bodies are assigned an intermediate (transitional) position between liquids and crystalline bodies: at low temperatures they harden and become elastic, in addition, they can split into shapeless pieces upon impact. At high temperatures, these same elements exhibit plasticity, becoming viscous liquids.
Now you know what crystalline bodies are!
Solids are divided into amorphous and crystalline, depending on their molecular structure and physical properties.
Unlike crystals, the molecules and atoms of amorphous solids do not form a lattice, and the distance between them fluctuates within a certain range of possible distances. In other words, in crystals, atoms or molecules are mutually arranged in such a way that the formed structure can be repeated throughout the entire volume of the body, which is called long-range order. In the case of amorphous bodies, the structure of molecules is preserved only relative to each one such molecule, a pattern is observed in the distribution of only neighboring molecules - short-range order. An illustrative example is presented below.
Amorphous bodies include glass and other substances in a glassy state, rosin, resins, amber, sealing wax, bitumen, wax, and organic matter: rubber, leather, cellulose, polyethylene, etc.
Properties of amorphous bodies
The structural features of amorphous solids give them individual properties:
- Weak fluidity is one of the most well-known properties of such bodies. An example would be glass drips that have been sitting in a window frame for a long time.
- Amorphous solids do not have a specific melting point, since the transition to a liquid state during heating occurs gradually, through softening of the body. For this reason, the so-called softening temperature range is applied to such bodies.
- Due to their structure, such bodies are isotropic, that is, their physical properties do not depend on the choice of direction.
- A substance in an amorphous state has greater internal energy than in a crystalline state. For this reason, amorphous bodies are able to independently transform into a crystalline state. This phenomenon can be observed as a result of glass becoming cloudy over time.
Glassy state
In nature, there are liquids that are practically impossible to transform into a crystalline state by cooling, since the complexity of the molecules of these substances does not allow them to form a regular crystal lattice. Such liquids include molecules of some organic polymers.
However, with the help of deep and rapid cooling, almost any substance can transform into a glassy state. This is an amorphous state that does not have a clear crystal lattice, but can partially crystallize on the scale of small clusters. This state of matter is metastable, that is, it persists under certain required thermodynamic conditions.
Using cooling technology at a certain speed, the substance will not have time to crystallize and will be converted into glass. That is, the higher the cooling rate of the material, the less likely it is to crystallize. For example, to produce metal glasses, a cooling rate of 100,000 - 1,000,000 Kelvin per second will be required.
In nature, the substance exists in a glassy state and arises from liquid volcanic magma, which, interacting with cold water or air, quickly cools. In this case, the substance is called volcanic glass. You can also observe glass formed as a result of the melting of a falling meteorite interacting with the atmosphere - meteorite glass or moldavite.
Often solids are bodies that retain their shape and volume. However, from a physical point of view, it can be difficult to distinguish between the solid and liquid states of a substance using these characteristics.
A special class of substances, which in appearance can also resemble solids, are polymers.
Polymers (from the Greek polymeres - consisting of many parts, from poly - many and meros - share, part) are compounds with high molecular weight, the molecules of which consist of a large number of regularly and irregularly repeating identical or different units.
Natural polymers include natural rubber, cellulose, proteins, and natural resins. Examples of synthetic polymers are polystyrene, polyethylene, and polyesters.
Truly solids - these are crystals, one of the characteristic features of which is correctness of their appearance.
One can only marvel at the perfection of the shape of snowflakes and admire their beauty.
If saturated solution hyposulfite, a substance used in photography to fix images, is left in an open bath for several days, then large crystals, also of a fairly regular shape, form at its bottom.
Crystals of table salt and sugar also have the correct shape.
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The natural shape of crystals is polyhedra with flat faces and angles between them that are constant for each substance.
The shape of crystals of different substances is not the same. But crystals of the same substance can be of different colors. For example, quartz crystals are colorless, golden, pink, and pale lilac. Depending on the color, they are given different names. Quartz crystals, for example, may be called rock crystal, smoky rock crystal, or amethyst. From a jeweler's point of view, many crystals of the same substance can differ in fundamental ways. From the point of view of a physicist, there may be no difference between them at all, since the overwhelming majority of the properties of multi-colored crystals of the same substance are the same.
