Can sound travel through empty space? Let's find out by an experiment.

What you need:

Empty glass bottle with a cap, small bell, short firm wire, adhesive tape, matches, and paper

What you do:

  • Attach the bell to the piece of wire. Fix the opposite end of the wire to the inside of the bottle cap with tape. Check if the bell rings when you shake the wire.
  • Screw the cap onto the bottle. Shake the bottle to ensure that the bell jingles inside without touching the sides of the bottle.
  • Unscrew the cap. Tear the paper into shreds and drop the pieces into the bottle.
  • Light two matches and drop them into the bottle. As soon as you do this, quickly screw on the cap with the bell. (Take the help of an adult to do this step.)
  • Wait till the matches and the shredded paper burn out and the bottle cools.
  • Shake the bottle. Can you hear the bell?
  • Open the cap to let in some air and screw it on again. Shake the bottle again. Can you hear the bell now?

What do you observe?

You can hear the bell faintly immediately after the matches extinguish. After you open the cap and screw it on again, you can hear the bell ring louder.

Why does this happen?

Sound needs a medium like air or water to travel through. Sound waves vibrate the particles of the medium. When these vibrations reach our eardrums, we hear sound.

In the experiment, the burning paper and matches used up the oxygen in the sealed bottle, creating a partial vacuum. As sound cannot travel in a vacuum, you cannot hear the bell well until you let in some air into the bottle.

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HOW LONG CAN YOU LISTEN TO 120 DECIBELS?

Exposure to sounds at 120 decibels can damage your hearing in 7.5 minutes. Over 1.5 billion people globally live with hearing loss. According to the World Health Organisation (WHO), around 1.1 billion teenagers and young adults are at risk of developing hearing loss due to the unsafe use of personal audio devices, including smartphones, and exposure to damaging levels of sound at noisy entertainment venues such as nightclubs, bars and sporting events. World Hearing Day in on 3 March.

If you are curious as to just how loud 120 decibels is, you’ve come to the right place. In this article, we’re taking a closer look at this decibel level to see what it is equivalent to and how intense a 120 dB sound can get.

When we want to find out just how loud a sound is, we turn to the decibel scale to learn the answer. This scale runs from 0 dB, which is equivalent to the quietest sound a human can perceive and goes up to 140 dB, a sound level that can instantly cause hearing loss.120 decibels sounds like or is equivalent to the noise generated by:

  • a chainsaw
  • a thunderclap
  • a rock concert

As you can see, 120 dB is a very loud noise level, close to the upper limit of the decibel scale.

120 dB is a decibel level that describes extremely loud sounds. In fact, on a decibel chart, 120 dB marks the limit from which sounds become painful and very dangerous to the human ear.

To better understand how loud that is, here are more examples of what 120 dB of sound is equivalent to:

  • a loud alarm or siren such as an ambulance siren
  • a gunsho
  • an oxygen torch
  • a loud symphony
  • an aircraft takeoff
  • a Green Grocer Cicada
  • the sound made by some animals like the North American bullfrog or Northern elephant seals

It is important to note that 120 decibels is a noise level so extreme that it can instantly damage your hearing and being exposed to such loud noises for even a few seconds can cause irreversible hearing damage or hearing loss.

For the human ear, which is very sensitive especially to sound impulses, exposure to noise  levels above 85 decibels becomes dangerous after 8 hours and the recommended maximum exposure drops each time there is the slightest increase in decibel level.

Each time a sound’s level increases by 10 dB, its intensity also increases 10 times. This is because the decibel scale is logarithmic, not linear, and describes progressing measurement changes. So, even though we may think that a 10 dB sound difference is negligible, it is, in fact, quite significant.

Exposure to sounds below 70 decibels is considered safe for human hearing no matter how long you are exposed to this level. This limit is considered for adults. For babies, the maximum decibel level they should be exposed to is 50-60 dB.

Credit : Decibel pro

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Which sound is called noise?


Rattling trucks, roaring jets, squeaking chalk, and creaking doors don’t make music. They make sounds that disturb us - sounds we don’t want to hear. These unwanted sounds are called noise.



Noise is hard to stop. Like other sounds, noise travels through air and through solid things - even through walls.



But some materials actually soak up noise. They absorb sound waves and keep them from travelling. Inside a building, rugs and curtains soak up sound. The soft threads and tiny air spaces in the material help trap the vibrations. Special ceiling tiles can trap sound vibrations, too. The tiles are full of tiny holes, like a sponge. When sound waves strike the tiles, they bounce around inside the holes until they get weaker and die away.



People who work with aeroplanes and other heavy machines wear special helmets and earmuffs to cover their ears while they are working. The sound-absorbing material shuts out most of the noise that could bother them or even hurt their ears.



There is a special branch of science that deals with the way sound affects people. This science is known as acoustics. Acoustics helps people design theatres so that music sounds good. It also helps them work out how to control harmful noise. Scientists even use acoustics to study how we make and understand sounds.



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How can we measure the intensity of sound?


Sounds can be high or low. But they can also be loud or soft. What makes a sound loud or soft?



