1. 8.1: What is a Vibration?

2. Recall: The Particle Theory of Matter
All matter is made of _______________
Particles are constantly ______________
As temperature increases, particles move __________
As temperature increases, distance between particles
_______________
What state of matter does each of these images represent?

3. Vibration
Imagine a pendulum:
Point #2 represents the _____________
_____________
Points #1 and #3 are equal distances
away from equilibrium.
_________________: the cyclical motion of an object about an equilibrium point (one back and forth motion of the pendulum)

4. What’s happening to the energy of the bob as it goes through each vibration(i.e. goes through a cycle)? What if you were looking at the motion of particles instead?

5. Mechanical Wave Transfer of energy through a material due to vibration
The material is called a ___________
How long a vibration can continue in a medium depends on how much energy is gained/lost by the medium in the vibration. (usually very little)
Tighter/closer the less energy lost
More rigid = less energy lost in unintentional directions

6. Net Motion
The ________________ of a particle over a certain time interval. The difference between the particle’s initial and final positions
Net motion of particles causes the
Ideally, net motion is zero once vibration has stopped. Therefore no work is done and no energy is lost by the vibration

7. Particle Behaviour in Different Media
All vibrations need a medium to transfer the waves.
A medium’s effectiveness at transmitting vibrations depends on its
Speed and distance a wave can travel depends on the composition of the medium.
more rigid =
less rigid =

8. Particle Behaviour in Different Media
Solids
Atoms held together in crystal formation so they can only vibrate slightly
Elastic: medium returns to its original shape after being disturbed
Most solids have this property

9. Particle Behaviour in Different Media
Fluids
Liquid molecules are in contact, so they are still very effective transmitters of waves
Gases have the lowest particle density, so they are the least effective wave transmitters
Gases rely on translational motion:
The straight-line motion of a molecule

10. Types of Mechanical Waves
Transverse Waves:
Eg. Guitar string: energy flows down the string but motion is back and forth from the finger/pick plucking the string

11. TRANSVERSE WAVES

12. Longitudinal WAVES

13. Parts of a Longitudinal Wave
Compressions:
Rarefactions:

14. Sound Longitudinal waves produce sound:
Sound (and other forms of energy, too) is transmitted ONLY as a longitudinal wave in fluids, but can be either transverse or longitudinal in solids.

15. What Type of Wave?

16. Wave Characteristics Time-based characteristics: Cycle Frequency (f)
Period (T)

17. Wave Characteristics
Amplitude
Wavelength (λ)

18. Wave Characteristics Phase The x-coordinate of a particle
When the waveform has been shifted along the x-axis, this is a phase shift

19. Wave Characteristics Particles are considered to be in phase when:
Otherwise they are considered ______________

20. Homework From textbook: 8.2 Practice Questions # 1-6, 8

21. 8.4 – Determining Wave Speed

22. The Universal Wave Equation
How would you determine the speed of something…? Speed or Velocity is equal to distance/time… For a wave (Vw)… d = t =

23. Things to Note: One vibration/cycle of the source =
the frequency of the source =
If the frequency of the source never changes then the frequency of the wave doesn’t either, even if the speed and wavelength change.

24. Example 1
The wavelength of a water wave in a ripple tank is m. If the frequency of the wave is 2.5 Hz, what is its speed? G: R: A: S: P:

25. Example 2
The period of a sound wave from a piano is 1.18 x 10-3 s. If the speed of the wave in the air is 3.4 x 102 m/s, what is its wavelength? G: R: A: S: P

26. Factors That Affect Wave Speed
Temperature
Linear Density

27. Factors That Affect Wave Speed
Tension
We can combine these factors to get another equation for wave speed (giving us 3):

28. Example 3
If a string on a wave machine has a linear density of kg/m and a tension of 250 N, what is the wave speed? G: R: A: S: P:

29. Example 4
If a 2.5 m long string on the same wave machine has a tension of 240 N, and the wave speed is 300 m/s, what is the mass of the string? G: R: A: S: P:

30. Homework
8.4 Section Questions: #1- 7 Quiz on

31. 8.4 – Determining Wave Speed

32. The Universal Wave Equation
How would you determine the speed of something…?
For a wave (Vw)…

33. Things to Note: One vibration/cycle of the source =
the frequency of the source =
If the frequency of the source never changes then the frequency of the wave doesn’t either, even if the speed and wavelength change.

34. Example 1
The wavelength of a water wave in a ripple tank is m. If the frequency of the wave is 2.5 Hz, what is its speed? G: R: A: S: P:

35. Example 2
The period of a sound wave from a piano is 1.18 x 10-3 s. If the speed of the wave in the air is 3.4 x 102 m/s, what is its wavelength? G: R: A: S: P

36. Factors That Affect Wave Speed
Temperature
Linear Density

37. Factors That Affect Wave Speed
Tension
We can combine these factors to get another equation for wave speed (giving us 3):

38. Example 3
If a string on a wave machine has a linear density of kg/m and a tension of 250 N, what is the wave speed? G: R: A: S: P:

39. Example 4
If a 2.5 m long string on the same wave machine has a tension of 240 N, and the wave speed is 300 m/s, what is the mass of the string? G: R: A: S: P:

40. Homework
8.4 Section Questions: #1- 7 Quiz on

41. 8.5 Properties of Sound Waves

42. Categories of Sound Waves
Audible Sound

43. The Speed of Sound
The speed of sound in air depends on Where T is the air temperature, in °C.

44. Example
If the speed of sound is measured to be 318 m/s, what is the current air temp? G: R: A: S: P:

45. Example An aircraft is flying at 905 km/h in air at a temperature of
What is the local speed of sound? G: R: A: S: P:

46. Mach Number
It is possible for an object (e.g. aircraft, rocket) to travel faster than the speed of sound. Note: M has no units since it is a ratio.

47. Example or 83.5% the local speed of sound
b) Calculate the aircraft’s Mach number. G: R: A: S: P:
or 83.5% the local speed of sound

48. Sound Intensity Sound level Measured in decibels, dB
Logarithmic scale (not linear) → an increase of 3 dB represents a doubling of sound energy
Sounds over 100 dB that last longer than a few minutes can be harmful to hearing

52. Loudness & Distance As a sound wave expands from its source:
As a result, your ears detect a quieter sound.

53. Loudness & Distance
Amplitude is an indirect way of measuring the energy transferred.

54. Homework Practise (on pg. 393): #1-3 Practise (on pg. 394): #1-3
8.5 Questions (on page 397): #2-4, 9
Reminder:
Quiz on ch content tomorrow!
Vibrations
Wave characteristics
Types of waves