C-25 Warm-Up Question: What do pendulums, springs and waves have in common?

They all exhibit periodic or simple harmonic motion!

A swinging pendulum or bouncing spring creates a wave or sine curve.

4 & 8

Pendulum Motion

The back and forth motion (vibrations or oscillations) of a swinging pendulum is called simple harmonic motion.

The restoring force is proportional to the displacement from equilibrium.

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.

2

Examples of Waves and Vibrations:

Swings of a pendulum, trees in the windWaves in a lakeElectrons vibrating in an antennaSounds from voices, music, natureLight, x-rays and other energy (EM waves)(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.

Parts of a Wave

1-crest2-trough3-wavelength(lambda-λ)

4-amplitude---equilibriumNodeAntinode 3

4

2

1

9

Frequency is measured in Hertz (Hz)

Frequency of 1 cycle per second is 1 HzFrequency 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 occursMeasured in hertz (cycles per second)

AM 1,230,000 Hz or 1,230 kHzFM 104,700,000 Hz 104.7 MHzMicrowave

2,000,000,000 Hz 2 GHzIR 10,000,000,000,000 Hz 10 THz

or Terahertz

Frequency vs Period

Seconds for 1 vibration (sec)

1 swing every 1/5 of a second

Vibrations per second (Hz)

5 swings per second (5 Hz)

5 inverse key

13

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?

Frequency and Period

f = 1/T T=1/f

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10, X-1, ENTER = 0.1 Hz period of 10(sec) = a frequency of 0.1(Hz)

So, when the Sears Tower sways back and forth in 10 seconds, it will move 1/10 of a cycle in 1 second.

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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:

Bottom: LongitudinalRarefractionCompression

Top: Transverse

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 3/5 1/5Due Today: Lab 25.1 Pendulum Due Tomorrow: Lab 25.3