Physics lesson for grade 9 “Sound. Echo. Sound reflection.
assimilation of a new type of mechanical vibrations and waves; formation of concepts: acoustics, infrasound, sound, ultrasound.
broadening the horizons of students through the integration of knowledge;
deepening knowledge using visual and sound information;
3) development of skills of active independent activity;
4) the development of logical and abstract thinking, intellectual and creative abilities.
development of cognitive interest in the subject; promoting positive motivation in learning; creation of conditions for the education of a culture of mental labor; contributing to the awakening of spiritual, civic and Patriotic feelings.
Learning tools: cards, student messages, video.
The world of sounds is so diverse
Rich, handsome, diverse.
But all of us are tormented by the question:
Where do the sounds come from
What do our ears always delight?
2. Definition of the topic of the lesson and goal setting
3. The study and consolidation of new material
4. Testing new knowledge
5. Communication of additional knowledge
6. Homework Information
Good afternoon! Please sit down. Today’s physics lesson is unusual. Guests have come to us. I would like to hope that their presence will contribute to a more serious and responsible attitude to the lesson, and you will have a desire to demonstrate strong knowledge of the subject.
Definition of the topic of the lesson and goal setting.
In past classes, we studied mechanical vibrations and waves. Today we continue our acquaintance with another type of mechanical vibrations.
The theme of today’s lesson is “Sound. Echo. Sound reflection. Ultrasound. Infrasound. " The purpose of our lesson is to get acquainted with sounds, their sources, with a variety of sounds through acquaintance with information about ultrasound and infrasound.
Open notebooks, write down the date, topic of the lesson.
The section of physics in which sound phenomena, sounds and their properties are studied is called “acoustics”. Write down the definition of a new concept: “Acoustics. section of physics in which sound phenomena, sounds and their properties are studied ”
In the world around us, we hear a variety of sounds. They are an integral part of the world around us. Not everyone knows how they are formed and distributed. Therefore, in the lesson you have to get acquainted with the nature of sounds.
The study and consolidation of new knowledge.
Man lives in a world of sounds. The sound is caused by mechanical vibrations in an elastic medium and bodies whose frequencies lie in the range: from 16 to 20,000 Hz, and are perceived by the hearing organs. Mechanical vibrations, the frequency of which is less than 16 Hz, are called infrasounds, and vibrations with frequencies of more than 20,000 Hz. by ultrasounds.
Any body (solid, liquid or gaseous), oscillating with sound frequency, creates a sound in the environment. Oscillations from the body are transmitted to the air and propagate in it in the form of a sound wave. Among sound sources there are both natural and artificial. An example of the natural formation of sound waves in the air is the formation of thunder during lightning discharges. The physics of this phenomenon is that near the lightning discharge channel the air is heated to a very high temperature and its expansion leads to the formation of a shock wave. She then gradually goes into sound vibrations. Examples of artificial sources of sound are tuning fork, musical instruments, bells. Having heard some sound, we can establish that it reached us from the source. To make a sound, the subject must hesitate. So, for example, the membrane oscillates in the reproducer. light disk fixed around its circumference. If the sound is made by a musical instrument, then the sound source. an oscillating pillar of air in it.
Between the sounding body (sound source) and the ear (sound receiver) is a substance that transmits sound vibrations from the sound source to the receiver. Most often, such a substance is air. Oscillating air molecules hit the eardrum, because of this it also oscillates. These vibrations go further through the bone tissue and fluid in the ear, until they reach the auditory nerve, and it sends a signal to the brain.
Conditions and speed of distribution.
A prerequisite for the emergence and propagation of sound. the presence of an elastic medium: gas, liquid, solid. Diving with your head while swimming, you can hear the sound of a blow of two stones, produced at a great distance. With your head on the rails, you can hear the sound of an approaching train. Good sound conducts the earth. Sound cannot propagate in airless space (vacuum), because there is nothing to hesitate.
The sound wave is longitudinal. It is a sequence of contractions and
tensile elastic medium, propagating not instantly, but with a certain finite speed. In a warm environment, the speed of sound is greater than in a cold environment. The speed of sound in air at a temperature of 0 0 C is 330 m / s; in water. about 1500 m / s; in steel. 5000 m / s.
