Physics 11 Advanced:

Mr. JeanMr. Jean May 15May 15thth, 2012, 2012

The plan: Dates for TestDates for Test Review of yesterdayReview of yesterday

Constructive & Destructive InterferenceConstructive & Destructive Interference Fixed EndsFixed Ends Open endsOpen ends Waves when they meetWaves when they meet

What makes a good surfing dayWhat makes a good surfing day Visible spectrumVisible spectrum Doppler EffectDoppler Effect Shock WavesShock Waves Return Pendulum Lab Return Pendulum Lab Speed of sound Lab soon!Speed of sound Lab soon!

Unit Test:

Chapter #5, 6 & 7Chapter #5, 6 & 7 May 31May 31stst, 2012, 2012 Period #4Period #4

Test Outline:

Chapter #5Chapter #5 InertiaInertia Newton’s Second LawNewton’s Second Law Newton’s Third LawNewton’s Third Law 2d applied forces2d applied forces Inclined planesInclined planes Momentum part #1Momentum part #1

Test Outline: Chapter #6Chapter #6

WorkWork EnergyEnergy

KineticKinetic ElasticElastic PotentialPotential Gravitational potentialGravitational potential

Work Energy TheoremWork Energy Theorem Power and EfficiencyPower and Efficiency

Test Outline: Chapter #7:Chapter #7:

Energy transformationEnergy transformation PendulumPendulum SpringSpring Conservation of energyConservation of energy Conservation of momentumConservation of momentum

CollisionsCollisions RecoilRecoil Glancing blowsGlancing blows

Test Format:

20-30 points for Multiple Choice20-30 points for Multiple Choice 20-30 points for True & False20-30 points for True & False 30-50 points for Long Answers30-50 points for Long Answers

Return Labs:

Comments about labsComments about labs

Constructive & Destructive Interference:

+ =

Const r uct ive int er f er ence

+ =

Dest r uct ive int er f er ence

cancellat ion

When waves meet: v v

v

v

M ee tin g w avesou t o f ph ase

M ee tin g w avesin o f ph ase

Standing Waves: 1

2

3

4

5

6

7

8

Tim e L a pse View o f S tan d in g W ave

Waves and Wave Length:

The standing wave to the The standing wave to the left represents one half of left represents one half of the wavelength of the the wavelength of the wave or ½ wave or ½ . .

This would be a complete This would be a complete wave cycle or 2/2 wave cycle or 2/2 or 1 or 1 ..

This would be 3/2 This would be 3/2 or 1 or 1 ½ wave.½ wave.

Fundamental Frequencies:

fu n d a m e n ta l fr e q u e n c y1 s t h a rm o n ic

2 n d h a rm o n ic

3 rd h a rm o n ic

Interference is a characteristic of all waves.

Standing Waves When two sets of waves of equal amplitude

and wavelength pass through each other in opposite directions, it is possible to create an interference pattern that looks like a wave that is “standing still.” It is a changing interference pattern.

Demo - Rope and strobeDemo - Rope and strobe Demo - Mechanical overhead modelDemo - Mechanical overhead model

Visible Spectrum:

DOPPLER EFFECT

Refers to the change in frequency when there is

relative motion between an observer of waves and

the source of the waves

Doppler Movie - Doppler Movie - URL

When a source of waves and an observer of When a source of waves and an observer of waves are getting closer together, the observer waves are getting closer together, the observer of the waves “sees” a frequency for the waves of the waves “sees” a frequency for the waves that is higher than the emitted frequency.that is higher than the emitted frequency.

When a source of waves and an observer of When a source of waves and an observer of waves are getting farther apart, the observer waves are getting farther apart, the observer of the waves “sees” a frequency for the waves of the waves “sees” a frequency for the waves that is lower than the emitted frequency.that is lower than the emitted frequency.

All waves exhibit the Doppler effect.

A particularly interesting example is used by

astronomers to determine if light emitting objects

(such as stars) are getting closer to us or farther

away.

On average most stars are moving farther away,

and their light spectra are “red shifted.”

Red Shift: Moving Away from sourceRed Shift: Moving Away from source

Actual Visual SpectrumActual Visual Spectrum

Observed Visual SpectrumObserved Visual Spectrum

Blue Shift: Moving towards sourceBlue Shift: Moving towards source

Actual Visual SpectrumActual Visual Spectrum

Observed Visual SpectrumObserved Visual Spectrum

Radar bounced off a spinning planet can

exhibit a Doppler effect and lead to a

determination of the spin rate of the planet.

