Municipal Autonomous General Educational Institution
"Average comprehensive school No. 1, Svobodny
mechanical waves
Grade 9
Teacher: Malikova
Tatyana Viktorovna
The purpose of the lesson :
give students the concept of wave motion as a process of propagation of vibrations in space over time; introduce different types of waves; form an idea of the length and speed of wave propagation; show the importance of waves in human life.
Educational tasks lesson:
1. Repeat with students the basic concepts that characterize waves.
2. Review and introduce students to new facts and use cases sound waves. To teach how to fill in the table with examples from the speeches during the lesson.
3. To teach students to use interdisciplinary connections to understand the phenomena being studied.
Educational tasks of the lesson:
1. Education of worldview concepts (cause-and-effect relationships in the world, the cognizability of the world).
2. Education of moral positions (love for nature, mutual respect).
Developing tasks of the lesson:
1. Development of independent thinking and intelligence of students.
2. Development of communication skills: competent oral speech.
During the classes:
Organizing time
Learning new material
Wave phenomena observed in Everyday life. The prevalence of wave processes in nature. The different nature of the causes that cause wave processes. Wave definition. Reasons for the formation of waves in solids, liquids. The main property of waves is the transfer of energy without the transfer of matter. Characteristics two types of waves - longitudinal and transverse. Mechanism of propagation of mechanical waves. Wavelength. Wave propagation speed. Circular and linear waves.
Anchoring : demonstration of a presentation on the topic: “Mechanical
waves"; test
Homework : §42,43,44
Demos: transverse waves in the cord, longitudinal and transverse waves on the model
Frontal experiment: acquisition and observation of circular and linear waves
Video clip: circular and linear waves.
We turn to the study of the propagation of oscillations. If we are talking about mechanical vibrations, that is, about the oscillatory motion of any solid, liquid or gaseous medium, then the propagation of vibrations means the transmission of vibrations from one particle of the medium to another. The transmission of oscillations is due to the fact that adjacent sections of the medium are interconnected. This connection can be carried out in various ways. It can be caused, in particular, by the elastic forces arising from the deformation of the medium during its vibrations. As a result, a vibration caused in any way in one place entails the successive occurrence of vibrations in other places, more and more remote from the original, and a so-called wave is obtained.
Why do we study wave motion at all? The fact is that wave phenomena have great value for everyday life. These phenomena include the propagation of sound vibrations, due to the elasticity of the air around us. Thanks to elastic waves, we can hear at a distance. Circles running up on the surface of the water from a thrown stone, small ripples on the surface of lakes and huge ocean waves are also mechanical waves, although of a different type. Here, the connection of adjacent sections of the water surface is not due to elasticity, but to the force of gravity or the forces of surface tension.
Tsunamis are huge ocean waves. Everyone has heard of them, but do you know why they form?
They occur mainly during underwater earthquakes, when there are rapid displacements of sections of the seabed. They can also occur as a result of explosions of underwater volcanoes and strong landslides.
In the open sea, tsunamis are not only not destructive, but, moreover, they are invisible. The height of the tsunami waves does not exceed 1-3 m. If such a wave, which has a huge supply of energy, rapidly sweeps under the ship, then it will only gently rise, and then just as smoothly descend. And the tsunami wave sweeps through the ocean spaces truly rapidly, at a speed of 700-1000 km / h. For comparison, a modern jet liner flies at the same speed.
Having arisen, a tsunami wave is able to travel thousands and tens of thousands of kilometers across the ocean, almost without weakening.
Being completely safe in the open ocean, such a wave becomes extremely dangerous in the coastal zone. She puts all her unspent huge energy into a crushing blow to the shore. At the same time, the wave speed decreases to 100-200 km / h, while the height increases to tens of meters.
Last time The tsunami hit Indonesia in December 2004 and claimed the lives of over 120,000 people and made over a million people homeless.
That is why it is so important to study these phenomena and, if possible, prevent such tragedies.
In the air, not only sound waves can propagate, but also destructive blast waves. Seismic stations record ground vibrations caused by earthquakes occurring thousands of kilometers away. This is possible only because seismic waves propagate from the place of the earthquake - fluctuations in earth's crust.
