light and sound
Outline
- sound is vibration heard
- speed affects sound perception
- frequency varies with volume
- frequency varies with motion
- radio waves are vibrating electrons
- colour varies with light frequency
- colour reflected is colour detected
- light and sound are forms of energy
- light and sound can be absorbed or reflected
sound is vibration heard
Tin-Cans, My True Voice, and Rocks Music
The chatter of garage sales is a sound of summer. Karl and Lark, neighbours of Clay and Lacy, host the neighbourhood sale each year, combining the goods of everyone on the block into one site.
There is a lot to see. Clay and Lacy are drawn to anything retro. Last year, Clay found a lava lamp. Lacy picked up a classic wooden yo-yo. This year they found a tin can telephone, tape recorder, and ukulele.
The telephone is two soup cans at either end of a long chord. It works when the chord is pulled taut. When Lacy talks, her vocal cords vibrate to make air to vibrate. Talking into the can passes her message along the vibrating chord.
Using the old reel-to-reel tape recorder, Clay captured Lacy singing. She says the play-back doesn’t sound like her, although Clay thinks it does.
LACY
It sounds better in my head.
She isn’t wrong. The sound of Lacy’s voice is conducted through bones in her head. Bones enhance the low frequencies and—to her—add to the fullness of her voice. The tape recording is how she sounds to everyone else.
The recording picked up shuffling and coughing—background noise we tend not to hear when listening live. The recorder’s microphone does not have directionality of speech, so it picks up all ambient sounds.
In conversation, voices are directed toward one another rather than spreading out. That’s a little like a megaphone. The opposite is a foghorn: sound spread all around to warn ships from any direction.
It used to be that every school had a set of these, Clay says, picking up the plywood ukulele and strumming across its four nylon strings. I never knew when it was noise. Like bagpipes, he adds, and they laugh.
LACY
If it has a beat, it’s music.
CLAY
But that could be true of banging rocks together, faster or slower, harder or softer. I could play a rock song with rocks. We will, we will rock you.
Any elastic substance (such as water, metal, crystal) can transmit sound. Rocks are elastic. They vibrate and give off a sound. Car wrenches, big and small, give off different frequencies.
CLAY
I could play a song by tossing wrenches on the garage floor if I knew the timing.
LACY
Or you could hang different size wrenches on strings and play them by tapping with a metal rod. Like musical chimes, or a kind of xylophone.
But you won’t rock anyone with this, Clay says, picking up a package of plasticine. Modelling clay doesn’t vibrate, so no frequency.
According to Lacy, Ajay snores in rhythm. Snore in, whistle out. One day, he might snore out the national anthem. Just as likely, says Clay, is me playing the national anthem with this. He replaces the ukulele on the table.
speed affects sound perception
Sonic Snap, False Falsetto, and Shower Song
Alan arrived at the garage sale with a box of items on his bicycle carrier. Look at this, said Lacy, taking a whip from the box. Totally retro.
CLAY
That the one from the carnival?
ALAN
Yes, and be careful. The tip snaps at supersonic speed, like the sonic boom of a jet.
CLAY
I can make a towel snap like that. Kids do it in gym class. Roll a damp towel along an angle, like a croissant, then snap it.
Sound is fast. It is as fast as running the full length of a soccer field, running all the way back, and running to the end again—all in one second. For the tip to snap, it has to be faster than that.
Towel snapping is one of those do-not-do-this things, like inhaling helium for a false falsetto voice. The hazard is that helium prevents oxygen from getting to the brain, so use your brain when doing it.
After inhaling helium gas, a person has a high-pitched cartoon voice since sound, such as voice, travels faster in helium. Almost three times faster. The faster the speed, the higher the pitch.
CLAY
Helium makes my voice higher; a shower makes it sound lower.
Shower tiles don’t absorb sound, so Clay’s voice bounces around, sounding louder and deeper. The close walls echo back his voice in sync with his singing for a rich, deep voice.
Lacy picks up an old slate chalkboard and a thick stick of chalk and she slowly slides the chalk down the board. It squeaks, like an irritating fingernail on a chalkboard.
The chalk first sticks on the board, then suddenly slips and vibrates to make the screech. As the vibrations decrease, the friction between the chalk and board increases until the chalk sticks once again. This is similar to why doors creak or the tires on a dragster squeal on a quick start.
ALAN
Chalk squeak is right up there on my irritation list, along with the buzz of mosquito wings.
frequency varies with volume
Glug Jug, Playing Pops, and Scratch Sound
As Clay pours soda pop out of a bottle, it makes a glug, glug, glug sound.
