# Why the pitch of the circular saw goes down

## Four crests of waves passed by the motionless observer, standing on the shore of the lake, in 6 seconds. The distance between the first and third ridges is 12 m. Determine the period of oscillation of water particles, the speed of propagation of waves and their length. 2. (a) Why does the pitch of the circular saw decrease when the board is pressed against it? b) How does the length of a sound wave change when passing from air to water, if the speed of sound propagation in air is 340 m / s, and in water 1480 m / s? 3. Figure 21 shows a graph of the dependence of the speed of an oscillating body on time. At what moments in time is the kinetic energy of a body equal to zero? Find at least 2 values.

\ u0414 \ u043b \ u0438 \ u043d \ u0430 \ u0432 \ u043e \ u043b \ u043d \ u044b \ u0440 \ u0430 \ u0432 \ u043d \ u0430 12 \ / 2 = 6 \ u043c (\ u0442 \ u043c u0436 \ u0434 \ u0443 \ u0442 \ u0440 \ u0435 \ u0442 \ u044c \ u0438 \ u043c \ u0438 \ u043f \ u0435 \ u0440 \ u0432 \ u044b \ u043c \ u0433 \ u0440 \ u04d u0443 \ u043a \ u043b \ u0430 \ u0434 \ u044b \ u0432 \ u0430 \ u0435 \ u0442 \ u0441 \ u044f 2 \ u0432 \ u043e \ u043b \ u043d \ u044b) \ n

\ u0421 \ u043a \ u043e \ u0440 \ u043e \ u0441 \ u0442 \ u044c \ u0435 \ u0441 \ u0442 \ u044c \ u043e \ u0442 \ u043d \ u043e \ u0448 \ u0435 \ u038 \ u043 \ u0448 \ u0435 \ u038 \ u043d \ u0448 \ u0435 \ u038 \ u043d4 \ u044b \ u0432 \ u043e \ u043b \ u043d \ u044b \ u043a \ u043f \ u0435 \ u0440 \ u0438 \ u043e \ u0434 \ u0443: 6 \ / 1,5 = 4 \ u043c \ / \ u0441 \ n

\ u0430) \ u0414 \ u043e \ u0441 \ u043a \ u0430 \ u043f \ u0440 \ u0435 \ u043f \ u044f \ u0442 \ u0441 \ u0442 \ u0432 \ u0443 \ u0435 \ u0442 \ u040435 u0438 \ u044e, \ u0447 \ u0430 \ u0441 \ u0442 \ u043e \ u0442 \ u0430 \ u0432 \ u0440 \ u0430 \ u0449 \ u0435 \ u043d \ u0438 \ u044f \ u0443 \ u0354c \ u044f \ u0443 \ u0354c \ u354 \ u0442 \ u0441 \ u044f, \ u043f \ u043e \ u044d \ u0442 \ u043e \ u043c \ u0443 \ u0437 \ u0432 \ u0443 \ u043a \ u0441 \ u0442 \ u0430 \ u043f \ u043e \ u044d \ u0442 \ u043e \ u043c \ u0443 \ u0437 \ u0432 \ u0443 \ u043a \ u0441 \ u0442 \ u0430 \ u043 \ u04d \ u043e \ u441 u043d \ u0438 \ u0436 \ u0435 \ n

\ u0431) \ u0447 \ u0430 \ u0441 \ u0442 \ u043e \ u0442 \ u0430 \ u043f \ u0440 \ u0438 \ u043f \ u0435 \ u0440 \ u0435 \ u0445 \ u043e \ u0434 \ u0435 \ u043e \ u0434 \ u0435 \ u043e \ u0434 \ u0435 \ u0435 u044f \ u0435 \ u0442 \ u0441 \ u044f, \ u043f \ u043e \ u044d \ u0442 \ u043e \ u043c \ u0443 v1 \ / L1 = v2 \ / L2, L2 \ / L1 = v1 \ / v2 = 340 \ / 1480