A huge role is also played by wave phenomena of a completely different nature, namely electromagnetic waves. The phenomena caused by electromagnetic waves include, for example, light, the importance of which for human life can hardly be overestimated.
In later lessons, we'll look at the use of electromagnetic waves in details. In the meantime, let's return to the study of mechanical waves.
The process of propagation of oscillations in space over time is called wave . The particles of the medium in which the wave propagates are not transferred, they only oscillate around their equilibrium positions.
Depending on the direction of particle oscillations with respect to the direction of wave propagation, there are longitudinal and transverse waves.
Experience. Hang a long cord at one end. If the lower end of the cord is quickly taken to the side and returned back, then the “bend” will run up the cord. Each point of the cord oscillates perpendicular to the direction of wave propagation, that is, across the direction of propagation. Therefore, waves of this type are called transverse.
What results in the transfer of oscillatory motion from one point of the medium to another, and why does it occur with a delay? To answer this question, we need to understand the dynamics of the wave.
Displacement towards the lower end of the cord causes deformation of the cord at this point. Elastic forces appear, tending to destroy the deformation, that is, tensions appear that pull the immediately adjacent section of the cord following the section displaced by our hand. The displacement of this second section causes deformation and tension of the next one, and so on. The sections of the cord have mass, and therefore, due to inertia, they do not gain or lose speed under the action of elastic forces instantly. When we brought the end of the cord to the greatest deviation to the right and began to lead it to the left, the adjacent section will still continue to move to the right, and only with some delay will stop and also go to the left. Thus, the delayed transition of the vibration from one point of the cord to another is explained by the presence of elasticity and mass in the material of the cord.
direction propagation direction
wave oscillations
The propagation of transverse waves can also be shown using a wave machine. White balls simulate the particles of the medium, they can slide along the vertical rods. The balls are connected by threads to the disk. When the disc rotates, the balls move in concert along the rods, their movement resembles a wave pattern on the surface of water. Each ball moves up and down without shifting to the sides.
Now let's pay attention to how the two extreme balls move, they oscillate with the same period and amplitude, and at the same time they are either in the upper or in the lower position. They are said to oscillate in the same phase.
The distance between the nearest points of a wave oscillating in the same phase is called wavelength. The wavelength is denoted by the Greek letter λ.
Now let's try to simulate longitudinal waves. As the disc rotates, the balls oscillate from side to side. Each ball periodically deviates either to the left or to the right from the equilibrium position. As a result of oscillations, the particles either approach each other, forming a clot, or diverge, creating a rarefaction. The direction of the ball oscillations coincides with the direction of wave propagation. Such waves are called longitudinal.
Of course, the definition of wavelength remains in full force for longitudinal waves.
Direction
wave propagation
oscillation direction
Both longitudinal and transverse waves can only occur in an elastic medium. But in any? As already mentioned, in a transverse wave, the layers are shifted relative to each other. But elastic forces in shear arise only in solids. In liquids and gases, adjacent layers freely slide over each other without the appearance of elastic forces. And since there are no elastic forces, then the formation of transverse waves is impossible.
In a longitudinal wave, sections of the medium experience compression and rarefaction, that is, they change their volume. Elastic forces with a change in volume arise both in solids, and in liquids, and in gases. Therefore, longitudinal waves are possible in bodies that are in any of these states.
The simplest observations convince us that the propagation of mechanical waves does not occur instantaneously. Everyone has seen how gradually and evenly the circles on the water expand or how the waves of the sea run. Here we directly see that the propagation of vibrations from one place to another takes a certain time. But for sound waves, which are invisible under normal conditions, it is easy to detect the same thing. If there was a shot in the distance, a whistle of a locomotive, a blow to some object, then we first see these phenomena and only after some time hear the sound. The farther away from us the sound source, the greater the delay. The time interval between a flash of lightning and a thunderclap can sometimes reach up to several tens of seconds.
For a time equal to one period, the wave propagates over a distance equal to the wavelength, so its speed is determined by the formula:
v=λ /T or v=λν
Task: the fisherman noticed that in 10 seconds the float makes 20 oscillations on the waves, and the distance between adjacent wave crests is 1.2 m. What is the speed of wave propagation?