The physical properties of a crystal are determined not by its color, but by its internal structure. A very clear illustration of this statement is the difference in many properties of diamond and graphite, which have the same chemical composition.
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Single crystals are called single crystals . Some substances, such as rock crystal, can form very large single crystals, sometimes with very regular shapes.
A feature of many single crystals is anisotropy – difference in physical properties in different directions.
The anisotropy of crystals is closely related to their symmetry. The lower the symmetry of the crystal, the more pronounced the anisotropy.
Let's take two plates cut from a quartz crystal in different planes. Let's drop wax onto the plates and let it harden, after which we touch the resulting wax spots with a hot needle. Based on the shape of the melted wax, we can conclude that a plate cut from a crystal in a vertical plane has different thermal conductivity in different directions.
If you cut two identical bars from a large piece of ice in mutually perpendicular directions, place them on two supports and load them, then the bars will behave differently. One block will slowly bend as the load increases. The other will retain its shape up to a certain load value and then break.
In a similar way, we can talk not only about the anisotropy of thermal conductivity and strength, but also other thermal, mechanical, as well as electrical and optical properties of single crystals.
Most solids have polycrystalline structure , that is, it consists of many randomly arranged crystals and does not have anisotropy of physical properties.
Natural and man-made bodies. You already know that there is a distinction between living and nonliving nature. Using fig. 9, name the bodies of living and inanimate nature.
In addition to natural bodies, there are also man-made bodies created by man. For example, during the day the room is illuminated by the natural body of the Sun, and in the evening we use man-made bodies - a table lamp or a chandelier. Seas and rivers are natural bodies, but a pool and a pond are man-made. They differ in shape, size, weight, volume.
| Rice. 9. Living and inanimate nature |
Phone characteristics These characteristics make it possible to distinguish between bodies. Agree, it is difficult to confuse a school textbook and a chicken egg, since they have different shapes. Textbook - a body of the correct shape. You can measure its length, width and height. It is impossible to measure the size of a chicken egg, since it is an irregularly shaped body.
When describing mountains, we say that these bodies of inanimate nature have large sizes, which cannot be said about a spike of wheat.
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| Water in solid, liquid and gaseous states |
There is no need to weigh a watermelon and a cherry to accurately determine that the watermelon is much heavier. Weight- This is another characteristic of bodies.
Bodies can also be characterized by volume. A bucket has a significantly larger volume than a cup. The volume of a rectangular body is determined by multiplying the value of its length, width and height. To measure the volume of an irregularly shaped body, you need to immerse it in water. The volume of the body is equal to the volume of water displaced by the body.
Characteristics of bodies- these are the signs by which they differ. The characteristics of bodies include shape, size, weight, volume. Linear dimensions, mass and volume of bodies are measured using instruments.
When characterizing bodies, pay attention to their state of aggregation. Distinguish solid, liquid, gas A penny is a solid, dew is a liquid, and air is a gas. The bodies of nature are predominantly solid.
The shape of bodies is perceived visually, that is, through vision. Using fig. 10, try to compare bodies by shape and size. Material from the site
Description of the body according to plan. Using characteristics, bodies can be described according to plan: 1) shape; 2) dimensions; 3) mass; 4) volume. Let us describe the carrots according to this plan, having first measured its length (12 cm) and mass (100 g). To determine the volume, you need to immerse the carrots in a measuring cylinder with water (Fig. 11). Let us first remember the indicators of the volume of water on the cylinder scale before immersing the carrots, and then after immersion. The difference in volume will be the volume of carrots. In this example it is approximately 30 ml.
These measurements make it possible to characterize carrots as follows: an irregularly shaped body 12 cm long, weighing 100 g and volume 30 ml.
Using the same characteristics, you can independently compare different natural and man-made bodies.
Using the size, mass, shape and volume of bodies, you can not only describe a body, but also compare it with others.
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Until now, we have considered the movement of bodies depending on time without elucidating the reasons causing these movements. The laws of dynamics establish a connection between the movement of bodies and the reasons that caused or changed this or that movement.