Sounds are the vibrations, or back-and-forth movements, made by moving objects. Strong vibrations make strong sounds. Vibrations are strong when an object moves a lot.



You can make a sound by stretching a thick rubber band and then plucking it with your fingers. If you pluck the rubber band hard, the back-and-forth movements are bigger. Bigger movements make a louder sound. If you pluck the rubber band lightly, the back-and-forth movements are smaller. So the sound is softer.



Scientists measure the strength of a sound in units called decibels. A sound of zero decibels is the weakest sound a person with normal hearing can hear. A sound of 140 decibels hurts your ears.



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What are reflected sounds?


What happens when you shout a big “hello” near a mountain, or between tall buildings, or in a large, empty hall? Well, you may hear an echo, another “hello” just like the one you shouted.



Sound bounces off hard, smooth things the way a ball bounces off a wall. The echo of your “hello” is reflected sound - sound that bounces back to you.



Why don’t you always hear echoes? It depends on how far the sound goes before it bounces. In a small room, the sound you make travels only a short distance before it bounces. It comes back so fast that it seems like part of what you are saying.



But in a very large room, the sound travels a while before it bounces back. By the time the sound comes back, you have finished speaking. So you hear the sound a second time.



You can hear the sound you make again, and again, and again! For example, if you shout between two tall buildings, the sound bounces back and forth between the walls. When that happens, the sound is reflected back to you from more than one spot. You hear “hello . . . hello . . . hello . . .” from each reflected sound. As the reflections get weaker and weaker, the sound dies out and the echoes finally stop.



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Why does there a change in the whistle of train when it rushes by?


Have you ever noticed a change in the “whistle” a train makes as it rushes by? If you listen to a passing train, you’ll notice that the sound gets higher and then lower as the train goes past you.



Actually, the whistle makes the same sound all the time. The sound seems to change because the train is passing you.



The sound spreads out in all directions from the train. But because the train is moving, each sound wave starts a little ahead of the place where the last one started. This makes the sound waves ahead of the train bunch up so that more of the waves reach your ear every second. And the more waves that reach your ear in a second, the higher the sound.



But behind the train, the waves are spread apart. As the train speeds away, fewer waves reach your ear each second - so the sound gets lower.



Most things never catch up with the sound waves they make. But some jet planes do. Supersonic planes can fly faster than sound travels. When they fly this fast, they slam into the waves of air they have made. This creates a tremendous air wave called a shock wave. The shock wave spreads out behind the plane in a funnel shape. Travelling at the speed of sound, the shock wave crashes into the air and the ground. This makes a huge exploding noise called a sonic boom.




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Why are the sounds different?


Zzzeee goes the tiny mosquito as it zips past your ear. VROOOM growls a big tractor as it rumbles past you. The sound the mosquito makes is much higher than the sound of the tractor. When something vibrates, sound travels outwards from it in waves. Each vibration - each complete back-and-forth motion - makes a single sound wave. The faster something vibrates, the more sound waves it makes and the higher the pitch.



A mosquito makes high-pitched sounds because its wings vibrate very fast - about a thousand times a second!



A tractor makes low-pitched sounds because its heavy metal parts vibrate slowly. The slow vibrations make only a few sound waves every second - the low rumble that you hear.



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Why does the ticking sound of clock get softer when we walk away from the clock?


A ticking clock sounds loud when you put your ear close to it. As you walk away, the ticking gets softer and softer, until you can’t hear the ticking at all.



The ticking you hear is made by the moving parts of the clock. The movement of these parts - the tiny pushes and pulls - makes the air around the clock move. It pushes the air molecules together into sound waves.



The sound waves from the clock spread out in all directions. They move through the air to your ear, and you hear the ticking.



The sound waves are strongest at the point where they are made - close to the vibrating clock. So when you stand next to the clock, the ticking is loud. But as the sound waves spread out through the air, they grow weaker and weaker. So as you move away from the clock, the ticking gets softer.



By the time the sound waves have travelled across the room, the air is hardly moving at all. The pushes and pulls are too tiny for your ears to pick up, so you no longer hear the sound of the ticking clock.



Picture Credit : Google


Does sound travel through liquids or solids?


A swimming fish seems to glide through the water without making a sound. But it doesn’t swim as quietly as you think. Divers swimming underwater hear a loud crack when a large fish flips its tail and darts away.



Most of the everyday sounds we hear travel through air. But sound waves travel through liquids and solids, too. Things like water, wood, and even the earth can conduct, or carry, these vibrations. You know this is true if you’ve ever heard noise coming from a closed room. Sound travels through walls and doors.



The molecules of liquids and solids are closer together than the molecules in air. And in some liquids and solids, the molecules are “springy”. They bounce back like a rubber band when they are pushed.



These kinds of molecules vibrate easily when a sound wave pushes them. And they make nearby molecules vibrate, too. So in a solid or liquid with “springy” molecules, sound travels even faster than it travels through air.



A loud sound takes about 5 seconds to reach you if it travels 1.5 kilometres through air. But underwater, the same sound reaches you in little more than a second. And a sound wave zips through 1.5 kilometres of steel wire in about 1/3 second. This is almost 15 times faster than it travels through air.



