Chapter 8

Vibrations and Waves

Mr. JeanJanuary 3rd, 2012

The plan:

Video Clip of the dayVideo Clip of the day Introduction to waves Introduction to waves Ways to transmit & transfer energyWays to transmit & transfer energy

Welcome Back:

Things to look forward to in 2012Things to look forward to in 2012

Less end of world predictions compared to last year.: There are only 6 popular end of world There are only 6 popular end of world

theories scheduled for 2012. theories scheduled for 2012.

This is down from last year’s 9. This is down from last year’s 9.

The most popular being December 21The most popular being December 21stst, , 2012 – The end of the Myna calendar. 2012 – The end of the Myna calendar.

Total Solar Eclipse

It doesn’t happen that often !!It doesn’t happen that often !! Next year, on Next year, on November 13thNovember 13th, the Earth , the Earth

will witness a total solar eclipsewill witness a total solar eclipse

Closest known near miss: A NASA team has discovered that next year A NASA team has discovered that next year

will be our closest asteroid miss EVER.will be our closest asteroid miss EVER.

The beast in question is named ‘433 Eros‘ The beast in question is named ‘433 Eros‘ and has been haunting our skies since its and has been haunting our skies since its discovery in 1898. Come Jan 31st, if you’re discovery in 1898. Come Jan 31st, if you’re looking in the right direction, you should be looking in the right direction, you should be able to get a decent look.able to get a decent look.

Space Travel for a price: Scheduled to kick off in 2012 is COMMERCIAL Scheduled to kick off in 2012 is COMMERCIAL

SPACE TRAVEL. Yes, that’s right. Come SPACE TRAVEL. Yes, that’s right. Come October 2012, tickets will be on sale for you to October 2012, tickets will be on sale for you to get your very own space cadet feeling.get your very own space cadet feeling.

However, at a cool $200,000.However, at a cool $200,000.

And of course:

Physics 11 - Waves, light & sound.Physics 11 - Waves, light & sound.

Physics 11 – Quiz Chapter #5 & #6Physics 11 – Quiz Chapter #5 & #6

Science Fair Science Fair

Exams!!! (woohoo?) Exams!!! (woohoo?)

There are two ways to transmit information/energy in our universe:

1) Particle Motion

2) Wave Motion

Light and Sound

Both are vibrations of energy and they share some similar wave properties.

Random interesting question:

The Earth’s atmosphere is more dense than The Earth’s atmosphere is more dense than Mars. If you and your friend stand at Mars. If you and your friend stand at opposite ends of a football field. You talk opposite ends of a football field. You talk just loud enough to hear each other. If you just loud enough to hear each other. If you talked at the same volume, however you talked at the same volume, however you and your friend were on Mars what would and your friend were on Mars what would happen to your friends voice? happen to your friends voice?

How do you know?How do you know?

1. VIBRATION OF A PENDULUM

Examples: Metronome, Grandfather clock, Examples: Metronome, Grandfather clock, etc..etc..

T l g2 T is the period, the time for one vibration. l is the length of the pendulum. g is the acceleration due to gravity. (Galileo discovered this.) Period (T) is independent of the bob mass.

Pendulum Uses:

• When oscillations are small, the motion is

called simple harmonic motion and can be

described by a simple sine curve.

Simple Harmonic Motion:

Any motion that repeats itself precisely Any motion that repeats itself precisely over equal periods of time when generated over equal periods of time when generated by a linear restoring force in accordance to by a linear restoring force in accordance to Hooke’s LawHooke’s Law. .

Common Examples:

Sinusoidal equationsSinusoidal equations PendulumsPendulums Weights on a springWeights on a spring All examples of uniform circular motion with constant All examples of uniform circular motion with constant

velocities.velocities. Ferris wheelsFerris wheels Tires Tires A car turning around a circular track etc…..A car turning around a circular track etc…..

Pistons in an enginePistons in an engine Musical instrumentsMusical instruments Standing wavesStanding waves Record playersRecord players

Piston Example:

SHM: Tarzan / Grandfather Clock

2. WAVE DESCRIPTION

Frequency ( f ) is the number of vibrations per

unit of time made by the vibrating source.

Units - cycles per second

1/s

Hertz (Hz)

Picture of a Transverse Wave

CrestCrest

TroughTrough

WavelengthWavelength

AA

A - AmplitudeA - Amplitude

Distance between adjacent crests in a

transverse wave.

Distance a wave travels during one vibration.

in meters

Wavelength ()

The period (T) of a vibration is the time

required to make one vibration.

The The period (T) of a wave is the time (T) of a wave is the time

required to generate one wave. required to generate one wave.

It is also the time required for the wave to It is also the time required for the wave to

travel one wavelength. travel one wavelength.

FrequencyFrequency PeriodPeriod

ionsec/vibrat21

ionsec/vibrat31

ionsec/vibrat41

ionsec/vibrat2

ionsec/vibrat1

/secvibrations3

secvibration/1

/secvibrations4

ecsvibration21 /

/secvibrations2

FrequencyPeriod

1

Example Question: A mass suspended from the end of a spring A mass suspended from the end of a spring

vibrates up and down 24 times in 36 vibrates up and down 24 times in 36 seconds. What is the frequency and period seconds. What is the frequency and period of the vibration? of the vibration?

In class work:

Read PagesRead Pages P. 345 - 353P. 345 - 353