Given: Solution:
λ=1.2 m T=t/N v=λN/t
v-? v=1.2*20/10=2.4 m/s
Now back to the types of waves. Longitudinal, transverse ... And what other waves are there?
Let's watch a movie clip
Spherical (circular) waves
Plane (linear) waves
The propagation of a mechanical wave, which is a successive transfer of motion from one section of the medium to another, means thereby the transfer of energy. This energy is delivered by the wave source when it sets in motion the layer of the medium adjacent to it. From this layer, energy is transferred to the next layer, and so on. When a wave encounters various bodies, the energy it carries can produce work or be converted into other forms of energy.
A striking example such a transfer of energy without transfer of matter give us blast waves. At distances of many tens of meters from the site of the explosion, where neither fragments nor a stream of hot air reach, the blast wave knocks out glass, breaks walls, etc., that is, it produces a large mechanical work. We can observe these phenomena on TV, for example, in war films.
The transfer of energy by a wave is one of the properties of waves. What other properties are inherent in waves?
reflection
refraction
interference
diffraction
But we will talk about all this in the next lesson. And now let's try to repeat everything that we learned about waves in this lesson.
Questions to the class + demonstration of a presentation on this topic
And now let's check how well you learned the material of today's lesson with the help of a small test.
Lesson topic: “Mechanical waves and their types. Wave Characteristics»
Lesson Objectives:
Educational: form an idea of the wave process, types of mechanical waves and the mechanism of their propagation, determine the main characteristics of wave motion.
Developing: develop the ability to highlight the main thing in the text, analyze information, systematize information by compiling a summary.
Educational: to promote the development of independence, self-government, to form respect for comrades and their opinion.
During the classes
1. Organizational moment. Introduction by the teacher.
In the previous lessons, we considered the topic: "Oscillatory motion." The knowledge gained in the study of this topic will help us in today's lesson. We need to remember the following concepts.
Test "Oscillation movement". Slide number 1.
Instructions for working with the test: match the numbers of questions and answers and enter them in the forms that are on each table.
Questions:
1. Under what conditions do oscillations occur?
2. What is the restoring force?
3. What oscillation is harmonic?
4. What is called the oscillation period?
5. Define the unit - Hertz.
6. What is called the oscillation frequency?
7. What is amplitude?
8. What is a phase?
9. Hesitant material points have the same phase. What does this mean?
10. Oscillating material points have opposite phases. What does this mean?
Answers:
1. ... the frequency at which one complete oscillation takes place in 1 s.
2. ... the greatest deviation of the oscillating point from the equilibrium position.
3. ... the number of complete oscillations in 1 s.
4. ... a value showing what part of the period has passed from the moment the oscillations began to a given moment in time.
5. …when external forces impart energy to material particles (bodies) and a restoring force acts on them.
6. ... a force whose direction is always opposite to the displacement.
7. ...points oscillate along parallel paths and move in the same direction at any time.
8. ...points oscillate along parallel paths and move in opposite directions at any time.
9. ... oscillations that occur under the action of a restoring force directly proportional to the displacement of the oscillating point.
10. ... the time for which one complete oscillation takes place.
Key. Slide number 4.
Questions | ||||||||||
Answers |
Cross-validation test.
Teacher. Each of you has a sheet with a blank on the table - a diagram of the future reference abstract. In the course of study new topic we will fill in this chart and get a summary that will help you prepare for the next lesson.
LESSON 7/29
Subject. mechanical waves
The purpose of the lesson: to give students the concept of wave motion as a process of propagation of vibrations in space over time.
Type of lesson: lesson learning new material.
LESSON PLAN
Knowledge control |
1. Energy conversion during vibrations. 2. Forced vibrations. 3. Resonance |
|
Demonstrations |
1. Formation and propagation of transverse and longitudinal waves. 2. Fragments of the video film "Transverse and longitudinal waves" |
|
Learning new material |
1. Mechanical waves. 2. Main characteristics of waves. 3. Interference of waves. 4. Transverse and longitudinal waves |
|
Consolidation of the studied material |
1. Qualitative questions. 2. Learn to solve problems |
STUDY NEW MATERIAL
The sources of waves are oscillating bodies. If such a body is in any medium, the vibrations are transmitted to the adjacent particles of matter. And since the particles of matter interact with each other, the oscillating particles transmit vibrations to their "neighbors". As a result, vibrations begin to propagate in space. This is how waves form.
