Sound
There are two general types of waves, TRANSVERSE and LONGITUDINAL. The motion of vibrating and oscillating source is called simple harmonic motion.
Transverse wave is the wave that the direction of travel of the wave is perpendicular to the motion of the source. Longitudinal wave is the wave that the travel of the wave is parallel to the motion of the source
Example: water waves area combination of the action of both kinds of waves, transverse and longitudinal. The particles of water move in circular path, sometimes they are parallel to the direction of wave motion, and at other times they are perpendicular to the direction of wave motion.
Terms in periodic waves: Cycle is a complete sequence of motion that repeats itself
The wavelength (λ) is the length in meters of one cycle.
The period (T) is the time to complete one cycle in seconds.
The frequency is the number of cycles in a given time period.
Hertz (Hz) is s-1
The amplitude of a wave is a maximum disturbance of a wave from its zero point in meters.
Wave equation: v= and T= v= λf
Sound is a longitudinal wave that requires a medium to travel in. Air cannot sustain a transverse motion because air particle drift off.
The dense areas of air transmitting a sound wave are called compressions and the less dense areas are called rarefactions.
The folds of skin vibrate as the air rushes by them, producing sound in the form of compression and rarefaction of air. These waves are amplified and modified by the group of parts collectively called the resonators. They are the pharynx, mouth, and nasal cavity.
Factors that are affecting the speed of sound are temperature and density.
The stiffer the material, the faster the speed of sound. Molecules of a solid behave as if they were held together by springs. They proximity allows the vibrations caused by sound energy to be easily transmitted. Gas molecules are separated by great distances. Hence, transmission of energy is less efficient.
Dependence of speed on temperature: v=332m/s+(0.6 )(T x°c)
When aircraft gets close to or go faster than the speed of sound, a different unit is often used to describe their speed. It is called the Mach number.
If you are travelling at greater than Mach 1, your speed is said to be supersonic. If you are below Mach 1, your speed is subsonic. Speeds greater than or equal to Mach 5 are hypersonic.
Sound barrier is used in aviation to describe the buildup of sound waves in front of a plane as it nears the speed of sound.
Sonic Boom: as a plane flies over a region, the pressure cone follow, creating sonic booms for that area.
At Mach 1, a barrier of pressure builds up. As the plane breaks through it, the shock wave is left behind, which travels down to the surface of Earth. We hear it as a loud “boom”.
