Sound
Note: please read the waves page before you read this!!!!
What is sound?
Sound is a longitudinal wave. It needs a medium to travel - a solid, liquid, or gas. It cannot travel through a vacuum. Sound occurs when a material vibrates.
It is the compressions and rarefactions of its longitudinal wave. For example, in a saxophone (or any musical instrument), the vibrations coming out of it makes the air around it vibrate - which is the reason we can hear it at all.
Our interpretation of a sound's frequency is its pitch. A flute has a high pitch while a tuba has a low pitch (I'm a band kid ok leave me alone).
The human frequency range goes from 20 Hz to 20000 Hz, and it shrinks as we age because we suck. Sound waves lower than 20 Hz are infrasonic while sounds higher than 20000 Hz are ultrasonic. I'm so sorry but all I can think of is that crunchy blue hedgehog 😭
Air actually sucks as a conductor of sound when compared to solids and liquids - its molecules are farther apart. Sound is slower than light - hence why you see lightning before hearing thunder and why you sometimes see a car door close before you hear it when you're far away.
In dry air, the speed of sound is about 330 m/s. With water vapor, this speed increases slightly. Sound travels faster in warm air than cold air, because warm air particles hit each other more often than cold air particles do. However, in water, the speed of sound is about 4 times its speed. In steel, it is about 15 times faster.
Reflection, Absorption, and Refraction
Reflection is what happens when sound waves bounce off an object. Absorption happens when sound waves are absorbed by an object. A sound reflection is called an echo. When sound reflection happens over multiple surfaces, it is a reverberation. If you think this is cool, you should go into acoustics - the study of sound properties.
Refraction is happens when sound waves bend. It happens when sound waves are affected by uneven winds or uneven temperatures. since sound travels faster in warm air, it bends away from the warm air.
Forced Vibrations and Natural Frequencies
When an object is forced into vibration by another object, it is called forced vibration. The example in the physics textbook (cited on the welcome page) is quite good, so here it is: if you hit a tuning fork in the air, it sounds faint. but if you hit a tuning fork against a table, the sound is a lot louder, because the table is forced to vibrate with the fork.
Every object has a natural frequency - they vibrate at their own frequencies, which are determined by a multitude of factors like its shape and elasticity. Resonance is when forced vibrations on an object match its natural frequency, increasing the amplitude of its waves.
The Doppler Effect and Bow Waves
One crazy thing about sound is the Doppler effect. If an object is moving and producing sound waves, like a fighter plane, the waves in the front are closer together than they are in the back, so the frequency gets higher as the object moves closer and lower as it moves farther away.
If the fighter plane is moving at its wave speed, a wave barrier produced, forming a lump in front of the fighter plane. It is in the shape of a V, called a bow wave. But if the plane passes that lump, a sonic boom is heard and the plane is now supersonic. The sonic boom actually travels with the object that travels faster than sound.
Well, I'm hoping you enjoyed this page. Please do check out the light page! See you in the next one!