Think of water. when you throw a rock, circles that get bigger appear around where the rock falls. That’s because the particles of water vibrates. Energy is spreading in the medium(water).
There are two kinds of waves:
- Mechanic waves: can only spread in physical mediums. Like water, sound, earthquake and spring waves.
- Electromagnetic waves: don’t need a physical medium to spread. they can spread in space. Radio and microwave, X rays and light are electromagnetic waves.
Again there are two kinds of waves according to their vibration direction:
- Longitudinal waves: SPRINGY The vibration direction of particles and direction of wave are parallel to each other. The push you give travels through the spring by compressing it. Sound, earthquake and spring waves are longitudinal.
- Transverse waves: WAVY. The vibration direction of particles and direction of wave are perpendicular to each other. The upward push you give travels up and down. This is because when you lift your hand up, you give energy to the spring. And all the particles of the spring do the same movement by pulling other particles up and down. Spring, earthquake and electromagnetic waves are transverse.
This is the graph of a transverse wave.
- Top of the waves are called crest and the bottom is trough.
- A wavelength is from one crest to the next or from one trough to the next. It’s symbol is shown in the graph. SI unit is meter(m)
- Amplitude is the size of the wave but it is measured from the undisturbed position(equilibrium position) to the crest.
- Period is the time between crests. Symbol is T. SI unit is second(s).
- Frequency shows how many waves pass a point every second. Symbol is f. SI unit is second^-1 or Hertz.
T.f=1 ➜ frequency and period is dependent on the source of wave.
Since the wavelength is from one crest to the other and shows the distance the wave travels and period is again from one crest to the other and shows the time, they will give us velocity when divided. SOUND WAVES:
They are longitudinal and mechanic waves. Which means that they need a material medium like solids, liquids or gases in order to travel. They can’t travel in space.
They are created when a source vibrates back and forth. The sound sources have two types:
- Natural sound sources: human cords, wind, lightning
- Artificial sound sources: musical instruments, cars
When the cone of the speaker moves forward(vibrates), it creates pressure among air molecules. This high-pressure region is called compression. And when cone moves back, the pressure decreases creating a low-pressure region called rarefaction. By this way the energy in the cone is transferred to waves. (Sound is an energy type and it can be transferred into another type.) These vibrating air particles create a longitudinal wave. But this situation can be graphed by transverse wave. Compression regions are the crust(top of the wave) and rarefactions are trough.Frequency of sound:
Every living thing can hear different frequencies of sounds. An average person can detect sound waves between 20Hz and 20,000Hz frequencies. Dogs can hear higher frequencies and elephants can hear lower frequencies.
Low frequencies are considered as low-pitched(infrasound) and high frequencies are high-pitched(ultrasound) sound.
When a sound wave hits a surface and changes its direction, it’s called sound reflection or echo. If a room with lots of furniture has less echo than the unfurnished one. In sonar devices, things like fishes can be detected by ultrasound reflection. The reason of ultrasound being used is shorter wavelengths are necessary to image smaller details. Humans use artificial sound devices where as dolphins and bats have natural ones. They use sound waves instead of sight, to detect their bates and surroundings.
Every object has its own frequency derived from its mass and flexibility. They all vibrate at their own frequency level except one condition.
Think of two diapasons(tuning forks) standing side by side but not touching to each other. If we hit the left one , it’ll start to vibrate in its own frequency. But the right one will start to vibrate, too. The second own will vibrate in the left one’s frequency. But the right one won’t reach its own maximum amplitude, where the left one will.
Loudness of sound:
It’s the volume of the sound. It is calculated by decimeter. SI unit is decibel(dB). When the amplitude increase, volume increase, too.
There are two factors that affect the loudness:
- The distance to the source: Getting further away from the source causes the loudness to lower. Because the sound travels as enlarging circles, its power in a unit surface decreases.
- The power of the source
LIGHT AND ELECTROMAGNETIC WAVES:
Although we don’t realize it but we use electromagnetic waves a lot in our daily life. Our cellphones, laptops, radios and Wi-Fi are all a result of electromagnetic waves. Surprisingly light is one of them, even though it is the only one we can see with our eyes. All these waves have the same physical characteristics except light’s visibility to our eyes. They can be refracted and reflected,
They are transverse waves that carry energy and can travel in vacuum, space, air. In a medium they travel with same speed: c=3.00 x 10^8m/s. But their speed depends on the medium. If the density of the medium increases, their speed decreases.
They are named according to their wavelength and frequency. Radio waves have the smallest frequency but largest wavelength. In contrary, X rays have the largest frequency and smallest wavelength.
Light has a short wavelength approximately 400nm(=400×10^-9m) TO 700nm(=700×10^-9m). In the electromagnetic spectrum each wavelength has its own color. In visible light section, purple is the shortest and red is the largest wavelength.
Breaks under earth’s layer causes earthquakes. Earthquakes are called seismic waves and they are infrasound. There are two types:
- Body waves: Spread from inner layers of earth
- Primary waves(P-waves): It’s parallel to surface. It’S the first wave to be recorded during an earthquake. It’s speed is between 1.5km/s and 8km/s. It can be sensed by some animals.
- Secondary waves(S-waves): It’s perpendicular to surface. Its speed is half of P-waves. It vibrates up and down, right and left.
- Surface waves: Spread slowly along surface. They are more destructive than body waves.
- Love waves: Moves the earth horizontally. It’s a transverse wave.
- Rayleigh waves: Moves slower than love waves. It draws an ellipse just like ocean waves and it’s the most felt wave.
As we said earlier, when a rock is thrown into a water, circles appear around the contact point. And those circles enlarge while going further away from that contact point. Water waves vibrate up and, left and right while moving. They are both longitudinal and transverse waves.
- When the frequency increases, the length decreases.
- When the depth increases, the wave moves faster.