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.