Doppler Effect, Bow Waves, and Shock Waves - PowerPoint PPT Presentation

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Doppler Effect, Bow Waves, and Shock Waves. Doppler Effect. ~apparent change in frequency of a wave due to the motion of the source of the wave. If the object is moving towards the observer the frequency will appear to increase

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Doppler Effect, Bow Waves, and Shock Waves

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Doppler Effect, Bow Waves, and Shock Waves

Doppler Effect

• ~apparent change in frequency of a wave due to the motion of the source of the wave.

• If the object is moving towards the observer the frequency will appear to increase

• If the object is moving away from the observer the frequency will appear to decrease

Why does this happen

• Frequency- number of waves to pass by in a second.

• Waves travel out from their source in rings, like when a stone is thrown in a pond.

This person should have the same number of waves hitting them each second

As this person

Will.

But if the source is moving

• Each new wave will start in a different place than the last wave.

Each dot shows the

where the source was

when that wave was

This person now has less waves hitting them each second

than this person

Will.

. . . . . . . .

Observable traits of frequency

• Sound frequency is observed as the pitch.

• High frequency high pitch (dentist drill), low frequency low pitch (bass drum)

• Light frequency is color

• Low freq- Red OYGBI violet- high freq

Moving towards

Moving away from

With Light…

• It causes red shift (moving away from you) and blue shift (moving towards you) in stars.

• But with out an extremely high speed it is not noticeable to the human eye

• You need sensitive equipment to notice a frequency change

• Like Dual Doppler XL or Doppler 2000

• With this radar you can check the motion of a storm

What if an object is moving faster than the waves they are producing

The front edge of the

New wave will be

Wave!

here

It also creates

This pattern

Of strong

Waves at the

edges

By strong I mean

Larger amplitude

A whole bunch of waves

Hit at once causing constructive interference

And here

Where does this occur

• Two dimensionally this is called a Bow Wave.

• It commonly occurs on a speed boat

• Three dimensionally this is called a Shock Wave.

• It occurs in supersonic jets (ones that go faster than the speed of sound)

• When that strong wave hits you, you hear a sonic boom (all of the sound hitting you at once)

Sound Barrier

• There is an actual “barrier” to moving at the speed sound.

• When you hit the speed of sound (or any wave you are making) you hit all of those waves you just made.

• All of that interference causes a turbulence.

• This goes away if you are moving faster than sound.

• A sonic boom is heard by observers whenever an object moves faster than sound not just when it crosses the threshold