Sound and Pressure - No Fysik PDF

**No Fysik** **6.1** **Sound and pressure** **Acoustics** [is the study of sound]. We humans hear sound, but there are some sounds that we cannot hear. For example, we know that mice sing much like birds, but we cannot hear the mice\'s song. We also cannot hear the sounds that bats emit to orient...

**No Fysik** **6.1** **Sound and pressure** **Acoustics** [is the study of sound]. We humans hear sound, but there are some sounds that we cannot hear. For example, we know that mice sing much like birds, but we cannot hear the mice\'s song. We also cannot hear the sounds that bats emit to orient themselves in the dark. **Sound** [is produced when we speak, sing and scratch our noses]. Sound is produced by machines, ships, musical instruments, nutcrackers and brooms. Sound is produced by wind, water, thunder and the northern lights. Bild: Illustration. En vibrerande linjal Imagine a ruler that is hanging over the edge of a table. You snap the ruler and it starts to vibrate. The ruler pushes the molecules in the air over and over again. The molecules gain momentum and collide with other molecules. This causes them to oscillate back and forth. A pressure wave is formed in the air and spreads. This pressure wave reaches your ear and sets your eardrum in motion. At the faintest sound you can hear, your eardrum only oscillates back and forth by a ten-millionth of a millimeter. Further into the ear, the pressure wave is converted into an electrical signal. When the signal reaches your brain, you perceive the sound. **Sound** can only exist in matter. In a vacuum there is **no sound**. In movies about space wars you can sometimes hear the bangs of terrible explosions. That is completely impossible. Out in space it is soundless. Sound in a vacuum **Hearing** We hear with our brains. Our ears pick up sound waves, but it is the brain that interprets the sounds and createseaning. Something honks and the pressure wave sets the eardrum in motion. The vibration is conducted from the eardrum through the three auditory bones and reaches the cochlea in the inner ear. There, the movement is converted into an electrical signal that is sent to the auditory center in the brain for interpretation. "Something honks," the brain interprets. If we are to hear well, the pressure in the ear must be the same as the pressure in the environment. The pressure equalization occurs through the eustachian tube, which leads to the nose and throat.  The sound waves are captured by the outer part of the ear, the pinna, and are gradually converted into electrical nerve signals that the brain processes. The brain perceives a "meow." The sound is previously learned as a cat sound. The brain also perceives the very small difference in distance traveled by the sound. It reaches the person's right ear a microsecond earlier, which must mean that the cat is on the right. **Speed of sound** Sound travels at different speeds in different materials. In air, the pressure wave travels at a speed of 340 m/s. In water, the molecules are closer together and have an easier time pushing each other. Sound travels much faster in water. Imagine the sound of a motorboat spreading out in all directions. You may not hear anything when you are swimming, but if you dive underwater you can hear the sound of the engine. This means that the sound has not yet reached the air. In metals, sound travels even faster. In aluminum and iron, the speed of sound is 5,000 m/s.  If you lie sunbathing on the beach with your ear to the sand, you can hear the hooves even if the horse is far away. **6.2** **Audio sounds different** **Sound can be drawn** Sound is often drawn as a wave motion. Where the air is dense, you draw a peak and where it is thin, you draw a valley. Then it looks like this: Bild: Ljudvåg Sound waves oscillate at different speeds. An important thing to find out about all types of oscillations is **the frequency** . Frequency means how many oscillations the wave makes in one second. The unit for frequency is **1 hertz** (1 Hz). The wave above has five peaks and five troughs in one second. Then the frequency is 5 Hz.  The **oscilloscope screen** here shows an image of a tone. The sound has been converted into an electrical signal. **High and low tone** A high note has a high frequency and a low note has a low frequency. If you take a high note and hold your finger on your larynx, you can feel your vocal cords vibrating rapidly. Then take a low note and compare. Bild: Kurva, hög ton, hög frekvens **High pitch -- high frequency.**  **Low tone -- low frequency.** Note that the tones in the figures have the same strength. **Strong and weak tone** You can get different loud tones by plucking a guitar string with different force or blowing with different force on a flute. A loud tone has a very strong compression. A high peak is drawn to show that there is a lot of pressure. Bild: Kurva, stark ton, kraftig svängning **Strong tone -- strong oscillation.**  **Weak tone -- small oscillation.** Note that the figures show the same tone. Bild: Tvärflöjts-spelare. The length of the air column determines the tone you get in the flute. **Some sounds are noise** When you hear a tone, you probably think the sound is beautiful and harmonious. A tone is a smooth oscillation. You probably think it is pleasant to swing on a regular swing that swings smoothly and nicely. Riding on an uneven and shaky road is not pleasant. For the same reason, we don\'t like **noise** because it is an uneven oscillation.  **Noise is an uneven oscillation.