0.23, \ u0434 \ u043b \ u0438 \ u043d \ u0430 \ u0443 \ u0432 \ u0435 \ u043b \ u0438 \ u0447 \ u0438 \ u0442 \ u0441 \ u044f \ u043f \ u043e \ u0447 \ u438 \ u044 u0430 \ u0437 \ u0430 “]” data-test = “answer-box-list”

The period is equal to the ratio of the observation time to the number of ridges: T = t / N = 6/4 = 1.5 s

The wavelength is 12/2 = 6m (since 2 waves fit between the third and first crests)

Velocity is the ratio of wavelength to period: 6 / 1.5 = 4m / s

a) The board prevents rotation, the speed decreases, so the sound becomes lower

b) the frequency does not change during the transition, therefore v1 / L1 = v2 / L2, L2 / L1 = v1 / v2 = 340/1480

## Alternating electric current. AC inductance. Ohm’s law for a serial section of a circuit. page 13

The speed of sound depends on the elastic properties, density and temperature of the medium. The greater the elastic forces, the faster the vibrations of the particles are transmitted to the neighboring particles and the faster the wave propagates. Therefore, the speed of sound in gases is lower than in liquids, and in liquids, as a rule, it is less than

in solids. For comparison, let us give the speed of sound in air, in water and in iron at / = 20 ° C:

The speed of sound in ideal gases increases with temperature as \ T (7 = 273 °-\-t° C is the absolute temperature). In air, the speed of sound is o = 331. at t = 0 °Cand v= 343. at t = 20 ° C. The speed of sound propagation in air was first determined in 1640 by the French physicist Maren Mersenne.

Sound waves (especially ultrasonic frequencies) are widely used in science and technology. For example, they are used to connect the smallest conductors in microelectronics, where traditional soldering is excluded, they are used in medicine for diagnostic purposes (the so-called ultrasound scanners, which allow examining the internal organs of a person. Unlike the radiation of X-ray machines, ultrasound radiation is harmless to humans).

The method of orientation or investigation of surrounding objects, based on the emission of ultrasonic pulses with the subsequent perception of the echo from them, is called echolocation, and the corresponding devices are called echolocators. The most famous animals with the ability to echolocate are bats and dolphins. In terms of their perfection, the sonars of these animals are not inferior, and in many respects are superior to modern man-made sonars.

| This way of orientation is possessed by various cetaceans, as well as guajaro birds nesting in deep caves in Venezuela and on the island of Trinidad, swifts-salagans living in caves in Southeast Asia.

Sonars used underwater are called sonars or sonars (name sonarformed from the initial letters of three English words: sound. sound, navigation.navigation, range. range). Sonars are indispensable for investigating the seabed (its profile, depth), for detecting and investigating various objects moving deep under water. With their help, both individual large objects or animals and schools of small fish or mollusks can be easily detected.

2 1. What is the nature of sound and its sources? ‘2. How sounds are classified?

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What range of sound frequencies does the human ear perceive??

What is the speed of sound propagation in air?

What are the frequencies of infrasound and ultrasound?

What are the main characteristics of sound.

What is the threshold of hearing? pain threshold?

At what frequency does the human ear have the best sensitivity??

Give examples of the use of sound waves.

Who flaps their wings more often in flight: a fly or a mosquito?

Why does the pitch of the circular saw go down when the board is pressed against it??

) / ^The exercise 36

The distance between the two railway stations is / = 8.3 km. How long does it take for a sound to travel from one station to another through the air and on rails? Air temperature f = 0 ° C. The speed of sound propagation in steel mouth =

\ / 2. Dolphins emit ultrasonic waves with a frequency

v = 250 kHz. Determine the wavelength A, such a sound in water and in air at a temperature of f = 20 ° C. 3. What is the depth of the sea H in a given place, if the ultrasonic pulse returned in At = 0.20 s after it was sent? Ultrasound speed in seawater and =

A person sees a heavy stone falling onto a concrete sidewalk. Some time later, he hears two sounds from the impact: one came through the air, and the other spread through the concrete. The time interval between them Af = = 1.2 s. At what distance / from the person the stone fell?

