Pre-AP Physics: Unit 7 Vibrations, Waves, and Sound Part...
Transcript of Pre-AP Physics: Unit 7 Vibrations, Waves, and Sound Part...
Pre-AP Physics: Unit 7Vibrations, Waves, and Sound
Part 2Wave Properties
What is a Wave?
– A disturbance that carries energy and momentum as it propagates through matter or space.
What is a Wave?
The Two Major Categories of Waves• Mechanical Waves
– Require a physical medium to travel through.
o Examples– Sound waves
– Water waves
– Spring waves
The Two Major Categories of Waves
• Electromagnetic Waves– Do not require a physical medium.
o Example: – light can travel through empty space
Types of Waves
• Transverse Waves– Particles move perpendicular to the wave.
Types of Waves
• Longitudinal Waves– Particles move parallel to the wave.
Types of Waves
• All electromagnetic waves are transverse and mechanical waves can be transverse or longitudinal.
Wave Description• Transverse Waves
o Crest
o Trough
o Amplitude– Maximum displacement from equilibrium position.
– How much energy the wave is carrying.
o Wavelength– The distance from one point on a wave to the same point on the next
wave.
Wave Description• Longitudinal Waves
o Compression– Region of higher
concentration.
o Rarefaction– Region of lower concentration.
o Intensity– How much energy the wave is carrying.
o Wavelength– The distance from one compression/rarefaction to the next.
Wave Description• Frequency and Period of Waves
– Same as with simple harmonic motion.
– Frequency• Number of waves that pass by
each second.
• Measured in Hertz.
– Period• The time needed for each wave
to pass by.
• Measured in seconds.
Wave Description• Wave Pulses vs. Periodic Waves
o Wave Pulse– a single, independent
wave.
o Periodic Wave– produced by a continuously oscillating source.
Properties of Waves• Wave Motion
– Waves transfer energy!
– Matter has little or no net movement.
Properties of Waves
• Wave Speedo Equation
v : wave velocity (in m/s)f : frequency (in Hertz)λ : wavelength (in meters)
λ = “Lambda”
Example 3A person standing in a canyon plays a note from a trumpet with a frequency of 110 Hz. The speed of sound at that spot is 330 m/s.a. What is the wavelength of the sound wave?– Answer: 3 meters
b. The sound wave reflects off of a canyon wall and the person hears the echo 4 seconds later. How far away is the person from the wall?– Answer: 660 meters
Properties of Waves
• Reflection– When a wave encounters a boundary and “bounces” off.
Properties of Waves
• Reflectiono Reflection from a free end
– The wave returns on the same side (in phase).
Properties of Waves
• Reflectiono Reflection from a fixed end
– The wave returns on the opposite side (out of phase).
Properties of Waves
• Refraction– The bending of a wave as it enters a new medium.
– This happens because the wave changes speed.
Properties of Waves
• Diffraction– The bending of a wave around the edge of a boundary or
obstacle.