imagine that such a mechanical wave, can be throwing a stone into the water.Circles occurring therein and being alternating troughs and crests, - an example of mechanical waves.What is their essence?Mechanical waves - a process of wave propagation in elastic media.
water waves
Such mechanical waves exist due to the effect on the fluid particles and intermolecular forces of gravity.People have long been studying the phenomenon.Most notable are the ocean and the waves of the sea.With increasing wind speed are changed, and their height increases.It is also complicated and shape the waves themselves.In the ocean, they can reach frightening proportions.One of the most obvious examples are the forces tsunami, sweeping away everything in its path.
energy of the sea and ocean waves
reached the shore, the waves with a sharp change in the depth increases.They sometimes reach a height of several meters.At such moments the kinetic energy of the enormous mass of water transferred coastal barriers, which under its influence rapidly destroyed.The strength of the tide sometimes reaching ambitious values.
Elastic waves
The study not only the mechanics of vibrations on the surface of the liquid, but also the so-called elastic waves.This disturbance, which are distributed in different environments under the influence of elastic forces in them.Such outrage is any deviation of particles of the medium from its equilibrium position.A good example of elastic waves is a long rope or a rubber tube, one end attached to anything.If it is taut, and then create a lateral jerk at the second (non-bound) of its end outrage, we can see it along the entire length of the rope "could run" to support and be reflected back.
Source mechanical waves
initial perturbation leads to a wave in the medium.It is caused by the action of a foreign body, which in physics is called the source of the wave.They can be a human hand, swaying rope, or a pebble thrown into the water.In the case where the source of the action is short-lived in the environment is often a solitary wave.When the "troublemaker" makes long oscillatory motion, waves begin to appear one after another.
Terms appearance mechanical waves
Such fluctuations are not always formed.A prerequisite for their appearance is the appearance at the time of the disturbance protection preventing him strength, particularly elastic.They seek to bring together neighboring particles when they are separated, and alienate them from each other at the time of convergence.The elastic force acting on the remote from the source of disturbance particles begin to remove them from the balance.Over time, the particles of the medium involved in an oscillatory motion.The spread of such fluctuations and a wave.
mechanical waves in an elastic medium
The elastic wave there are two kinds of motion simultaneously: fluctuations of particles and distribution of the disturbance.It called longitudinal mechanical wave particles which range along the direction of its propagation.Called transverse wave, particles of the medium which vary across the direction of its propagation.
properties of mechanical waves
disturbances in the longitudinal wave is a vacuum and compression, and lateral - shift (offset) between layers of protection against others.Compressive strain is accompanied by elastic forces.At this shear strain associated with the appearance of the elastic forces exclusively in solids.The gaseous and liquid media shifting layers of these media is not accompanied by the appearance of the said forces.Due to its properties longitudinal waves can propagate in any media, and cross - only in hard.
Features of water waves
waves on the surface of the liquid is not longitudinal and transverse.They are more complex, the so-called longitudinal and transverse character.In this case, the fluid particles move circumferentially or elongated ellipse.The circular motion of particles on the surface of the liquid, especially for large vibrations, accompanied by their slow but continuous motion in the direction of wave propagation.It is these properties of mechanical waves in the water causes the appearance on the shores of various seafood.
frequency mechanical waves
If the elastic medium (liquid, solid, gas) to excite the oscillation of its particles, the result of the interaction between them, it will be distributed at a rate of u.Thus, in the gaseous or liquid medium will be oscillating body, its movement is transmissible to all the adjacent particle.They will be involved in the process of following and so on.In this environment point everything will oscillate the same frequency equal to the frequency of the oscillating body.It is the frequency of the wave.In other words, this value can be described as the frequency of oscillations of the points in the environment, where the wave propagates.
immediately be unclear how this process occurs.With mechanical waves associated energy transfer of the vibrational motion from its source to the periphery of the medium.In the course of which a so-called periodic strain carried by a wave from one point to another.In doing so, the particles of the medium with the wave does not move.They range close to its equilibrium position.That is why the propagation of mechanical waves is not accompanied by transferring substance from one location to another.In the mechanical waves of different frequencies.Therefore, they are divided into bands and created a special scale.Frequency is measured in hertz (Hz).
basic formulas
Mechanical waves, calculation formulas are fairly simple, it is an interesting object for study.Wave velocity (υ) - is the speed of movement of its front (the locus of all the points, which came fluctuation environment at the moment):
υ = √G / ρ,
where ρ - density of the medium, G - modulus of elasticity.
When calculating do not confuse the speed of mechanical waves in a medium with the velocity of the particles of the medium, which are involved in the wave process.Thus, for example, the sound wave propagates through the air at an average speed fluctuations of its molecules at 10 m / s, while the velocity of the sound waves in normal conditions is 330 m / s.
wave front can be of different types, the simplest of which are:
• Spherical - caused by fluctuations in the gaseous or liquid medium.The amplitude of the wave at the same time decreases with increasing distance from the source is inversely proportional to the square of the distance.
• Flat - a plane that is perpendicular to the direction of wave propagation.It arises, for example, in a closed piston cylinder when the latter oscillates.The plane wave is characterized by almost constant amplitude.Her slight decrease with increasing distance from the source of the disturbance associated with the viscosity of the liquid or gaseous medium.
Wavelength
Under wavelength understand the distance that it will be moved to the front for the time equal to the period of oscillation of particles of the medium:
λ = υT = υ / v = 2πυ / ω,
where T - the period of oscillation,υ - velocity of the wave, ω - angular frequency, ν - the frequency of oscillation points of the medium.
Since the speed of propagation of mechanical waves is totally dependent on the properties of the medium, its length λ during the transition from one medium to another changes.The oscillation frequency ν always remains the same.Mechanical and electromagnetic waves are similar in that their distribution is carried out in the energy transfer, but there is no transfer of matter.
