1. WAVES A Description of the Phenomenon of Energy Movement OR
Periodic Motion & VIBRATIONS aka Simple Harmonic Motion

2. Simple harmonic motion periodic motion where the unbalanced force varies directly with the displacement from the equilibrium point; this motion is described by the period, the frequency, and the amplitude of the motion – example: A Pendulum
Period (T) the time in seconds needed to complete one cycle of motion Amplitude the distance from the equilibrium point to the point of greatest displacement

3. frequency the number of vibrations in a time interval; its SI unit is hertz (Hz)
I like to use the Greek letter, f , as the symbol for frequency. This can be confusing to students since its appearance is similar to the letter f . 1 Hz = 1 sec-1 T = 1/n or T = 1/f

4. Waves and Vibrations

5. Waves transport energy, not particles.
Wave Motion
Waves transport energy, not particles.
Imagine a fishing bobber floating on top of the water. As water waves pass, the bobber may move up and down, but it stays in the same horizontal location.

6. BASIC WAVE CLASSIFICATIONS
1. MECHANICAL WAVES -
type of energy transfer involving some sort of medium - matter through which the wave energy moves.
The wave energy causes the particles to move or vibrate, but not move along with the wave itself.
EX: water, sound, earthquake waves

7. 2. ELECTROMAGNETIC WAVES -
This type of waves does not need any matter medium to travel through - travels at the speed of light. These waves are defined as periodic disturbances of an electromagnetic field.

8. Notice the wide variety of waves in the EM spectrum!

9. Ex: water waves, waves in a rope...
HOW DO WAVES MOVE?
TRANSVERSE - this wave type vibrates the particles or field through which they pass at right angles to the direction of wave motion.
Ex: water waves, waves in a rope...

10. LONGITUDINAL - this wave type vibrates the particles or field through which they pass parallel to the direction of wave motion.
Ex: sound waves

11. WAVE PARTS/CHARACTERISTICS
Crest - top of wave
Trough - bottom of wave
Wavelength - distance between 2 successive crests or troughs symbol = 
Wave Fronts - a locus of adjacent points that are in phase

12. Amplitude - maximum height or depth of wave from midpoint -also a measure of the amount of work a wave can do or its ENERGY
Frequency - the number of waves that pass a fixed point in a given amount of time - usually per second - # of waves or cycles/s = HERTZ - kHz Hz mHz - 1 X 106 Hz

13. Wave Period - the amount of time it takes for 1 complete cycle to pass a fixed point.
T = 1 / f

14. 1. The wavelength of the wave is ______.
2. The amplitude of the wave is _____.

15. wave speed = wavelength x frequency v = λ f
Generic wave speed formula that holds true for all types of waves:
wave speed = wavelength x frequency
v = λ f
λ = Greek letter “lambda”, represents wavelength.

17. An Example:
You may have used a 900 MHz cordless phone. These waves travel at the speed of light, 3 x 108 m/s. What is the period and wavelength of these cordless phone waves?
To get the wavelength:
v = 3 x 108 m/s ; f = 9 x108 Hz
v = λ f
3 x 108 m/s = λ (9 x108 Hz)
λ = .33 m
To get the period:
T = 1/f
T = 1/ (9 x 108 Hz)
T =1.1 x 10-9 sec

18. WAVES QUIZ
1. LABEL ALL CRESTS & TROUGHS
2. USE YOUR RULER TO DETERMINE THE
AMPLITUDE AND WAVELENGTH.
3. HOW MANY WAVELENGTHS ARE
REPRESENTED IN THIS DIAGRAM?

19. Waves Quiz
1. If it takes 10 s for the wave to reach point A:
a.)What is the Wavelength?
b.)What is the Amplitude?
c.)What is the Frequency?
d.)What is the Period?
e.)What is the Wave Speed?

20. Waves Quiz
1. What are the differences/similarities between:
a.) Mechanical vs. Electromagnetic Waves
b.) Transverse vs. Longitudinal waves

21. The Dynamics of the Motion of Sound Energy through Matter

22. Sound waves are longitudinal waves produced by variations in air pressure.

23. The energy of a sound wave travels away from the source through a series of molecule collisions parallel to the direction of the wave.
Tuning fork

24. Sound does not consist of air moving towards us in bulk; BUT A WAVE OF ENERGY CAUSING THE MOLECULES OF AIR TO VIBRATE - TRANSFERRING ENERGY

26. This is what you
would see on an
oscilloscope!!

27. 343 m/s is for 20oC and 1 atmosphere.
Speed of Sound:
Although we usually use 343 m/s for the speed of sound, this number varies because of a variety of factors. Note: check your reference tables!
Wind, temperature, and humidity are all factors that influence the speed of sound.
343 m/s is for 20oC and 1 atmosphere.

28. Gas molecules less tightly packed H2O molecules more tightly packed
Other Media:
Sound does not only travel in air. In fact, sound travels faster through most solids or liquids compared to air. The collisions travel better in more dense media.
Gas molecules less tightly packed
H2O molecules more tightly packed

29. SOUND TRAVELS @ Approx 340 m/s (at rm temp) - IN AIR!
At normal atmospheric pressure, the temperature dependence of the speed of a sound wave through air is approximated by the following equation:
v = 331 m/s + (0.6 m/s/C)*T
Sound waves can also travel through liquids and solids.
SOUND TRAVELS in water is 1480 m/s or 4856 ft/s. - More than 3000 miles per hour.

