2.5 Wave Motion and Sound Flashcards
What is a mechanical wave?
An oscillation of matter, that requires a medium through which to transmit energy.
What are some examples of mechanical waves?
Sound, slinkys and water.
What distinguishes a mechanical wave from an electro magnetic wave?
Mechanical waves cannot exist in a vacuum.
How can mechanical waves be classified?
Transverse or longitudinal.
What is a transverse wave?
Causes the medium to vibrate perpendicular to the direction of travel. The highest point is the crest and the lowest is the trough.
How are water waves transverse?
The molecules move up and down in the water whilst the waves move left to right.
What is a longitudinal wave?
The displacement is parallel to the movement of the wave.
What are the two types of movement in a longitudinal wave?
When they are close together it is compression and when they are spread out it is rarefaction.
What is a sine wave?
A waveform that repeats itself in fixed form.
What is amplitude?
The highest point of displacement from the rest point. (How high the peak goes from the centre line).
What is wavelength?
The space between each peak.
What is periodic time?
The time taken to complete one oscillation.
What is the frequency?
The number of oscillations in one second.
What is the formula for wavelength?
Wave speed (v) divided by frequency (f)
What is wave interference?
When two waves meet on the same medium and form a resultant wave that can be greater, lower or the same amplitude.
What is a standing wave?
Where two waves meet and the oscillation causes a mixed result. Sometimes the oscillation will be maximised and other times it will be net zero.
What is the speed of sound ?
Air-343m/s
Water- 1500m/s
Steel- 5000m/s
Why is the speed of sound in air important?
For aerodynamics, it is the point at which the air is increasingly compressible and flying characteristics change dramatically.
What does the speed of sound depend on?
The ambient temperature.
What is the equation for the speed of sound?
20 x √T
What is the mach number?
The speed of the aircraft in relation to the speed of sound.
What is propagation of sound?
Production of sound through an elastic medium such as air.
How is the intensity or amplitude of a sound specified?
Pressure- decibels or SPL (sound pressure level)
What decibel level if exposed too for a prolonged time can cause damage?
85db
What is maximum level an human ear can withstand?
130db
What is the doppler effect?
The change in frequency of a wave caused by the movement of a body relative to the wave source.
What is a good example of doppler effect?
An ambulance driving past with the sirens on.
Where is the doppler effect used in aircraft?
Weather radars to detect turbulent weather by measuring the motion of rain droplets in addition to the intensity of precipitation.