Ø A wave is the process of propagation of oscillations over time.
Mechanical waves in the medium are caused by elastic deformations of the medium. The formation of a wave of one kind or another is explained by the presence of force bonds between the particles participating in the oscillations.
Any wave carries energy, because a wave is an oscillation propagating in space, and any oscillation, as we know, has energy.
Ø A mechanical wave transfers energy, but does not transfer matter.
If the wave source makes harmonic vibrations, then each point of the given medium, in which the oscillations propagate, also performs harmonic oscillations, and with the same frequency as the source of the waves. In this case, the wave has a sinusoidal shape. Such waves are called harmonic. The maximum of a harmonic wave is called its crests.
As an example, consider a wave that travels along a cord when one end oscillates under the action of an external force. If we observe any point on the cord, we will notice that each point oscillates with the same period.
Ø The period of time T, during which one complete oscillation occurs, is called the oscillation period.
A complete oscillation occurs during the time when the body returns from one extreme position to this extreme position.
Ø Oscillation frequency v is called physical quantity, equal to the number of oscillations per unit of time.
Ø The module of the greatest deviation of particles from the equilibrium position is called the amplitude of the wave.
The wave period and its frequency are related by:
The unit of oscillation frequency is called hertz (Hz): 1 Hz = 1/c.
Ø The distance between the nearest points of the wave, which move in the same way, is called the wavelength and is denoted by λ.
Since waves are vibrations propagating in space over time, let's find out what is the speed of wave propagation. For a time equal to one period T, each point of the medium carried out exactly one oscillation and returned to the same position. So, the wave has shifted in space exactly by one wavelength. Thus, if we denote the speed of wave propagation, we get that the wavelength is equal to:
λ = T .
Since T \u003d 1 / v, we find that the wave speed, wavelength and wave frequency are related by the relation:
= λv .
Waves from different sources propagate independently of each other, due to which they freely pass through one another. Superimposing waves with the same lengths, one can observe the amplification of waves at some points in space and attenuation at others.
Ø Mutual amplification or weakening in space of two or more waves with the same length is called wave interference.
Mechanical waves are transverse and longitudinal:
Particles of a transverse wave oscillate across the direction of wave propagation (in the direction of energy transfer), and parts of a longitudinal wave oscillate along the direction of wave propagation.
Ø Waves in which particles of the medium during oscillations are displaced in a direction perpendicular to the direction of wave propagation are called transverse.
Transverse waves can only propagate in solids. The fact is that such waves are caused by shear deformations, and in liquids and gases there are no shear deformations: liquids and gases do not “resist” a change in shape.
Ø Waves in which particles of the medium during oscillations are displaced along the direction of wave propagation are called longitudinal.
An example of a longitudinal wave is a wave that runs along a soft spring when one of its ends oscillates under the action of a periodic external force directed along the spring. Longitudinal waves can propagate in any medium. The relation = λ v and λ = T are valid for both types of waves.
QUESTION TO STUDENTS DURING THE PRESENTATION OF NEW MATERIAL
First level
1. What are mechanical waves?
2. Is the wavelength of the same frequency the same in different media?
3. Where can transverse waves propagate?
4. Where can longitudinal waves propagate?
Second level
1. Are transverse waves possible in liquids and gases?
2. Why do waves carry energy?
CONFIGURATION OF THE STUDYED MATERIAL
WHAT WE LEARNED IN THE LESSON
A wave is the process of propagation of oscillations over time.
The period of time T during which one complete oscillation occurs is called the oscillation period.
· Oscillation frequency v is a physical quantity equal to the number of oscillations per unit of time.
· The distance between the nearest points of the wave, which move in the same way, is called the wavelength and is denoted by λ.
Mutual amplification or weakening in space of two or more waves of the same length is called wave interference.
Waves in which particles of the medium during oscillations are displaced in a direction perpendicular to the direction of wave propagation are called transverse.