30. Velocity of sound varies as the inverse of the square root of the density of the medium it is in. The speed also then will depend on the temperature of the medium too. For steel is it about 4870 m/sec.
Unlike light, sounds needs some kind of material to propogate through. In a vacuum there is nothing, so sound cannot go through a vacuum.

31. Measuring sound waves
The frequency of a sound wave is called pitch.
The human ear is able to feel frequencies between 20 Hz to 20,000 Hz, depending on the age of the person.

32. The amplitude or volume of a sound wave is the amount of pressure exerted by a sound source to air molecules.
The pressure is measured by the intensity of the sound. In dB’s or decibels!!
Decibel chart

33. Pitch: Pitch is equivalent to frequency. high pitch = high frequency
low pitch = low frequency
1000 Hz
1500 Hz
2000 Hz

34. Human Hearing: The Animals:
Most humans hear approximately 20Hz through 20,000 Hz. Although this may diminish with age.
The Animals:
As you may know, many animals have higher or lower ranges to their hearing compared
to humans.

35. Beyond the Limits:
Sounds of a higher frequency than we can hear are called ultrasonic. ( ultraviolet is higher frequency than violet light)
Sounds of a lower frequency than we can hear are called infrasonic. (infrared is lower frequency than red light)

36. Nature of Sound in Air:
Sound is simply a longitudinal wave carrying energy that our ears detect.

37. When sound reflects off a surface, we call it an echo.
Reflection of Sound:
When sound reflects off a surface, we call it an echo.

38. Animal Reflections:
Bats and dolphins emit sound that is reflected off objects. The reflected sound is received by them and allows them to “see” their environment.

39. You might get this in a large hall that has no sound dampening.
Reverberations:
When many sounds echo many times off multiple surfaces, that is called a reverberation.
You might get this in a large hall that has no sound dampening.

40. Sometimes at night you can hear very distant objects...
Refraction of Sound:
Since sound travels at different speeds in various temperatures of air, sound can bend if there is a layer of different temperature air.
Sometimes at night you can hear very distant objects...

41. Tuning Forks:
A tuning fork provides a continuous push or vibration that creates a particular frequency.
Although you may not be able to see it, the tines actually do move back and forth.
As you may have noticed, the length of the tuning fork helps determine the frequency of its vibration.

42. When you lightly tap a crystal glass, you hear its natural frequency.
Any elastic material object will vibrate at one particular natural frequency.
When you lightly tap a crystal glass, you hear its natural frequency.
When an object is forced to vibrate, and this vibration matches its natural frequency, you have resonance.
It is constructive interference since the repeating waves of the natural frequency add up to produce a larger wave.

43. Swing Analogy:
Imagine starting to push someone on a swing. You need to push them at just the right time, so that their amplitude continually increases.
A certain bridge was unlucky enough to have its natural frequency match the wind frequency at that location. These wind waves constructively interfered and produced a large enough wave to completely destroy the bridge!

44. Note: a node at closed end, antinode at the open end.
Closed Tubes:
With a closed tube, resonance occurs at only certain lengths: odd 1/4 multiples of λ
Note: a node at closed end, antinode at the open end.
5/4 λ
3/4 λ
1/4 λ

45. Also called - CONSTRUCTIVE
INTERFERENCE

46. Also called - DESTRUCTIVE
INTERFERENCE

47. You get beats, a periodic variation in amplitude.
A strange effect happens when you add waves that are just slightly different frequencies.
You get beats, a periodic variation in amplitude.
The two top waves add together, superimpose, to produce the bottom pattern...

48. A stationary source of waves would produce concentric wave circles:
Doppler Effect
A stationary source of waves would produce concentric wave circles:

49. It is often observed as a car horn, or siren passes you.
A moving source would create waves that are centered closer to the direction of movement.
The Doppler effect is a shift in frequency due to a moving source or receiver.
It is often observed as a car horn, or siren passes you.

50. Police use the doppler effect to detect speeders
Police use the doppler effect to detect speeders. When the waves bounce off the oncoming car, its frequency is shifted. This is used to calculate a speed.

51. Objects that are receding are said to be red shifted.
Astronomers use the doppler shift of light from distant galaxies to learn about their motions.
Objects that are moving towards the observer are said to be blue shifted.
blue = higher frequency.
Objects that are receding are said to be red shifted.
red = lower frequency.

52. The “V” shape of these overlapping waves is called a bow wave.
Shock Waves:
As a source of waves nears the actual speed of the waves it produces, those waves “pile up”.
The “V” shape of these overlapping waves is called a bow wave.

53. Sonic Boom:
When an airplane flies faster than sound, a continuous loud rumbling is created (sonic boom).
Other examples of sonic booms include a cracking whip, and a supersonic bullet.

54. A 20mm shell flying at 500 m/s. Notice the shock waves produced.
The exposure was only 20 nanoseconds!