According to the action made on us, all sounds are divided into two groups: musical sounds and noises. It is essential for a musical sound that vibrations occur at regular intervals. Fluctuations of strings, tuning forks, etc. have such a character. Oscillations of trains, tree branches, etc. occur at irregular intervals, therefore, the sounds they produce represent only noise.
Ultrasound and its application
Ultrasound. elastic waves of high frequency. Ultrasonic vibrations are found in nature: in the noise of wind, waterfall, surf, forest. Some animals not only perceive, but also emit ultrasounds. Bats, dolphins use ultrasonic pulses to detect obstacles.
Ultrasound has been widely used in industry, medicine, and also in agriculture. Here are some details about using ultrasound.
Soaked for sowing seeds of melon, zucchini are processed for 3 minutes by ultrasound. As a result, melons ripen 8 days earlier, and the yield is 25% higher than without treatment. After ultrasonic treatment, tomato yield increases by 20%, the vitamin C content in fruits increases by 1.5 times, and sugar content increases by 2%.
Video: How To Distinguish Rumor Does an Electric Drill Work
Ultrasonic cotton seeds are barely exposed in 4.5 minutes. This makes it possible to introduce trace elements into them. Thanks to this, pathogens are completely destroyed, the rate of germination and the cold resistance of seeds are markedly increased. Cotton ripens a month earlier, and its yield is 1.5 times higher.
Ultrasound is used to control insects. Ultrasonic vibrations with a frequency of 50 kHz. enemies of caterpillars. Hearing these sounds the caterpillars leave the field. Oscillations with a frequency of 200 kHz destroy the respiratory organs of mosquito larvae, and they die.
Various animals often die under the wheels of cars. hares, foxes, goats, badgers, etc. Significant damage to nature.
An original device has been created to warn animals about the approach of a car. A small device emits ultrasound, which is perceived by animals at a distance of 200. 400 meters and keeps them away from the road. The device can be installed on any car. It is necessary when driving along forest and mountain roads, at night and in the wee hours.
Ultrasonic signals are also used by some jagged whales. These signals allow them to hunt squid in the complete absence of light.
It was also established that ultrasonic waves with a frequency of more than 25 kHz cause pain in birds. This is used, for example, to deter gulls from ponds with drinking water.
In industry, defects in products are judged by the reflection of ultrasound from cracks in metal castings.
Ultrasounds break up liquid and solid substances.
In medicine, ultrasound is used to weld broken bones, detect tumors, carry out diagnostic tests in obstetrics, etc.
One of the most common procedures with its use. Ultrasound, where ultrasound is used to diagnose the condition of internal organs. Ultrasound physiotherapy is also used to accelerate the regeneration of scars, tissues, bone fusion; ultrasound cardiogram, ultrasound osteosynthesis. (The biological effect of ultrasound (leading to the death of microbes) allows it to be used to sterilize milk, drugs, and medical instruments.
Composer Beethoven, having lost his hearing, remained in complete silence, used the properties of solids to conduct sound better and listened to music, holding a stick in his teeth with one end and the other, holding it to the piano.
Infrasound and its use
The human ear does not perceive infrasound waves. Despite this, they are able to exert certain physiological effects on a person.
Special experiments have shown that irradiating people with sufficiently intense infrasound can cause a loss of a sense of balance, nausea, involuntary rotation of the eyeballs, etc. For example, at a frequency of 4-8 Hz, a person feels the movement of internal organs, and at a frequency of 12 Hz. an attack of motion sickness.
Infrasound we do not hear, but we feel. After all, we live in a world of infrasound. The wind blows over buildings, tree trunks, poles. infrasound is born. A car rushes, and an infrasonic loop stretches behind it. A plane flies, and low-frequency sound waves come from it. Infrasound occurs during volcanic eruptions, during lightning discharges and the operation of various devices.
It has long been noticed that jellyfish and fish go far from the coast long before the storm. So they feel the approach of the storm. But in what way? There is reason to believe that infrasound. It is formed when the wind moves over the crests of the waves and overtakes the storm.
