C-25 Warm-Up Question: What do pendulums,
springs and waves have in common?
They all exhibit
periodic or simple
harmonic motion!
4&8
A swinging pendulum or bouncing
spring creates a wave or sine curve.
Pendulum Motion
The back and forth motion
(vibrations or oscillations) of
a swinging pendulum is
called simple harmonic
motion.
Š The restoring force is
proportional to the
displacement from
equilibrium.
2
Pendulum Motion
The period (number of seconds
for one complete swing) of a
pendulum depends only on the
length of the pendulum and the
acceleration of gravity.
Examples of Waves and
Vibrations:
Š Swings of a pendulum, trees in the wind
Š Waves in a lake
Š Electrons vibrating in an antenna
Š Sounds from voices, music, nature
Š Light, x-rays and other energy (EM waves)
Š (The material that a wave travels through does
not travel along with the wave, like a rope.)
Frequency is the
number of cycles
per second.
9
Parts of a Wave
1
1-crest
2-trough
3-wavelength(lambda-λ)
4-amplitude
---equilibrium
Node
Antinode
4
3
2
Frequency is measured in Hertz (Hz)
Frequency of 1 cycle per second is 1 Hz
Frequency of 2 cycles per second is 2 Hz
1 thousand cycles per second
1 kilohertz
kHz
1 million cycles per second
1 megahertz
MHz
1 billion cycles per second
1 gigahertz
GHz
1 trillion cycles per second
1 terahertz
THz
Common Frequencies
How often a vibration or wave occurs
Measured in hertz (cycles per second)
AM
1,230,000 Hz or 1,230 kHz
FM
104,700,000 Hz
104.7 MHz
Microwave
2,000,000,000 Hz
2 GHz
IR 10,000,000,000,000 Hz
10 THz
or Terahertz
13
Frequency
vs
Period
Š Vibrations per second Š Seconds for 1
(Hz)
vibration (sec)
Š 5 swings per second
(5 Hz)
5 inverse key
1 swing every 1/5 of a
second
Frequency
f = 1/T
and
Period
12
T=1/f
The Sears Tower in Chicago is 110 stories
tall.
When the wind blows, the period of time
it takes to sway back and forth once is 10
seconds.
What is it’s frequency in hertz?
10, X-1, ENTER = 0.1 Hz
12
period of 10(sec) = a frequency of 0.1(Hz)
Š So, when the Sears
Tower sways back and
forth in 10 seconds, it
will move 1/10 of a
cycle in 1 second.
Transverse- motion of
the medium is at right
angles to the direction
in which a wave
travels. Types:
liquids, EM, ropes
Longitudinal- particles
move along the
direction of the wave.
Types: sound waves
10
Parts of a Wave:
Top: Transverse
Compression
Rarefraction
Bottom: Longitudinal
Complete lecture notes 1-13
Lab Prep
Calculations Section
#1. Formula for frequency (with units)
#2. Formula for time period (with units)
Summary Section
#1. Definition longitudinal and transverse (waves)
#2. Definition frequency and period
#6. Definition amplitude
Scoring
5/5 pts
Due Today: Lab 25.1 Pendulum
3/5
1/5
Due Tomorrow: Lab 25.3