Let us consider the translational motion of a material point; for this we introduce dynamic characteristics with the help of which we will describe such motion. These characteristics include the concept force, mass, impulse. Let's start our consideration with the movements of bodies in reference systems, which are called inertial, and the definition of which will be given later.
1. The motion of any body in an inertial frame of reference is caused or changed only by interaction with other bodies. To describe the interaction between bodies, the concept of force is introduced, which gives a quantitative measure of this interaction.
The physical nature of the interaction can be different; there are gravitational, electrical, magnetic and other interactions (see Table 1). In mechanics, the physical nature of forces is unimportant; the question of their origin is not clarified. But for all types of interactions, their quantitative measure must be chosen in the same way. Forces of different natures must be measured using the same standards and units of measurement. Laws of mechanics universal, i.e. they describe the movement of bodies under the influence of a force of any nature. For interactions that are considered in mechanics, force can be defined as follows.
Force is a vector quantity F, which is a measure of the mechanical effect of one body on another.
Mechanical interaction can occur both between directly contacting bodies (friction force, support reaction force, etc.) and between remote bodies.
A special form of matter that connects particles of matter into single systems and transmits the action of one particle to another at a finite speed is called a physical field, or simply field.
Interactions between distant bodies are carried out through gravitational (gravity) or electromagnetic fields.
The mechanical action of a force can cause acceleration of a body or its deformation. Force is the result of the interaction of two bodies. To correctly determine the forces acting on a body, you can use the literature, which provides numerous examples.
Force F- vector - completely defined if its module (magnitude), direction in space and point of application are given. The straight line along which the vector is directed F, called line of action of the force.
If we talk about a force applied not to a material point, but to a solid body and causing its translational motion, then the effect on the body will not change when the point of action of the force is moved along the line of its action.
Simultaneous action on a material point C of several forces F 1 ,F 2 ..... F n is equivalent to the action of one force equal to their geometric (vector) sum and called resulting or resultant force (see Figure 7):
F res. = F 1 +F 2 + ..... +F n .
Figure 7 - Vector addition of forces.
The forces acting on a body or system of bodies can be divided into external And internal. Bodies that are not part of the mechanical system under study are called external and strength, acting on their part, - external. Inner forces- forces acting on a point or body from the points or bodies included in the system under consideration.
The system on which no external forces act, called isolated or closed.
2. The fundamental concept in dynamics is concept of mass m, which was not even mentioned in kinematics, was not necessary. Any material object (bodies, elementary particles, fields) has mass. Mass acts as a multilateral characteristic of the body.
It determines its gravitational properties, i.e. the forces with which a body is attracted to other bodies, in particular to the Earth.
Mass characterizes the inertial properties of the body, i.e. the body's ability to maintain a state of rest or uniform rectilinear motion, or change the speed.
The mass of a body m determines the amount of substance in a given body and is equal to the product of the density of the substance ρ by the volume V of the body:
The mass of a body, together with its speed, determines the momentum and kinetic energy of the body.
In classical mechanics, the concept of mass is characterized by the following:
- m = const, it does not depend on the state of motion of the body,
- mass - magnitude additive, i.e. the mass of the system is equal to the arithmetic sum of the masses of the bodies included in the system,
- the mass of a closed system remains unchanged during any processes occurring inside the system ( law of conservation of mass).
So, for mass we can give the following definition.
Mass is a measure of the inertia of a body or a measure of gravitational interaction.
3. Momentum of a material point is a vector quantity equal to the product of its mass and its speed P= m v.
The impulse of the system of material points is called a vector equal to the geometric (vector) sum of the momenta of all material points of the system:
P = P 1 +P 2 +.....+ P n= P i
Using the concept of mass, impulse of the system equal to the product of the mass of the entire system and the speed of its center of mass P= m v c.
Pulse P- a vector coinciding in direction with the direction of velocity.
Pulse- one of the fundamental characteristics of a physical system. Both mass and velocity have been determined previously, but only momentum has a unique property. Formulated for him conservation law impulse, which is universal by law. It is carried out both in the microworld (at the level of elementary particles, atoms and molecules), and in the macroworld (the world around us), and in the megaworld (at the level of planets, the Universe, the Galaxy). Until now, no phenomena have been discovered in which the law of conservation of momentum is violated.