Vibrations and Waves
Vibrations and Waves
Vibrations and Waves
Chapter 11
Simple Harmonic Motion
Chapter 11 Section 1
Periodic Motion
Any repetitive, or cyclical, types of
motion
– Examples?
Chapter 11 Section 2
Amplitude
The maximum displacement
from equilibrium.
Period
The time it takes for one complete cycle of
motion.
Represented by the symbol T
Unit of seconds
Frequency
The number of cycles completed in a unit
of time (usually seconds)
Represented by the symbol f
Unit of s-1 (also known as Hertz)
Period and Frequency
Period and frequency are inversely
related.
Crest
Trough
Longitudinal Waves
Particles of the medium move parallel to the
direction of energy transfer (slinky demo)
Be able to Identify compressions, rarefactions,
wavelengths
Compressions Rarefactions
Waves transfer energy
Note that, while energy is transferred from point A
to point B, the particles in the medium do not move
from A to B.
– Individual particles of the medium merely vibrate
back and forth in simple harmonic motion
A: 0.0300 m
Practice #2
Q: The piano string tuned to middle C
vibrates with a frequency of 264 Hz.
Assuming the speed of sound in air is 343
m/s, find the wavelength of the sound
waves produced by the string.
A: 1.30 m
11.3 Problems
Page 387 1-4
Page 388 1-5
Wave Interactions
Chapter 11 Section 4
Interference
The combination of two or more waves in a medium at the same time.
– Matter cannot occupy the same space at the same time, but energy can.
The Superposition Principle describes what happens when waves
interfere…
– Waves (energy) pass through each other completely unaffected
– The medium will be displaced an amount equal to the vector sum of what the
waves would have done individually
Constructive Interference
Waves are on the same
side of equilibrium.
Waves meet, combine
according to the
superposition principle,
and pass through
unchanged.
Amplitude larger than
originals
Destructive Interference
Waves are on the
opposite sides of
equilibrium.
Waves meet, combine
according to the
superposition principle,
and pass through
unchanged.
Amplitude smaller than
at least one original
wave
Complete Destructive Interference
Interference patterns
Interference
patterns result
from continuous
interference.
Check it out!
Reflection
The bouncing of a wave when it
encounters the boundary between two
different media
Fixed End Reflection
At a fixed boundary, waves are inverted as they
are reflected.
Free End Reflection
At a free boundary, waves are reflected on the
same side of equilibrium
Standing Waves
A wave pattern that results when two waves of
the same frequency, wavelength, and amplitude
travel in opposite directions and interfere.
Standing wave parts
Node – point that maintains zero displacement
Antinode – point at which largest displacement
occurs
Standing waves
Only certain frequencies produce standing
wave patterns.
If a string is 4.0 m long, what are
three wavelengths that will produce
standing waves on this string?