Wave Motion and Interference Phenomena

Wave Motion

• Wave motion is the transfer of energy through a medium, characterized by periodic disturbance.
• Energy is transferred, but the medium itself doesn't move in the direction of energy transfer.
• Movement occurs perpendicular, between minimum and maximum amplitudes of displacement.

Sinusoidal Wave Motion

• Sinusoidal wave motion follows the pattern of a sine wave.
• Sine waves are graphical representations of angular sine values.
• Compression and longitudinal waves are pulses that create compressions and rarefactions through a medium.
• Sound waves are compression waves, using the mechanical action of molecules for transfer.
• Sound waves cannot travel through a vacuum, unlike light waves, which are not mechanical.

Interference Phenomena (Superposition)

• Wave effects are superimposed algebraically.
• Overlaying identical sine waves of the same frequency results in a wave with double the amplitude.
• Different phase waves can cancel each other out.
• Constructive interference is when waves combine to amplify each other.
• Destructive interference is when waves combine and cancel out each other.
• Interference patterns are evident in the constructive and destructive interference of light, shown on a screen through slits.

Standing Waves

• Standing waves form when a fundamental wave interferes with a harmonic wave, creating a new wave.
• These waves result from waves traveling in opposite directions, converging and thus creating interference patterns.
• Nodes in standing waves have zero amplitude.
• Antinodes have maximum amplitude in these wave patterns.
• Harmonics are multiples of the fundamental wave's frequency.

Resonance Damage

• Objects have natural frequencies.
• A forced vibration, when frequencies match natural frequency, increases amplitude dramatically.
• This can cause damage to mechanical systems.
• Tail booms, blades, and general mechanics must be checked for avoiding resonance issues.

Beats

• Sound waves with close frequencies create beat frequencies by interference.
• The beat frequency is the difference in the frequencies.
• This is a result of the varying amplitude of the interference.
• Twin engine aircraft propellers create noticeable "thrumming" when they run at mismatched RPMs.

Sound Intensity

• Sound intensity is determined by the amplitude of a sound wave.
• High amplitude means louder sound.
• It's measured in decibels (dB).
• Intensity levels of everyday sounds vary greatly.
• Intensity decreases with the square of distance from the source.

Sound Pitch

• Pitch is determined by the frequency of the sound wave.
• Higher frequencies correspond to higher pitch.
• Human hearing range is ~20Hz - 20,000Hz.

Sound Quality ("Timbre")

• Quality or "timbre" is how a sound is characterized.
• Dependent on the nature of harmonics present.
• Harmonics have numerical values determined by multiples of the fundamental frequency.
• Instruments have distinctive sounds due to their unique harmonic relationships.

Speed of Sound

• Speed depends on the medium's elasticity and temperature.
• Speed is greater in denser mediums.
• Normal atmospheric conditions at sea level mean speed ~340 m/s.

Mach Number

• Mach number is used at high speeds.
• A ratio of aircraft speed over local speed of sound.
• Aerodynamic forces are dependent on the Mach number.
• Local speed of sound is about 39√T (T being the temperature in Kelvin)

Doppler Effect

• Doppler effect occurs when a sound source moves relative to a listener.
• Perceived frequency changes as source moves toward or away.
• Sound becomes louder before and then decreases as the source passes by.

Conclusion

• Summary of learned topics and capabilities.
• Recap of key points of wave motion, frequency, and sound.