Waves in which particles of the medium during oscillations are displaced along the direction of wave propagation are called longitudinal.
Riv1 No. 10.12; 10.13; 10.14; 10.24.
Riv2 No. 10.30; 10.46; 10.47; 10.48.
Riv3 No. 10.55, 10.56; 10.57.
"Who dares to say
that we all know
what can be known?
G. Galileo.
Lesson topic: "Mechanical waves".
North Ossetia-Alania, Mozdok district, MBOU secondary school with. Grape
Academic subject: Physics
Lesson topic:“Propagation of an oscillation in a medium. Waves»
The place of the lesson in the structure of the lesson:« Mechanical vibrations.Waves. Sound"
Content Goals:
Educational : withform ideas on the concept of mechanical vibrations wave. Reveal the nature, study the cause of the wave Educational : develop logical thinking; application techniques mental activity clarification, deepening, awareness and strengthening of knowledge interest in learning and research processes, develop the ability to highlight the main thing, argue your answer, give examples.
educators : bring up attentiveness, concentration, perseverance in achieving the goal. Willpower, curiosity, help students see the practical benefits of knowledge.
Planned educational results:
subject – to know and understand the meaning of the meaning of a mechanical wave.
metasubject:
Regulatory - set a goal, evaluate your work; correct and explain your mistakes.
Communicative - engage in dialogue. Be able to listen and hear, express your thoughts, build statements, participate in collective discussion problems, take into account the positions of others.
cognitive - analyze the learning situation; develop operations of thinking; set a task based on the correlation of what is known, semantic reading; the ability to adequately, consciously and arbitrarily speech statements in oral and writing, transferring the content of the text in accordance with the purpose and compliance with the norms of constructing the text; highlighting is significant.
Personal : to form interest and practical skills, independence in acquiring knowledge about a mechanical wave, a value relationship to each other, to the teacher, to the learning outcome, to develop initiative.
Technologies used : technology critical thinking, collaborative learning technology, information and communication technology.
Information Technology Resources :
List of used sources and literature :
Textbook "Physics Grade 9" A, V. Peryshkin EAT. Gutnik Tutorial for educational institutions 2nd edition - M: Bustard, 2014
Lukashnikov.I. collection of tasks in physics for grades 7-9 of educational institutions - M: education
COR in physics Grade 9
Equipment : for experiment: spring, wave machine, geographic map
Lesson type Learning new
Teaching methods Conversation. Demonstration of experiences. Notes on the board and in a notebook. Deductive application theoretical knowledge.
During the classes
1. Organizational moment
Greetings.
A brief mood for productive work.
2.Front survey
Formation of the topic of the lesson and the purpose of the lesson. Understanding and accepted by the children the objectives of the lesson
Creation problem situation
a) Analysis of formulas and units of measurement.
E-frequency
T - number of oscillations
N - energy
l - oscillation time
v - amplitude
b) Poll on questions
1.Give an example oscillatory motion?
2.What fluctuations do you know?
3. Studying a new topic.
Inclusion of students in purposeful activities.
Let's find a connection between oscillations and a wave. Let's turn to a simple experiment. We fix the spring with one ring, and hit the other end with our hand. From the impact, several coils of the spring come together, an elastic force arises, under the influence of which these coils begin to diverge. As the pendulum passes in its equilibrium movement, so the coils, bypassing the equilibrium position, will continue to diverge. As a result, some vacuum is formed in this place of the spring. If the end of the spring is rhythmically struck by hand, then with each blow the coils will approach each other, forming a thickening and moving away from each other, forming a vacuum.
Perturbations propagating in space moving away from their place of origin is called a wave. The simplest type of oscillation is waves that arise on the surface of a liquid and radiate from the place of disturbance in the form of concentric circles.
Such waves can arise not only in liquids and gases, but also in solids.
A wave arises only when, together with an external perturbation, forces appear in the medium that counteract it. Usually these are elastic forces.
Mechanical waves arise and mix only in elastic media. This is what allows the particles in the wave to transfer excess energy to neighboring particles. In this case, the particles, having transferred part of the energy, return to their original position. This process continues. Thus, the matter in the wave does not move. The particles of the medium oscillate around their equilibrium positions. Therefore, in a traveling wave, energy is transferred without transfer of matter.