Scientists have tried to make a device that senses infrasound. Nowadays, such devices are on coast stations, on ships. The storm is still far away, it will come another fifteen, twenty hours later, and the device is already signaling an approaching bad weather, warns of impending danger.
American scientists have discovered that tigers and elephants use
for communication with each other, not only growl, purr or roar and trumpet calls, but also infrasound, that is, sound signals are very
low frequency, inaudible to the human ear.
Testing new knowledge.
The decision of computing problems
When a school of fish was detected with an echo sounder, it was noticed that the moments of sending and receiving an audio signal were separated by a time interval of 0.7 seconds. What distance is the school of fish at if the speed of sound in water is 1400 m / s?
What is the depth of the sea if the sound signal sent with the help of sonar returned back after 0.9 s? The speed of sound in water is considered equal to 1400m / s.
The solution to quality problems.
Can the sound of a strong explosion on the moon be heard on Earth?
Answer. Not. The sound of an explosion on the Moon cannot be heard on Earth, since sound is a mechanical wave, and mechanical waves can only propagate in an elastic medium, whereas there is an airless space between the Earth and the Moon.
Who more often flaps wings during flight. mosquito or fly?
Decision:
The sound made by a flying mosquito is noticeably higher in tone than the sound made by a fly. The frequency of sound (and hence the pitch) is determined by the frequency of oscillation of the wings of the insect. Therefore, the frequency of oscillation of the wings of a mosquito is greater.
How to distinguish by ear. Does the electric drill idle or drill a hole?
A free-running drill makes more revolutions per unit of time, so the sound created by it will be higher.
Excerpt from A. Solzhenitsin’s book “In the First Circle”: “Only space disasters occur silently. If a New Star burst behind our shoulders. we wouldn’t even hear. ”
Question: Why do not we hear the explosion of the New Star? (We will not hear the explosion of the New Star, because there is a vacuum in world space, there sound cannot propagate).
Why do we first see a flash of lightning and only after a while we hear the thunder? (The speed of light is greater than the speed of sound, so we first see a flash of lightning and only after a while we hear the sound of thunder).
Task (Clever reptiles).
Residents of the southern regions of Kazakhstan know that lizards and snakes crawl out of their holes to an earthquake. How to explain this? (Lizards and snakes perceive infrasound waves (inaudible "buzz" of the Earth), which precedes this formidable phenomenon).
Heavy rain can be distinguished from small rain by the sound that occurs when the drops fall on the roof. What is such an opportunity based on? (large droplets strike with greater force and excite vibrations of greater amplitude. Therefore, a louder sound is heard from them).
Task (Ear to the ground).
Why do the heroes of fairy tales and legends usually kneel down and drop their ears to the ground to discover the distant, invisible horsemen? If you can hear the distant clatter of hooves through the earth, then why is this sound not heard in the air? (The fact that sound in the earth propagates faster than in air does not matter in this case, since the horse’s speed is much less than the speed of sound. Sound travels better in the ground because there it is less scattered and less absorbed than in the atmosphere).
Challenge (Clicking a Pest)
Shepherds are very effective at flipping the whip, However, for beginners this does not work. What makes a sound when they click a whip? (Two explanations are possible here: either the tip of the whip, bending, hits on its own, making a sound, or moving faster than the sound, it creates a shock wave),
Answer the following questions:
1) What is the reason for the sound? (Sound is caused by mechanical vibrations in an elastic medium and bodies whose frequencies lie in the range from 16 to 20,000 Hz and are perceived by the hearing organs).
2) What is a sound wave? (A sound wave is a sequence of contractions and
tensile elastic medium, propagating not instantly, but with a certain finite speed.)
3) What is the prerequisite for the emergence and propagation of sound? (A prerequisite for the emergence and propagation of sound. The presence of an elastic medium).
4) What is the source of fluctuations in the sound of people’s voices. (The source of fluctuations in the sound of people’s voices is their vocal cords).
4. Information about homework §§ 31-32 exercise 26 No. 2; Number 5
5. Reflection. voices of life.
Reflection Card
The face shines with happiness. It means "5". everything is clear!
You can already see by the face that “4”, not 5. You worked well, but there are still questions.
Do you frown? So "3", you do not blame anyone. Try to be in time yourself, do not yawn at lessons!