## Why, when fired from a gun, a bullet flies out with a whistle, and the thrown

Why, when fired from a gun, a bullet flies out with a whistle, and when thrown by a hand flies silently? Why does the pitch of the circular saw go down when the board is pressed against it??

Slide 7 from the presentation “Volume and pitch” to physics lessons on the topic “Sound”

Dimensions: 960 x 720 pixels, format: jpg. To download a free slide for use in a physics lesson, right-click on the image and click “Save Image As. “. You can download the entire presentation “Volume and pitch.ppt” in a zip-archive of 721 KB.

Sound Reflection. 1. What is the speed of sound in air? A. 300 m / s B. 340 m / s V. 440 m / s D. 500 m / s. Test “Sound. 3. The sound wave in the air is: Sound reflection. ” A. Increases B. Does not change C. Decreases D. Changes in waves. 2. How the speed of sound changes with decreasing density of the medium?

“The world of sound”. Application of sound waves: Ultrasounds and infrasounds play a very important role in the living world. The vibrations of the needle left a sound track on the roller. Biological acoustics deals with the issues of sound and ultrasonic communication of animals. Nature, endowing living beings with hearing, showed considerable ingenuity.

“Sound”. Frequency spectrum of sounds of musical instruments. Man lives in the world of sounds. The strongest fluctuations will be observed at the ends of the forks. Objectives: 1. Introduce the concept of sound waves. The mosquito flaps its wings 10,000 times per second! SOUND CHARACTERISTICS Volume. The lower end also oscillates at the same time. tuning fork leg.

“Ultrasound and Infrasound Physics”. General acoustics studies the issues of the origin, propagation and absorption of sound. Audibility diagram of sounds. Mo sosh 1. Sound is created by long-term periodic sound sources. Completed: student of grade 11 Gauk M.A. Among the periodic oscillations, harmonic oscillations play a very important role.

“Infrasound”. Then there was an indistinct series of dashes and dots, and then a distinct “I’m dying.” The organ can reproduce infrasound. Natural (resonant) frequencies of some parts of the human body. Many rushed to the exit. The specific impact of infrasound on humans prompted the idea to create an infrasound weapon.

“Sound characteristics”. A. in meters per second B. in seconds V. in hertz D. in meters. Sound volume Pitch Sound timbre. 6. What is the approximate speed of propagation of sound waves in the air? Answers: Why do we hear a flying mosquito, but no bird? Answer the questions. Lesson topic: The frequency of oscillation of the wings of insects and birds in flight, Hz.

## Presentation “Loudness and pitch” in physics. project, report

The presentation on the topic “Sound volume and pitch” can be downloaded absolutely free of charge on our website. Project subject: Physics. Colorful slides and illustrations will help you engage your classmates or audience. Use the player to view the content, or if you want to download the report. click on the corresponding text under the player. Presentation contains 12 slide (s).

## Presentation slides

What is sound? What are the reasons for the sound. What are the physical characteristics of the sound? Mechanical vibrations of what frequencies are called sound?

Why, when fired from a gun, a bullet flies out with a whistle, and when thrown by a hand flies silently?

Why does the pitch of the circular saw go down when the board is pressed against it??

Who flaps their wings more often in flight: a fly or a mosquito?

Which expression is always true: a) every sounding body vibrates; b) any oscillating body sounds. How will the volume of the sound change if the amplitude of the oscillations of its source is reduced? a) decrease; b) will increase; c) will not change. 3. What does the pitch of the sound depend on? a) vibration amplitudes; b) vibration frequencies; c) the speed of sound. 4. In what units is the sound volume measured? a) decibel; b) sleep; c) Hz. 5. What is the root tone? a) Quality that allows you to distinguish the sounds of some sources from the sounds of others; b) the highest frequency of a complex sound; c) the lowest frequency of a complex sound. Answers: 1a; 2a; 3b; 4b; 5c.