Picture Credit : Google


How does Recording happen?


RECORDING



 To record sound, the pattern of vibrations in the air must be turned into a form that can be stored. The gramophone was the first sound-recording device. To record, the sound was made to vibrate a needle, which cut a wavy groove in a foil surface. To play back, the needle moved along the groove, making a diaphragm vibrate to reproduce the sound. In the electric gramophone, introduced in the 1920s, the vibrating needle created an electrical signal, which was amplified to drive a loudspeaker.



The first type of gramophone was the phonograph, invented in 1877 by the American inventor Thomas Edison.



Tape recording was developed in the 1940s. To record on to tape, the electrical signal from a microphone is sent to an electromagnet, which creates a pattern in the tiny magnetic particles that coat the tape. This pattern recreates the signal as the tape plays, and the signal is amplified before going to a speaker.



Most sound recording is now done digitally. A microphone turns the sound into an analogue electrical signal, which is then digitized more than 44,000 times a second to create a long string of binary numbers. The binary numbers can be stored in a computer’s memory or disc drives, or on a compact disc (CD). On a CD, the binary digits 0 and 1 are represented by flat areas or shallow pits in the surface. In a CD player, these are detected by a laser as the disc spins and reflected to a light-sensitive device. Electronics rebuild the original electric signal, which is amplified and sent to speakers. Computer CD-ROMs and DVDs work in the same way.




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How would you distinguish between Pitch and Volume of Sound?


PITCH AND VOLUME



Sound has two important features. One is pitch. A low-pitched sound is deep, like a roll of thunder or a booming big drum. A high-pitched sound is shrill, like a snake’s hiss or the tinkle of a triangle. Pitch depends on the frequency of sound waves - the number of waves per second. High-pitched sounds have high frequencies.



Some sounds are so high-pitched that our ears cannot detect them. They are known as ultrasounds. Many animals, like dogs and bats, can hear ultrasounds.



The second important feature of sound is its loudness or volume. Some sounds are so quiet that we can only just hear them, like a ticking watch or the rustling of leaves. Other sounds are so loud, like the roar of engines or the powerful music in a disco, that they may damage the ears. Sound volume, or intensity, is measured in units called decibels (dB). Sounds of more than 80-90 decibels can damage our hearing.



            An ultrasound scanner beams very high-pitched sound waves into the body. The echoes are analyzed by a computer to form an image, the baby in the womb.



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What do you know about Sound?


SOUND



One of the most familiar forms of energy in daily life is sound. We hear natural sounds like birdsong and wind. We hear the noise of vehicles and machines, and sounds such as speech and music from radios, televisions and stereo systems. We also rely on sounds to communicate when we talk to others.



Sounds are made by objects that vibrate (move to and fro rapidly). As an object vibrates, it alternately pushes and pulls at the air around it. The air is squashed and stretched as the molecules of the gases in air are pressed close together and then pulled farther apart. These are regions of high and low air pressure. They pass outwards away from the object in all directions. They are called sound waves.



Sound waves start as the energy of movement in the vibrations. This is transferred to the energy of movement in air molecules. As the sound waves spread out they widen and disperse, like the ripples on a pond after a stone is thrown in. So the sound gradually gets weaker and fades away. However if there is a hard, smooth surface in the way, such as a wall, then some sound waves bounce off it and come back again. The bouncing is known as reflection and we hear the returning sound as an echo.



Sounds also travel as vibrations through liquids, such as water, and solids, such as metals. The atoms or molecules are closer together in liquids than in air, and even closer still in solids. So sounds travel through them much faster.



            An object that vibrates to produce sound waves is a sound source. A bow rubs over the cello’s string and makes it vibrate. The vibrations pass into the air and also to the cello’s hollow body making the sound louder and richer.



The speed of sound varies depending on the substance it travels through. Atoms in steel are closer than molecules in air, so the vibrations of sound move faster and further.



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Can sound hurt?


 



 



             The loudness of sounds is measured in units called decibels (dB).Ordinary speech has a sound intensity of about 20 decibels, while a noisy room full of people produces about 70 decibels. The quietest sound you can hear is about 20 decibels. Loud music at a rock concert reaches a level of about 125 decibels, while sounds of 140 decibels or more actually cause pain in the ear. This level of sound can produce permanent hearing damage if it continues, which is why people operating noisy machinery have to wear ear protectors.




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How can sound detect submarines?


         



                Sound waves travel very well through water, so they are used to detect submarines or even shoals of fish. A sonar device under a ship sends out sound waves that travel down through the water. The sound waves are reflected back from any solid object they reach, such as a submarine, shoals of fish or the seabed. The echoes are received by the ship and can be used to ‘draw’ an image of the object, and its location, on a screen.



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What causes thunder?


 



               Thunder is produced when lightning heats up the surrounding air very rapidly, causing it to expand faster than the speed of sound. This produces a ‘sonic boom’ like the one caused by a supersonic aircraft. If you count the seconds between seeing a flash of lightning and hearing thunder and divide this number by 3, it will tell you how many kilometres away from the lightning you are. Sound travels at about 1220 km/h, while light from the lighting strike travels so fast that you see it almost instantaneously.




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