** **Fundamental and overtone** In music, notes are usually written with notes and letters. You could just as easily write them with numbers. The frequency tells you what note it is. A tuning fork with the note single-barred a (a ^1^ ) is used by piano tuners. That note has a frequency of 440 Hz. This is what the tone with the frequency 440 Hz sounds like. If you first play the note a ^1^ on the piano and then play the same note on a guitar, it doesn\'t sound the same. It\'s the same note with the same frequency, but the string also produces **overtones** . It\'s the overtones that make your voice sound different from everyone else\'s, even if you sing the same note. Your voice is unique because no one else has the same overtones in their voice that you do. Bild: Kurvor för, stämgaffel, violin, flöjt, klarinett, vokalen A, vokalen O Same fundamental but different overtones. Note that there are four peaks in all the figures.  The standard C major scale. **Resonance** Two people in the class can hold a guitar string between them. When you pluck it, you won\'t hear much. However, if you pluck the string on the acoustic guitar where it belongs, you will hear the note clearly. The hollow space of the guitar causes the entire guitar to vibrate, amplifying the tone. This is called **resonance** . It is resonance that makes the music heard in an entire hall. The entire piano vibrates. The air in the violin and in the acoustic guitar vibrates. It is good if an opera singer has a large head. Behind the forehead there is then a good resonance box. On some roads there is a grooved center line or edge line. The whole tire starts to sing if you drive onto it. It is supposed to wake the driver if he falls asleep at the wheel and is about to drive into a ditch. Bild: Bilar på motorväg Anyone driving over the edge line is "awakened" by a tone. The grooved line produces a vibration. The sound is amplified by the resonance in the tire. **6.3** **Sound that is not heard** Sound is created when something vibrates. Fortunately, we don\'t hear everything. It would be a pain to constantly hear our own blinking and movements in our esophagus. We humans can only hear sounds between 20 Hz and 20,000 Hz. As we get older, our hearing deteriorates. It then becomes more difficult for us to hear soft sounds and even sounds with high frequencies. Many older people, for example, cannot hear crickets and grasshoppers.  **As we get older, our hearing deteriorates and we may have difficulty hearing grasshoppers that emit sounds above 10,000 Hz.** **Infrasound** **Infrasound** is sound with a frequency below 20 Hz. Power plants and large machines produce infrasound. Infrasound is also produced by wind and water in nature. A weather front moving towards us has an inaudible sound wave ahead of it. It is just like a boat having a bow wave ahead of it. We cannot hear the weather front approaching, but some people say that they get headaches when the weather is about to change. Many animals hear better than we do. They can hear both weaker sounds and sounds that are below or above the human hearing threshold. In the tsunami off Southeast Asia in 2004, many people died. In a national park in Sri Lanka, all the animals survived even though the wave penetrated three kilometers inland. There were elephants, leopards, buffaloes and many other animals. Perhaps the animals felt the shaking in the ground or heard the wave coming. We know that elephants can talk to each other over long distances using infrasound. **Ultrasound** **Ultrasound** is sound with a frequency above 20,000 Hz. We humans cannot hear that either. Birds and bats are known to be able to hear ultrasound up to very high frequencies. Dogs also hear ultrasound. With an ultrasonic whistle, we can whistle at the dog without disturbing the neighbor. Ultrasound is now widely used in medicine, for example to examine the heart and blood vessels and to treat stiff joints. Everyone who is expecting a baby receives an ultrasound examination of the fetus. The sound is converted into an image on a screen and the parents receive the first photo of the baby to take home. Ultrasound has many uses. With ultrasound we can clean delicate old fabrics, check welds, lock the car, turn off the TV and much more. Bild: Bild från 3D ultraljud. An image of the expected baby. All pregnant women are offered an ultrasound examination. A 3D ultrasound constructs a three-dimensional image of the fetus. **6.4** **Sound that damages** **Noise** Someone is scratching with a pen or scraping with a chair. A crane is dripping, a bus is thundering past, an airplane is coming in for landing. All of these are disturbing sounds and are usually called noise. Noise does not have to be loud sounds, but noise is always an irregular oscillation. We now know that the brain is affected by noise. What we learn in a noisy environment is much less memorable. Noise can cause stress and anxiety, which affects both humans and animals. Minks can become so stressed that they bite their young to death if an airplane flies low over them. **Sound level** To deal with noise in industry or traffic, **the sound level** is measured. The unit is **1 decibel** (1 dB). The scale is made so that the weakest sound a human can hear is 0 dB. A whisper is 30 dB. The fact that the sound level has increased by 10 dB means that we perceive the sound as twice as loud. **Damage to humans** Noise and loud sounds can cause permanent damage to the ear. Musicians often have major problems with hearing damage. A loud sound just once can cause damage so that you always hear a hissing or piercing sound in your ear. This is called **tinnitus** . Young children have particularly delicate eardrums. They should not use headphones or earbuds if they are listening to recorded stories before the age of two. Infrasound can also harm us. We become stressed and irritated and can have sleep problems. Tests show that infrasound can cause dizziness and nausea and even cause seizures. We don\'t know exactly how different organs in the body are affected. In some cases, infrasound can cause hallucinations. There are theories that this is what has happened when someone has seen ghosts.  