ALAN
Pour me some. I think the glug sound goes up as you pour out more.
Clay poured, but the pitch went lower. It isn’t the pop that vibrates, but the air in the bottle. The more the air in the bottle, the lower the frequency of the glug sound. As Clay pours out soda pop, air takes its place in the bottle. More air, lower pitch.
The greater the volume of air, the lower the frequency. More air, lower glug, glug. Likewise, large organ pipes produce low notes. Some bottles start the glug, glug sound even before any liquid pours out.
Some sounds can make a person sick. That isn’t likely by blowing across a pop bottle, but the drone from driving could induce car sickness. The human body contains a lot of water and sound can vibrate liquids. Frequencies below the threshold of human hearing can cause vibrations in the eyeball, lungs, and abdomen, vibrating the fluid or gas in them, causing fatigue and involuntary muscle contractions.
Lacy picks up the now-empty bottle and blows across the opening. Blowing across the edge of the bottle creates a range of frequencies. She could play a song with a row of bottles filled by varying amounts. The cavity inside enhances the resonant frequency of the bottle (determined by the size and shape of the bottle). Flutes, recorders, and organ pipes change notes by changes in cavity size and shape.
CLAY
That’s like a referee’s whistle.
It is. Air blown in creates a tone by vibrating an edge. The cavity shape sets the frequency. A ball bouncing inside makes the whistle warble by briefly blocking air holes.
Alan tapped the nail of an index finger against the side of the empty bottle. It made a predictable tink, tink sound. Now listen to this, he said, placing the bottle on one of the empty garage sale tables. Go to the other end of the table and put your ear to the table to listen. Clay complied. Alan again tinked the side of the glass bottle. It was much louder compared to the tink sound in open air.
In open air, sound spreads out in all directions and quickly converts to heat when absorbed. Through the wooden table, the sound does not spread out. It is confined to a smaller volume and is more directed. The sound is directed through the table like a megaphone. Or like train tracks. Sound travels faster through metal than through open air. That’s why listening for a train with an ear to the rail works.
LACY
Sound travels faster through water too. Once I was in the pool, rising up out of the water as Clay lit a firecracker. I heard it underwater, then again in the air a fraction of a second later.
frequency varies with motion
Radar Guns, Bat Meals, and Echograms
The engine sounds louder and the pitch becomes higher as Karl’s motorcycle approaches. Higher because sound waves enter your ear more often. The same thing happens noticeably with a fire truck siren. As Karl zooms past, waves enter your ear less frequently and the pitch drops. Higher pitch on approach; lower pitch moving away.
Police can use this fact to measure the speed of oncoming vehicles. Police use a radar gun. Radar waves reflect off moving cars. If there is an increase in how frequently the waves that bounce back, then the vehicle is over the speed limit set by the police radar gun.
Bats also use this technique. They send out a chirp. A moving moth toward the bat, like Karl’s motorcycle approaching, returns a frequency higher than the chirp. Lower frequency, if retreating.
To defend against bats, some moth species have evolved fuzzy bodies. The fuzz works like a muffler or ceiling tile; it absorbs sound—in this case, the bat’s chirp—and so seems invisible to the predator bat.
If a bat and the moth were moving the same direction at the same speed, then the bat would detect no frequency change and the speedy moth would seem invisible. Same if the police are chasing a speedster.
If a large stationary ball was spinning fast, a police radar gun would detect one side moving toward it and the other half of the spinning sphere moving away. Yet the ball is stationary.
Astronomers use a technique similar to the radar gun on a spinning ball. They can tell which direction a distant star is spinning and whether the star is approaching or moving further away from us.
Lark, Karl’s wife, works in the echo department of the local hospital. She uses a similar technique to harmlessly see a baby that is still in the womb using ultrasonic waves; sound higher than we can hear.
Ultrasound vibrates more than 20 000 times each second. When these waves bounce off the outside a hand or face, an image appears on a monitor. Lark can see the outline of the baby and its beating heart.
ALAN
Returning to Karl’s motorcycle, the pitch changes if it is idling and I approach fast on my bicycle.
It doesn’t matter who is moving closer. As long as one is approaching, the perceived pitch will be higher. That’s how bats detect cave walls and stalactites.
radio waves are vibrating electrons
Radio Tunes, Ghost Images, and Male Foghorns
Alan has a transistor radio for the garage sale. Even the small ones are bulky compared to modern electronics. Sound needs vibration of matter, such as air or water. In deep space there is no matter, so no vibration. A rocket would be silent, as would a star exploding or the Big Bang itself. The Big Bang had no bang.
