Today: Notes about quiz; Oscillations, Waves, Doppler effect

Quiz #2 due Thursday

Exercises due Tuesday(To be assigned for this week’s material)

Waves by hb19 on flickr

Results of first quizTHANK YOU to those students who took the quiz!

Brownian motion clicker question

Scanning Tunneling Microscopy -- pseudocolor

6. Scanning Tunneling Microscopy, color  

  Scanning Tunneling Microscopy: Think of those pretty pictures we looked at in class of iron atoms on an atomically flat copper surface.

Q: Why are different parts of the image different colors than others?

a. Different elements emit different colors of light.

b. The color of the light detected by the microscope depends on the distance between the tip and the surface.

c. The colors were invented by the IBM scientists to make the easier to make sense of (pseudocolor).

Self-sustaining oscillations are usually energy flowing from one form to another, back and forth

What are some common oscillations we can think of?

Students 2008: Electromagnetic; vibration of vocal cords or speaker; water surface; pendulum; mass on a spring; motion of a piston in an engine; atom oscillating

Are there two forms of energy that you can identify?

Mass on a spring…oscillation has a frequency and an amplitude

Frequency (hertz) = number of cycles per secondPeriod (seconds) = time per cycle (inverse of frequency)

Amplitude (often height) = magnitude of oscillation(Tricky!)

Oleg Alexandrovwikipedia

Amplitude is displacement from equilibrium

Oscillations are a foundation of wavesthey can easily be visualized as waves

User:Evil_saltinewikipedia

Oleg Alexandrovwikipedia

A wave is a disturbance that propagates through space…it carries energy from one place to another.

The author of the book says:

“The source of all waves—sound, light or whatever—is something that is vibrating.” (“Oscillating”)

This is a pretty good definition, but sometimes it’s not obvious or evident what source is “oscillating”

For our purposes, the waves we care about must propagate through space and carry energy

We also think about waves that don’t carry energy…examples?

Let’s brainstorm on waves that carry energy

…Microwaves, sound waves, light waves, radio waves, ocean waves, heat waves (infrared), gamma rays, x-rays, earthquake waves (seismic), gravitational waves,

Kinds of waves in physics

Sound wavesSeismic waves (infrasound); audible sound; ultrasonic waves

Electromagnetic wavesRadio waves; microwaves; infrared; Visible light; ultraviolet; x-

rays; gamma rays

“Other” wavesWind-driven ocean waves; ripples in a pond;

waves in the demos today; waves in other fluids (see picture)

Matter waves

Gravitational Waves

http://www.3sigma.ca/gravityWaves.html

Wave has properties of an oscillation (frequency and an amplitude) plus speed and wavelength

Frequency (hertz) = number of cycles per secondPeriod (seconds) = time per cycle (inverse of frequency)

Amplitude (often height) = magnitude of oscillation

Speed (meters per second) = how quickly energy propagates through space

Wavelength (meters) = distance between repeated features.

http://www.3sigma.ca/gravityWaves.html

Frequency and speed are the fundamental properties of a wave

The frequency of the wave is determined by the frequency of the driving oscillation.

The speed of the wave is determined by the physics.

The wavelength (e.g. distance between crests) is determined by the frequency and speed.Wavelength =

Wave speed

frequency

(Wave speed = wavelength x frequency)

Wave table demoFrequency is fundamentalEnergy transfer

Clicker Question—Properties of waves

What is described incorrectly in this picture?

a)Wavelengthb)Amplitudec) Frequencyd)period

Clicker Question—Properties of waves

What is described incorrectly in this picture?

a)Wavelength (this is really common…see figure 19.3 in

textbook)b)Amplitudec) Frequencyd)period

Ripple tank experiments with speed, frequency, wavelength

http://www.falstad.com/ripple/ (linked on WebCT)This is really worth trying out!Google search for: ripple appletThis simulation is based on physics

Clicker question

I am going to decrease the frequency of the oscillating source. What will happen to the wavelength?

A. NothingB. Wavelength will increaseC. Wavelength will decreaseD. Impossible to determine

http://www.falstad.com/ripple/

Clicker Question—Wavelength, frequency, speed

Suppose the wave speed is fixed for all frequencies and wavelengths. Which has a longer wavelength?

a)Frequency = 770,000 Hertzb)Frequency = 97,300,000 Hertzc) Both are the same, since speed is fixed

Clicker Question—Wavelength, frequency, speed

Suppose the wave speed is fixed for all frequencies and wavelengths. Which has a longer wavelength?

a)Frequency = 770,000 Hertzb)Frequency = 97,300,000 Hertzc) Both are the same, since speed is fixed

Wave speed = wavelength x frequency

Wavelength =Wave speed

frequency

Transverse Waves and Longitudinal Waves

Transverse waves:“Motion of the medium” is perpendicular to the

direction of wave propagationE.g. Ocean waves

Longitudinal waves:“Motion of the medium” is in same direction as

direction of wave propagationE.g. compression waves in slinky; SOUND

Transverse wave demo

From Zhang Jiang (our TA):The speed of longitudinal waves and transversal waves differIf there is an earthquake you will feel the vertical shake before the horizontal shake

Key concepts:

1. Waves transmit energy, not the material that is waving

2. If a transmitter and receiver are not moving relative to each other then:Frequency observed = frequency

transmitted

Doppler effect

Frequency observed NOT equal to frequency transmitted!

Because source and receiver are moving relative to each other

Ripple tank Doppler

Doppler demo

Clicker Question to think about:Wind and Doppler Effect

Does the wind affect the pitch of a factory whistle you hear on a windy day?

1. Yes2. No