Sound Answers

by Deb on February 22, 2012

Sound

Somehow I had a scheduling glitch and the answers to the Sound quiz were never posted. Here they are, better late than never.

1.     The loudest animal in the world is the Sperm whale, whose sonar clicks are about 230 decibels. Unfortunately sound works differently in the water and on land, so we can’t compare that to something we know without getting really complicated.

Sperm whales don’t sing like blue and humpback whales, instead they are toothed whales related to dolphins and use their clicks to hunt in the black ocean depths. Light only reaches down around 200m but sperm whales hunt squid in canyons twice that deep, their loud sonar helps them to locate their prey.

Sperm whales are named from their spermaceti, an oily or waxy substance found in hollow bones on the top and front of their head above their jaw. This was almost the cause of their extinction, as they were hunted in part for their spermaceti which was used in candles, soaps, cosmetics and machine oils. Most of these have been replaced with synthetic or mineral oils – natural is not always better! It seems that the spermaceti is important in focusing the clicking noises onto a lens and helps make them so loud.

2.     Sound travels as waves of pressure through the air or water. Sounds come from movements, like your lungs and throat moving air or and object falling. As it moves it pushes the air molecules in front of it. They run into other molecules and push them before they bounce back. Eventually the air is pushed into your ear and pushes on your ear drum.

This is why sounds get quieter as you are further away – the air molecules bouncing off each other are using up some of their energy and are pushing the next molecules less and less, making the sound quieter and quieter.

3.     Beats occur because sound waves can add and subtract. If two sounds are pushing the air molecules forwards at the same time, they’ll get extra energy and move more, making the noise louder. But if one sound wave pushes forwards while another is pushing back, they’ll cancel out and the sound will be very quiet. This makes the volume go rhythmically up and down, called beating.

Beats are used to tune instruments, they help you tell when two very similar tones are at the same pitch because the beats stop. Watch the video at the end to hear some beats.

4.     The human hearing range typically goes from 20 Hz to 20 000 Hz but it is individual and varies with age. The upper ranges begin to be lost from as young as 8 years old. Women generally hear high frequencies better.

Many other animals have different hearing ranges, the best known are bats and dogs, who can hear much higher sounds giving us ‘silent’ dog whistles. Humans have a relatively low hearing range, many animals cannot hear as low as we can although elephants and ferrets can hear marginally lower. We can also sense lower sounds by feeling their vibrations.

5.     The plane in the picture has just broken the sound barrier. Originally this really was a barrier – as planes got faster and faster there was increasing turbulence and pressure and many people thought it would be impossible to get through. However they did, and on the other side there is not only smoothness (and quiet!) but a sudden drop of pressure. That’s what caused the amazing picture – the low pressure systems formed by the plane have decreased the temperature and caused water vapour to condense and form clouds.

Going faster than the speed of sound also causes the famous ‘sonic booms.’ Like beats, this is because sound waves add together. Planes send sound waves in all directions, including in front of them. As the plane gets faster and faster it ‘catches up’ with the sound waves ahead of it. All the sound waves pile on top of each other, creating a loud boom.

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