8.1: What is a Vibration?

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?

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)

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?

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

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

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 =

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

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

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

TRANSVERSE WAVES

Longitudinal WAVES

Parts of a Longitudinal Wave Compressions: Rarefactions:

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.

What Type of Wave?

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

Wave Characteristics Amplitude Wavelength (λ)

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

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

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

8.4 – Determining Wave Speed

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 =

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.

Example 1 The wavelength of a water wave in a ripple tank is 0.080 m. If the frequency of the wave is 2.5 Hz, what is its speed? G: R: A: S: P:

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

Factors That Affect Wave Speed Temperature Linear Density

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

Example 3 If a string on a wave machine has a linear density of 0.011 kg/m and a tension of 250 N, what is the wave speed? G: R: A: S: P:

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:

Homework 8.4 Section Questions: #1- 7 Quiz on

8.4 – Determining Wave Speed

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

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.

Example 1 The wavelength of a water wave in a ripple tank is 0.080 m. If the frequency of the wave is 2.5 Hz, what is its speed? G: R: A: S: P:

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

Factors That Affect Wave Speed Temperature Linear Density

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

Example 3 If a string on a wave machine has a linear density of 0.011 kg/m and a tension of 250 N, what is the wave speed? G: R: A: S: P:

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:

Homework 8.4 Section Questions: #1- 7 Quiz on

8.5 Properties of Sound Waves

Categories of Sound Waves Audible Sound

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

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

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:

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.

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

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

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

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

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. 8.1-8.3 content tomorrow! Vibrations Wave characteristics Types of waves