This was used to discover that Venus has a This was used to discover that Venus has a

retrograde spin.retrograde spin.

Of course police use the Doppler effect to Of course police use the Doppler effect to

catch speeding motorists.catch speeding motorists.

BOW WAVES

Waves in front of moving object pile up. The familiar bow wave generated by a

speedboat knifing through the water is a non-periodic wave produced by the overlapping of many periodic circular waves. It has a constant shape.

Video Demonstration:

Demo 2.1 – Waves & Wake from Phys123Demo 2.1 – Waves & Wake from Phys123

SHOCK WAVES

Just as circular waves move out from a swimming bug, spherical waves move out from a flying object. If the object flies faster than the waves, the result is a cone-shaped shock wave.

There are two booms, one from the front of the flying object and one from the back.

Video Demonstrations:

- slower than the speed of soundSubsonic

Supersonic - faster than the speed of sound

Mach Number = speed of sound

speed of object

Speed of sound lab soon:

Good Surf Days:

There are two main factors that determine There are two main factors that determine how good the surf will be. how good the surf will be. First, there are the conditions that lead to initial First, there are the conditions that lead to initial

wave formation. These determine the quality wave formation. These determine the quality and size of the ground swell that will hit the and size of the ground swell that will hit the surf spot. surf spot.

The second main factor is the local conditions The second main factor is the local conditions at the surf spot. These have to be right to ensure at the surf spot. These have to be right to ensure the swell can create quality waves. Let's look at the swell can create quality waves. Let's look at both of these factors in turn. both of these factors in turn.

Factors which produce waves:

There are three main factorsThere are three main factors Wind Speed - The greater the wind speed the Wind Speed - The greater the wind speed the

larger the wave. larger the wave. Wind Duration -The longer the wind blows the Wind Duration -The longer the wind blows the

larger the wave. larger the wave. Fetch - The greater the area the wind affects the Fetch - The greater the area the wind affects the

larger the wave. larger the wave.

Closely packed isobars (areas of equal pressure Closely packed isobars (areas of equal pressure shown on a weather map) mean strong winds. It is shown on a weather map) mean strong winds. It is these deep low pressures that generate the big these deep low pressures that generate the big swells. The swell will be bigger and last longer... swells. The swell will be bigger and last longer...

Making the waves: How Waves Are MadeHow Waves Are Made

Waves are generated by wind. Offshore storms generate Waves are generated by wind. Offshore storms generate winds which blow on the surface of the sea and create winds which blow on the surface of the sea and create ripples, much in the same way as the ripples in your post ripples, much in the same way as the ripples in your post surf cuppa are made when you blow on it to cool it down. surf cuppa are made when you blow on it to cool it down.

Where it all begins: Where it all begins: Offshore storms generate winds. Offshore storms generate winds. The ocean would be almost completely flat without wind. The ocean would be almost completely flat without wind.

The stronger and longer the wind blows, the more The stronger and longer the wind blows, the more effect it has on these ripples and the larger they effect it has on these ripples and the larger they become. Initially the waves will just be small chop, become. Initially the waves will just be small chop, but these will soon increase in size. but these will soon increase in size.

As the wind continues to blow and the waves generated remain under As the wind continues to blow and the waves generated remain under the influence of the wind, the smaller waves will increase in size. The the influence of the wind, the smaller waves will increase in size. The wind will get hold of the small waves much more easily than the calm wind will get hold of the small waves much more easily than the calm sea surface. sea surface.

The wave size is dependent on the wind speed generating it. A certain The wave size is dependent on the wind speed generating it. A certain wind speed will only be able to generate a wave of certain size. Once wind speed will only be able to generate a wave of certain size. Once the largest waves that can be generated for a given wind speed have the largest waves that can be generated for a given wind speed have formed, the seas are "fully formed." formed, the seas are "fully formed."

The longer period waves are faster and move The longer period waves are faster and move farther ahead of the rest of the slower waves. farther ahead of the rest of the slower waves.

As the waves travel farther away (propagate) As the waves travel farther away (propagate) from the wind source, they start to organise from the wind source, they start to organise themselves into swell lines. themselves into swell lines. Swells are essentially "Wave trains"Swells are essentially "Wave trains"

When everything is right:

Nova Scotia

Nova Scotia is quickly becoming a surf Nova Scotia is quickly becoming a surf destination for surfers around the world. destination for surfers around the world. Especially late August into October for Especially late August into October for

hurricane season. hurricane season.