That said, radio waves transmit nicely in outer space. They are a different kind of wave, more like magnetism than vibration.
ALAN
Radio waves are all around us, passing right through us.
CLAY
Broadcasts from country and classical stations are passing right through me as we speak?
ALAN
Yup, that and news talk, pop, and hard rock. All moving almost the speed of light.
To make the transistor radio play 101 FM, Alan turns a dial. The dial adjust the natural frequency of electronics inside the radio. When they match a broadcast signals, the station is tuned-in.
Station 101 FM sends out radio waves at a certain frequency. The electrons in the antenna of the station’s transmitting tower vibrate that frequently. FM 101 means 101 million vibrations each second.
By turning the dial, Alan tunes the radio set so that the radio electronics resonate to that station. He hears music because magnets in the radio pull on paper speaker cones to match the signal.
Speakers vibrate when pulled and let go by the magnet. Vibration of the speaker cones vibrates the air and that is what we hear. Bigger and better speakers would produce better music, of course.
In an automobile equipped with AM and FM radio, the AM reception cuts out under a bridge, yet FM reception continues. AM wavelengths about the length of three soccer fields. Large objects absorb long waves.
FM waves are about the length of a ping pong table. Signals in this range are not absorbed by large objects such as buildings or bridges. Instead, they are reflected and scattered in all directions.
FM signals can become distorted. If a direct and a reflected signal from the same station are received at nearly the same moment, they cause ghost images on television and distortion or noise on FM radio.
Sound waves are absorbed as heat. Not a lot of heat, but some. Heat eventually makes its way into outer space. Higher frequencies have more energy and convert to heat faster than lower frequencies and so travel less far.
Foghorns use low frequencies, to reach further out to sea to warn ships. It is also why we tend to hear lower male voices in a crowd over the higher energy female voices at the same volume.
colour varies with light frequency
Bright White, Blue Sky, and Fast Food Red
Mona and Lark are putting out a few paintings at the garage sale. One shows a mountain with a bluish tinge. The artist used blue to bring out the white of snow and suggest cold.
MONA
That reminds me, I want to put fabric whitener in the wash now that the kids are playing sports. A bit of bluing for their jerseys.
Blue reflects more light, making clothing appear whiter than white.
LARK
I used it on my wedding dress. My mother’s dress, actually. It’s an heirloom. The yellow of age disappeared. I added a little to the swimming pool and the pool has a sparkling clean gleam.
The colour seen is the hue reflected. For the dress to look yellow, the cloth absorbs all hues except yellow. The yellow is reflected back to our eyes. A black dress absorbs all hues. A white dress reflects all hues.
White is all colours combined, such as light from the sun. When white light enters a prism and exits split into all hues of the visible rainbow, red to violet. Black is the absence of colour, such as a shadow.
Fresh water and window glass are not invisible. You can see them, at least by shine and shimmer. They are colourless because they let light of all visible frequencies pass through equally.
In order to be visible, emergency vehicles are painted yellow-green. Our eyes are most sensitive to yellow-green. And the sky is blue because blue is reflected when sunlight scatters off nitrogen and oxygen in the air.
MONA
I am not sure whether to brighten the colours of Clay’s paint-ball outfit. Grunge might be an advantage. But if I don’t wash them, they will have a smell-camouflage and stink.
Despite the name, there is no paint in a paintball. It contains a water-soluble dye so the colorant washes out.
A paintball is used as part of a sports arsenal, but the makeup of a paintball is more like a laxative. Most of what is inside a paintball is a chemical sometimes used to treat constipation. It causes water to be retained with the stool, but even the coating is essentially a gel capsule.
Food colours with which we are familiar are not necessarily natural. There is colouring in a hot dog, or it would be grey. Artificial colour is even added to orange juice to make it brighter orange.
Colour has associations. We associate green with the environment, but also with being raw, unripe. Green bananas, for instance. That association may be why green is seldom on milk cartons. Red and yellow makes us want to eat, so they are favourite colours in the design of fast food restaurants. On the other hand, blue and pink tend to be less appetizing. There are few blue restaurants.
colour reflected is colour detected
Prisms, Pigments, and Rusty Apples
Under the summer sun of their yard sale, Lark sets out an assortment of mismatched crystal wine glasses. Sunlight striking each goblet stem casts a red, green, blue spectrum against a box on the table. Lark turns the goblets so that red from one goblet overlaps with green from another. The result is yellow.