Depending on the direction in which the particles oscillate relative to the direction of movement of the wave, longitudinal and transverse waves are distinguished.
In a longitudinal wave, the particles oscillate in directions that coincide with the movement. Such waves arise as a result of compression and tension.
Therefore, they can occur in gases, liquids and solids.
In a transverse wave, particles oscillate in planes perpendicular to the direction of wave travel. Such waves are the result of shear deformation. Therefore, waves can only arise in solids. For in gases and liquids this type of deformation is impossible.
Demonstration of a wave using a wave machine.
Film screening 5 minutes.
The wave phenomenon in elastic media is characterized by certain values, these include:
E-wave energy
A - wave amplitude
v-wave frequency
T - wave period
Wave speed
Wavelength
The speed of mechanical waves, depending on the type of wave, can vary from hundreds of m/s to 10 km/s
The length of a mechanical wave is understood as the distance that the wave travels in a time equal to the period of oscillation.
Formulas: Invite students to write their own formulas
Oscillations that form in the solid part of the Earth during various tectonic processes or during underground nuclear explosions called seismic waves.
In the solid part of the Earth, both longitudinal and transverse waves can form.
Longitudinal waves compress and stretch the rocks through which they pass. Longitudinal waves are the fastest. Their speed reaches about 8 km / s, and the speed of transverse waves is 4.5 km / s. The difference in the velocities of the two types of waves makes it possible to determine the epicenter of earthquakes and is recorded by a seismograph instrument. Seismologists try to predict where and when an earthquake might occur so that people can prepare for it. Every 5 minutes, one earthquake occurs on Earth. Hundreds of thousands of earthquakes are recorded every year on the globe. From time to time there are those that violate the integrity of the soil, destroy buildings and lead to human casualties. There are two scales for recording an earthquake, the Richter scale and the Mercalle scale.
The Richter scale measures the strength of seismic waves. Presentation - (Table)
The Merkell scale measures the consequences of earthquakes associated with human casualties and the destruction of buildings. A weak earthquake can have more serious consequences than even very powerful ones if they occur in a city where there are many buildings and where many people live.
Here are some earthquakes of the last century that had catastrophic consequences. (Presentation)
1960 Morocco Agadar
1966 24.04. Tashkent plant 8 points
1969 May 28, Turkey 7.5 points
1969 In 22 states of America 5-7 points
1976 Thai plant 7-8 points 20 thousand people
AT last years Turkey, Japan.
Predicting an earthquake is a very difficult task.
There are large areas where there is no earthquake at all and there are areas of frequent earthquakes.
Two areas: Work on the map (the student shows the areas on the map)
Pacific ring - covers the coast of Kamchatka, Alaska coast North America turns to Australia, through Indonesia, the coast of China, captures Japan and ends in Kamchatka.
The second region is the Mediterranean-Asian. They pass in a wide strip from Portugal and Spain - through Italy, the Balkan Peninsula, Greece, Turkey, the Caucasus, the countries of Asia Minor enter the Baikal region and then merge onto the Pacific coast.
People have always tried to reduce the effects of earthquakes and built special buildings in earthquake-prone areas that could withstand significant tremors. Science cannot but warn, predict these phenomena generated by the force of nature. But work in this area is underway.
Here are some of them.
Before an earthquake, the concentration of radon in water increases, and a few days before the disaster, it normalizes.
Good at predicting earthquakes animal world. Mass migration of ants, snakes and lizards leave their homes.
Deep-sea fish are thrown ashore, whiskered cod, eel. Dogs, elephants, hippos. (Presentation)
Ultrasound can be a warning signal.
4. Rest and mood for subsequent work.
Physical education minute.
5. Verification work .
Consolidation of the material through group and individual work (mutual verification). Grading.
6. Ensuring children understand the purpose, content and methods of doing homework
2. Composition and solve the problem according to the schedule
3. Prepare a message on the topic "tsunami".
The teacher gives differentiated homework taking into account the individual abilities of children.
7. The results of the lesson, reflection.
Can you name the topic of the lesson?
What new did you learn at the lesson today?