1) §35, 36, answer the questions for paragraphs. 2) (for those who want to get “5”) Answer the question: “What is the difference between a major and a minor from the point of view of physics?”.

## Lesson project “Sound, timbre, volume.

Selected for viewing document Lesson in physics in 9.doc

Physics lesson in the 9th grade “Loudness and pitch”

The purpose of the lesson: To study the basic characteristics of sound waves.

1. Educational. Cause an objective need for future activities; promote the acquisition of knowledge “Loudness and Pitch”.

2. Developing. Development of horizons, analytical skills, to promote the development of speech, thinking, cognitive and general working skills;

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3. Educational. Continue to develop skills in public speaking, information retrieval and methods of working with information.

Equipment: computer class, Digital educational resource “Pitch and timbre of sound. Sound volume ”from the Unified Collection of Educational Resources, tuning fork with a hammer, multimedia projector, digital educational materials, metal ruler, soundtracks by Chaliapin and Pavarotti.

Setting the goal of the lesson, motivation 6 min

Learning new material. 20 minutes

Loudness level and its effect on the human body.

Reflection and homework 4 min

Hello! Nice to see you in class again.

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Introductory word from the teacher: something from yourself.

We will repeat the material that will be useful to us today in the lesson (Slide 1).

Stage 3. Lesson goal setting, motivation

Now let’s do the following experiment.

Tuning Fork Experiment. Hit the tuning fork not hard, the second time hard.

How do these sounds differ?? (Student responses)

Loudness is the physiological characteristic of sound, and what is the physical characteristic associated with loudness? Think and write the answer on the worksheet.

Fragments of works by Chaliapin and Placido Domingo sound.

Why singers’ voices sound different? (Student responses)

Sound pitch. this is also a physiological characteristic. What is the physical characteristic responsible for the pitch? (Students’ answers (assumptions) are recorded on the worksheet.)

There is another characteristic of the sound called timbre. What do you think it is? (write your hypothesis on the worksheet)

What do you think is the topic of our lesson and its purpose? (Student responses). The topic of the lesson “Pitch and volume of sound” appears on the screen. (Slide 2)

(After 10 minutes, there is a check of work in pairs. The results of the work of pairs are heard.)

If there is no Internet access and computers, then the class is divided into 3 groups. Each group is given a card with a text to learn about one of the characteristics of sound, how to demonstrate them, and speak to the class. If the class is strong, then you can give the text from the textbook and choose the necessary tools for demonstration yourself, if not, then give the adapted text (below) and a ready-made set of tools.

Now let’s move on to discussing the characteristics of sound. The first is the pitch. Sound pitch. frequency characteristic. The higher the frequency of the body that vibrates, the higher the sound will be. Let’s go back to the ruler in a vice. As we said, we saw vibrations, but did not hear sound. If now the length of the ruler is made smaller, then we will hear the sound, but it will be much more difficult to see the vibrations. Take a look at the ruler. If we act on it now, we will not hear any sound, but we observe vibrations. If we shorten the ruler, we will hear a sound of a certain pitch. We can make the length of the ruler even shorter, then we will hear the sound of an even higher pitch (frequency). We can observe the same thing with tuning forks. If we take a large tuning fork (it is also called a demonstration tuning fork) and hit the legs of such a tuning fork, we can observe the vibration, but we will not hear the sound. If we take another tuning fork, then, hitting it, we will hear a certain sound. And the next tuning fork, a real tuning fork, is used to tune musical instruments. It emits a sound corresponding to the note A, or, as they say, 440 Hz.