Lacy took crayons out of the box and drew a red patch on top a green patch. The result was brown. Adding more crayon colours eventually made black. Color from the goblets comes from the white light of the sun. Color from the crayons comes from pigments added to the wax stick of the crayon.
Comic books are printed with pigment ink in layers, building up a four colour image. Part of a scene is first printed in dots of magenta ink, then part with dots of yellow ink, then cyan ink and a bit of black.
Ink is typically used for surface application, such as printing, and contains insoluble pigments. Dye is usually soluble and used to colour materials thoroughly so that colour becomes a part of the object. For instance, a postcard is written in ink; a basket is dyed blue.
Whether ink or dye, the spectrum of light that is reflected is the apparent colour observed. If yellow is reflected, then the object appears yellow. It absorbs all hues of the visible spectrum except yellow.
Comic books, like newspapers and paperback novels, turn yellow with age, especially if left out in the sun. Comics, newspapers, and paperbacks considered disposable are printed on cheap paper.
Paper is made from cellulose, which is mostly tree pulp. Cellulose absorbs light and oxidizes (combines with oxygen). Oxidized cellulose reflects a yellow hue. The process is similar to how iron rusts.
An apple turns brown where a bite is taken. A bicycle chain rusts. Copper forms a green patina. Silver tarnishes to a dull grey. All are instances of matter mixing with oxygen and all are related to fire.
Yellowing comics, tarnishing silver, and rusting chains are slow compared to fire, but they are all related to the same process. Fire is rapid oxidation: oxygen from the air plus, say, wood at a campfire.
Rapid oxidation is why incandescent light bulbs do not contain air. Instead of air, argon gas is used inside an incandescent bulb. Oxygen in air would quickly oxidize the filament and the bulb burn out.
Nuts and seeds have a lot of oil. So do potato chips. When the oil in food oxidizes, the food has become rancid. To slow oxidation, keep food in a sealed container, stored in a cool or cold, dark place.
To keep a bag of chips from turning rancid, they are vacuum-packed in nitrogen at the factory. Air is vacuumed out and nitrogen pumped in. Nitrogen does not react; no oxidation, no rancid potato chips.
Lacy uses rancid oil, provided it does not contain salt, to lubricate her bicycle chain and keep it from rusting.
LACY
Using rancid oil to prevent rust is a slow-motion case of fighting fire with fire.
light and sound are forms of energy
Tan Ban, City Heat, and Twinkle Little Stars
On the road a lot, Karl drives his truck with the driver’s window down, weather permitting. Arm on the window sill, he has developed a nice tan around his left elbow. The rest of Karl shows no tan.
Automobile glass, and glass in general, does not let in the kind of light that promotes tanning: ultraviolet light. Only Karl’s elbow, outside the window, is exposed and so only his elbow is tanned.
Karl starts out the day with windows up, letting the morning sun warm the seats and dashboard. It is a small example of the greenhouse effect. Heat is trapped in the truck’s interior.
Something similar happens in Earth’s atmosphere. Water vapour, carbon dioxide, and methane gas act like the truck’s compartment and trap heat. Trapped heat raises the temperature all over the globe.
The sun produces ultraviolet light, which has more energy than visible light. This extra energy can be harmful to the nucleus of a skin cell, so the body protects itself by increasing the amount of melanin in the cell.
Melanin is a dark pigment that forms a layer over the cell to filter out ultraviolet. A melanin layer is like a window shade or sunglasses. It filters light, resisting harmful rays that might damage skin cells.
Glass absorbs ultraviolet light. The thicker the glass, the more the absorption and less chance of sunburn. Clouds are transparent to ultraviolet light and so offer no protection against sunburn.
As the truck warms up, Karl tunes in his favourite radio station, FM 101. The cabin fills with light and sound. Both are forms of energy and they are absorbed by material in the truck cabin, including Karl. They are absorbed, not trapped. Trapped sound would still be in the truck’s cab and could be heard if one gets close. Light and sound convert to heat when absorbed and this heat is then radiated into the atmosphere.
The radio station and ultraviolet light are on the same spectrum as wavelengths visible to Karl. Even so, Karl can see only those in a narrow band, from red to violet—the visible colour spectrum.
Most of the sunlight that reaches the Earth falls in that red to violet range. The human eye is most sensitive to light in the yellow-green range, which coincides with the peak of our sun’s energy output.
The shorter the wave, the more energy it carries. Wavelengths shorter than those of visible light, such as X-rays and ultraviolet radiation, carry enough energy to destroy organic molecules in the eye.