A loud sound close to the ear can cause permanent hearing damage. **6.5** **Bullerbekämpning** Bild: Arbetare på fabrik med hörselskydd. Anyone working in a noisy environment must be careful to use the best possible hearing protection. For noise to be a problem, three things are required: - Something will make noise. - The sound must spread. - There must be someone who hears the sound. Traffic is often mentioned as a noise problem. To reduce the problem, cars and motorcycles are equipped with mufflers. Highways and airports are built outside cities. Other efforts to reduce traffic noise can include building noise barriers between roads and houses. In industries, machines should have sound-absorbing hoods to reduce noise. Machines and engines should be oiled so that they run as quietly as possible. If you work in a noisy environment, you should be careful about hearing protection. There are small soft plugs that can be purchased at the pharmacy. You can also get plugs that are molded to your own ear. If you drill, grind, compete in shooting or do anything else that produces sharp sounds, you should use earmuffs. At preschool it can also be noisy sometimes. It\'s not exactly possible to put up noise barriers around the children. The only option there is to be very careful when building the house. The floor should not be cast in a single slab. This will lead the sound between the rooms. There should be good insulation in the interior walls. The ceilings should have slabs with small holes so that the sound doesn\'t bounce around too much. The walls shouldn\'t be made of too hard a material either. The environment in all workplaces should be as good as possible in terms of noise. The person who is responsible for monitoring the work environment in a workplace is called a safety representative. You can also reduce noise at home. In the kitchen, the refrigerator should be as flat as possible so that it does not vibrate. **6.6** **Sustainable development -- ​​Noise and disturbing sounds** **Noise and disturbing sounds** In the sense of physics, noise is an irregular oscillation and tone is a regular oscillation. In densely built-up environments, it makes more sense to talk about disturbing sounds than about noise. Disturbing sounds can come from traffic, lawnmowers and construction work, things that everyone thinks are noise. Disturbing sounds can also be dogs barking, children screaming and newspaper rustling, things that are really noise in the sense of physics, but which are not usually called environmental problems. Disturbing sounds also include music that you don\'t like or music that is played at the wrong time, e.g. when you want to sleep. Noise and unwanted sounds are often cited as causes of stress and sleep problems. We are also becoming increasingly aware that disturbing sounds can cause lack of concentration and learning difficulties at school. We also know that sounds that we cannot hear, called infrasound, affect us. **Approximately one million adults are bothered by traffic noise** In a national environmental health survey in connection with the work on environmental goals, 14% of adults stated that they were bothered by traffic noise in their homes at least once a week. This is an increase from 12% eight years earlier. The increase is due to increased noise from road traffic. Noise from air and train traffic, on the other hand, has decreased. In a similar environmental health survey of families with children, it was found that 20% of 12-year-olds were bothered by noise in or near their home and/or school. Community noise is a widespread environmental problem and the environmental disturbance that affects the largest number of people in Sweden. The environmental quality objective Good built environment means, among other things, that the living environment should be healthy. In this case, it is very important that disturbing noise is limited if possible. In 1997, the Riksdag decided on guideline values for traffic noise and Sweden\'s municipalities adopt action plans for measures against noise. If little is done, today\'s social development will lead to a noise environment that is not consistent with the goal of a healthy environment throughout the country. **Irregular oscillation but not disturbing** There are also sounds that are noise in the sense of physics, but are still not disturbing. One can think of the rustle of the wind in the trees or the roar of the sea. How long the noise lasts is also of great importance. It may not be difficult to put up with a train passing every two hours, but it is much more difficult to endure a constant stream of cars outside your home.  Environmental goals Good built environment \"Cities, urban areas and other built environments should constitute a good and healthy living environment and contribute to a good regional and global environment. Natural and cultural values should be preserved and developed. Buildings and facilities should be located and designed in an environmentally friendly manner and so that long-term good management of land, water and other resources is promoted.\" Bild: Miljömål.