The next characteristic is the timbre of the sound. Timbre called the color of the sound. How can this characteristic be illustrated? Timbre is what distinguishes two identical sounds played by different musical instruments. You all know that we have only seven notes. If we hear the same A note played on the violin and on the piano, then we will distinguish them. We can tell right away which instrument created this sound. It is this feature. the color of the sound. that characterizes the timbre. It must be said that the timbre depends on what sound vibrations are reproduced, except for the main tone. The fact is that arbitrary sound vibrations are quite complex. They are made up of a set of individual vibrations, they say Spectra vibrations. It is the reproduction of additional vibrations (overtones) that characterizes the beauty of the sound of this or that voice or instrument. Timbre is one of the main and brightest manifestations of sound.

Another characteristic is loudness. The volume of the sound depends on the amplitude of the vibrations. Let’s take a look and make sure that loudness is related to vibration amplitude. So let’s take a tuning fork. Let’s do the following: if you hit the tuning fork weakly, then the vibration amplitude will be small and the sound will be quiet. If now you hit the tuning fork harder, then the sound is much louder. This is due to the fact that the vibration amplitude will be much larger. The perception of sound is a subjective thing, it depends on what the hearing aid is, how a person feels.

Speeches of the guys. (Summary on slide 4)

Now let’s get back to your assumptions. In the worksheet, under the line, write down the correct answers to the question: what values ​​do the pitch and volume of the sound, timbre depend on? Raise your hands, who guessed right? Very good! (Students raise their hands)

You have metal rulers on your tables, with their help you get the highest sound and at the same frequency the loudest and quietest sound (students demonstrate).

In problem books, in passports of acoustic devices for their characteristics, instead of sound loudness, it is customary to use the loudness level measured in backgrounds or the level of sound pressure measured in bels and decibels. (Slide 4).

Let’s take a look at the table. What sounds create what level of sound pressure and how they affect the body with prolonged exposure. 40 decibels is considered the norm.

When comparing sounds of different frequencies, the following factor should be considered that affects loudness. The point is that the human ear is sensitive to different frequencies in different ways. Therefore, at the same amplitudes, we perceive sounds as louder, the frequency of which lies in the range from 1000 to 5000 Hz. The sound volume also depends on the duration of its sounding and on the individual characteristics of the listener. The following simple devices are used to amplify sound: horn, loudspeaker, phonograph.

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Let’s try to apply our knowledge, answer a number of questions.

Now let’s check your knowledge gained in this lesson.

How will the sound volume change if the amplitude of the oscillations of its source is reduced??

In what units is the sound volume measured??

a) quality that allows you to distinguish the sounds of some sources from the sounds of others;

b) the highest frequency of a complex sound;

Stage 6 Reflection and homework. (Slide 10)

For each letter of the word SOUND, name the association that arises in your lesson. (Student responses).

Paragraphs 35, 36, answer the questions under paragraphs.

(For those who want to get “5”) Answer the question: “What is the difference between a major and a minor from the point of view of physics?”.

Thank you for the lesson! It was a pleasure to work with you.

A.V. Peryshkin Physics. 9kl.: textbook for general education. institutions / Peryshkin A.V., E.M. Gutnik 13th ed., Rev M.: Bustard, 2008.

The sound selected for viewing. timbre, volume.ppt

## Solving problems “Mechanical vibrations and waves

Technological map of a physics lesson

Solving problems “Mechanical vibrations and waves”

Develop cadets’ understanding of sound and its characteristics.

### 11 WORST CIRCULAR SAW MISTAKES!! And How To Avoid them(DON’T DO THESE THINGS! Kickback/Binding)

Subject result: the formation of a scientific worldview, the formation of the ability to recognize sound phenomena and explain, on the basis of available knowledge, the basic properties and conditions of the occurrence of these phenomena, a description of the studied properties of the phenomena, using physical quantities: loudness, height, timbre, the formation of the ability to correctly interpret the physical meaning when describing phenomena used quantities

Metasubject result: development of the ability to generate ideas, identify cause-and-effect relationships, look for analogies and work in a team, use alternative sources of information, form the ability to analyze facts when observing and explaining phenomena, when working with the text of a textbook,