Longer wavelengths, such as infrared radiation and microwaves, do not have enough energy to trigger changes in molecules of the retina. As a result, no visual impulses will reach the brain. No image.
Driving through the city, Karl lowers the air conditioner. City temperature is about five degrees higher than the countryside. There is less wind in a city due to taller and more complicated structures.
The city is warmer partly due to less expansive evaporation, as on a grassy field. Evaporation cools by losing latent heat going from liquid to gas. Paving and building materials also store more heat than soil does.
Karl’s work often takes him to the airport. Airports are notoriously noisy. Not this one, or at least not as noisy as most. Karl’s airport is on a plateau higher than the city. It is an elevated airport.
An elevated airport is quieter to the city in the valley below. Sound waves from the airport tend to go upward into the sky, rather than down into the valley. The cause is wind and temperature differences.
The human eye has tiny rods and cones. Rods are triggered in faint light, such as Karl driving at night. To see a faint star he looks to the side of it so the image falls on a part of his eye where rods pick it up.
We see moonlit objects mainly with rods in our eyes. Objects in moonlight appear black and white, even if they have colour by day. Light reflected by moonlight is too dim to trigger the cones, and it is cones in the eye that perceive colour.
KARL
Cruising the countryside at night, I can watch the stars twinkle.
Actually, he cannot. They don’t twinkle. Uneven heating in the air makes air turbulent. The wavy air makes stars appear to twinkle.
Parcels of turbulent air bend starlight one way then another. The shimmering air can be seen above heated surfaces, such as a match or stove. Over hot pavement, it might look light water on the road.
light and sound can be absorbed or reflected
Kitchen Prep, Knuckle Noise, and Sooty Snow
The garage sale was a success and Karl and Lark invited a few neighbours over for a barbecue. Preparation starts in the kitchen, which, unlike the family room, is bright and noisy. The kitchen is painted white, like the exterior of the house, to keep it cooler. The kitchen is also noisy. It has marble counter tops and tile floors and sound bounces off hard surfaces such as these.
Another way to maintain house temperature is with double pane windows. Double pane has a thin layer of gas between two panes of glass. The gas is an insulator; it resists letting heat pass through.
Triple-pane windows are not much better than double since even a thin layer of gas-filled space is enough. The thickness of the gas-filled space is not significant. Triple pane is about equal to double pane.
Colour affects how much light is reflected, which affects temperature. Karl is cooler with a white shirt rather than a black shirt since white reflects better. Sunlight causes fading, so a white shirt also lasts longer.
In the kitchen, paper towel is used to absorb spilled milk. Paper fibres have small spaces to take in the liquid. Absorption of sound also needs small pockets. Hard surfaces will reflect sound back in a room.
Aluminum foil is smooth, at least on one side. It is dull on the other side. That is a result of how aluminum is made. Both sides are the same metal and so, for baking, it does not matter which side is in or out.
The family room has carpet, drapes, a fabric couch and acoustic ceiling tiles, all of which trap light and sound. Acoustic tiles act like an automobile muffler: sound fills small chambers, called baffles.
Spilled milk can be absorbed with paper towel. Gases can also be absorbed, sometimes even into liquids such as the fizz in a can of soda pop. Carbon dioxide absorbed in pop gives it fizz.
Knuckle cracking is like pop can fizz. There is fluid between finger joints, synovial fluid, that absorbs carbon dioxide. Pulling or pressing makes knuckles “crack” by separating bones, lowering pressure.
Lowering pressure releases the absorbed carbon dioxide as bubbles. As bubbles collapse, they produce a pop sound. After a while, the gas reabsorbs into synovial fluid and knuckles are ready to crack again.
Light rays can also be absorbed. Garden dirt absorbs most of the light that hits it, making it a poor mirror. Albedo is the percentage of energy reflected from an object. The albedo garden soil is about 10%.
To say the albedo of soil is about 10% means dirt reflects 10% and takes in 90%. Higher albedo means higher reflection. Fresh-fallen snow is about the opposite of soil. It reflects about 90%.
To prevent floods, airplanes drop soot on snowy mountain sides before spring. Soot has a low albedo; it absorbs energy from the sun and so helps the snow melt slowly to prevent rapid-melt run-offs.
Light on an object will be absorbed (taken in), transmitted (passed through), or reflected (bounced back). The charcoal briquettes in the BBQ absorb light. They are opaque. You can’t see through them.
A glass pitcher of water is transparent: you can see right through it. Waxed paper, under the burger patties, is translucent. It lets diffuse or scattered light pass through, like a frosted-glass shower door.
