When we think of waves, we think of a sea beach with waves hitting the shore or a water pond with ripples running out in various directions.

But, the fact is that we are living in the middle of a plethora of waves. Whatever we hear and whatever we see is possible only due to some form of wave motion. As a matter of fact, the waves do not stop with visible light and audible sound. What scientists found out is that the total spectrum of light goes into a larger, invisible range of electromagnetic (infrared and ultraviolet, microwave and x-ray waves) and sound extends to ultrasonic range that are not audible to humans. Interestingly some animals like dogs can hear such sounds!!

Let’s try to get into this strange world of light and sound –

What is light made of?

This is not an easy question. Light has no mass and is not really considered matter. So does it even exist? Of course it does! We couldn’t live without light. Today scientists say light is a form of energy made of photons. Light is unique in that it behaves like both a particle and a wave.

Why does light go through some things and not others?

Depending on the type of matter it comes into contact with, light will behave differently. Sometimes light will pass directly through the matter, like with air or water. This type of matter is called transparent. Other objects completely reflect light, like an animal or a book. These objects are called opaque. A third type of object does some of both and tends to scatter the light. These objects are called translucent objects.

Light helps us to survive

Without sunlight our world would be a dead dark place. Sunlight does more than just help us see (which is pretty great, too). Sunlight keeps the Earth warm, so it’s not just a frozen ball in outer space. It also is a major component in photosynthesis which is how most of the plant life on Earth grows and gets nutrients. Sunlight is a source of energy as well as a source of vitamin D for humans.

The speed of light

Light moves at the fastest known speed in the universe. Nothing moves faster than (or even close to) the speed of light. In a vacuum, where there is nothing to slow it down, light travels 186,282 miles per second! Wow, that’s fast! When light travels through matter, like air or water, it slows down some, but it’s still pretty fast.

To give you an idea as to how fast light is, we’ll give you some examples. The Sun is almost 93 million miles from the Earth. It takes around 8 minutes for light to get from the Sun to the Earth. It takes around 1.3 seconds for light to go from the moon to the Earth.

Refraction

Normally, light travels in a straight path called a ray, however, when passing through transparent materials, like water or glass, light bends or turns. This is because different materials or mediums have different qualities and different densities.. In each type of medium, whether it is air or water or glass, the wavelength of the light will change, but not the frequency. As a result, the direction and speed of the traveling light wave will change and the light will appear to bend or change directions.

One example of refraction is a prism. Prisms are unique in that each color of light is refracted to a different angle. So it can take white light from the Sun and send out light of various colors.

Lenses use refraction to help us see things. Telescopes help us to see things far away and microscopes enable us to see very small things. Even glasses use refraction so that we can see everyday things more clearly.

Sound

Sound is a vibration, or wave, that travels through matter (solid, liquid, or gas) and can be heard.

How does sound move or propagate?

The vibration is started by some mechanical movement, such as someone plucking a guitar string or knocking on a door. This causes a vibration on the molecules next to the mechanical event (i.e. where your hand hit the door when knocking). When these molecules vibrate, they in turn cause the molecules around them to vibrate. The vibration will spread from molecule to molecule causing the sound to travel.

Sound must travel through matter because it needs the vibration of molecules to propagate. Because outer space is a vacuum with no matter, it’s very quiet. The matter that transports the sound is called the medium.

Speed of Sound

The speed of sound is how fast the wave or vibrations pass through the medium or matter. The type of matter has a large impact on the speed at which the sound will travel. For example, sound travels faster in water than air. Sound travels even faster in steel.

In dry air, sound travels at 343 meters per second (768 mph). At this rate sound will travel one mile in around five seconds. Sound travels 4 times faster in water (1,482 meters per second) and around 13 times faster through steel (4,512 meters per second).

What is the Sound Barrier?

When airplanes go faster than the speed of sound (also called Mach 1), it’s called breaking the sound barrier. Most airplanes don’t go this fast, but some fighter jets do. When they pass through the speed of sound, the airplane sheds water drops that have condensed on the plane creating a cool looking white halo (see the picture above).

When planes break the sound barrier they also create something called a sonic boom. This is a loud noise like an explosion that is generated from a number of sound waves that are forced together as the plane is now traveling faster than sound.

Volume

The volume of sound is the measure of loudness. To quantify volume we use decibels. The more decibels, the louder the sound is. A soft sound, like a whisper will measure around 15-20 decibels. A loud sound like a jet engine is more like 150 decibels. The threshold of pain occurs at around 130 decibels.

Loud sound can actually damage your ears and cause loss of hearing. Even sounds as loud as 85 decibels can ruin your ears if you listen to them over a long period of time. For this reason, it’s a good idea to not listen to loud music or have your headphones turned up too loud.

Did you know?

Here are some interesting facts about sound and light –

• To measure the depth of sea, we use sound wave technology. Sonar (originally an acronym for sound navigation ranging) is a technique that uses sound propagation (usually underwater) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.

• Nothing can travel faster than light. As per Einstein, if an object with finite rest mass will start approaching the speed of light, it would become infinitely heavy which is not possible.

• If we say that an object is 5 light minutes away, we actually see its image which was 5 minutes ago. Therefore, the stars (which are very far away from our planet) we see at our skies are actually their images of hundreds and even millions of years ago.