Personal result: the formation of skills to manage their educational activities, preparation for the awareness of the choice of a further educational trajectory, the formation of interest in physics in the analysis of physical phenomena, the formation of motivation by setting cognitive tasks, disclosing the connection between theory and experience, the development of attention, memory, logical and creative thinking; fostering a sense of pride in the country, humanism, a positive attitude to work, dedication (in the value-orientational sphere

Physics. 9th grade: textbook. For general education. institutions / A. V. Peryshkin, V. Gg. Gutnik. 14th ed., Stereotype M. Drofa, 2010. 192 p.: Silt.

Collection of problems in physics: 7-9 grades: to the textbooks of A. V. Peryshkin et al. “Physics. Grade 7 “,” Physics. Grade 8 “,” Physics. Grade 9 “/ A. V. Peryshkin; Compiled by N.V. Filonovich.-5th ed., Stereotype M.: Publishing house “Exam”, 2010 190,

Collection of problems in physics. 7-9 grades: a manual for general education students. institutions / V.I. Lukashik, E.V. Ivanova 24th ed M.: Education, 2010. 240 p.: ill.

Thematic and lesson planning in physics: Grade 9: To the textbook A. V. Peryshkin, V. G. Gutnik “Physics. Grade 9 “/ R.D. Minkova, E. N. Panaioti 2nd ed.-M.: Publishing house “Exam”, 2004.-127 p.: ill.

Check the readiness for the lesson, prepare the cadet for work in the lesson

Receives the report, greets the cadets, records the absent; checks the external condition of the classroom; checks the readiness of the cadets for the lesson; organizes attention and internal readiness for the lesson.

Submit a report. Prepare the workplace. Get ready for work.

Today we will continue the study of wave phenomena, but first we will repeat the previously studied material.

Some of the cadets will perform test work, and the rest will answer questions from the field.

In what medium can elastic shear waves propagate? Elastic longitudinal waves?

What is called wavelength? Write down the formula for finding the wavelength.

How long does it take for the oscillatory process to propagate over a distance equal to the wavelength?

What determines the speed of wave propagation?

Realization of personal life experience.

Sign-symbolic actions, including modeling.

Learning new knowledge and ways of doing things

Organizes independent problem solving

Analysis of objects in order to identify features.

Sign-symbolic actions, including modeling.

Establishing causal relationships.

Solving qualitative and quantitative problems

To do this, I propose to answer some questions:

What determines the volume and pitch of the sound? You must correctly insert the missing words and correctly characterize the sound depicted on the slide (loud or quiet, high or low). (Slide 12, 13; check with the “Listen” buttons).

Which expression is always true: 1) every sounding body vibrates; 2) does every oscillating body sound? (Slide 14).

3 could astronauts communicate on the moon using sound waves?

4.What kind of waves do sound waves belong to??

5 why bats don’t bump into obstacles even in total darkness?

In what sequence should the ranges of audible sound, infrasound and ultrasound be placed on the wave frequency scale??

7 why the pitch of the circular saw is lowered when the board is pressed against it?

8 why strings designed to create low sounds (bass) are braided with a spiral of wire?

Which insect: a mosquito or a fly flaps its wings more when flying? Why?

The knock is louder if you knock not on the wall, but on the door with the same force. Why?

Conscious and voluntary construction of a speech utterance in oral form.

Listening comprehension of students’ answers, the ability to formulate their own opinion and position, the ability to use speech to regulate their actions \

Monitoring the correctness of students’ answers.

Self-control of understanding questions and knowing the correct answers. Ability to listen in accordance with the target. Acceptance and preservation of educational goals and objectives. Clarification and addition of students’ statements.

Homework formulation, instructions on how to complete it

Homework: Review § 30-37; optional report “Sound Reflection. ECHO “.

Listening to the teacher and writing homework in a notebook.

Extraction of essential information from the teacher’s words.

Conducts reflection, analyzes the selected “faces”