Chapter 8 - SPH 3U1

Vibration

A cyclical motion of an object about an equilibrium position

Ex:

• The pendulum going back and forth

Equilibrium Point

The position in which the object is in the same position as rest

Mechanical Waves

The transfer of energy through a material due to vibration.

Medium

The material that permits the transmission of energy through vibrations

Net Motion

The displacement of a particle over a certain time interval; the difference between particle’s initial and final positions

Elastic

Property of a medium that returns to its original shape after being disturbed

Translational Molecular Motion

Straight-line motion of a molecule; this motion is typical of gases because the particles in liquids and solids are not free to move in this manner

Waves in Solid Mediums

Transfers waves efficiently —> Waves go far and fast

Waves in liquids and gases

Less efficient compared to solids

• Liquids > Gasses —> Waves transfer better in the water

• Gasses usually only use translational movement —> Net Motion ≠ 0

Transverse Wave

A wave in which particles vibrate perpendicular to the direction of the flow of energy

• Ex: A string moving up and down

Longitudinal Wave

A wave in which particles vibrate parallel to the direction of the flow of energy

• Ex: A slinky

Compression

The region in a longitudinal wave in which the medium’s particles are closer together

Rarefractions

Region in a longitudinal wave in which the medium’s particles are farther apart

Sound

A form of energy produced by rapidly vibrating objects detectable by the ear

Amplitude

Maximum displacement of a wave from its equilibrium point

Waveform

Shape of a wave when graphed

Crest

Maximum point of a transverse wave

Trough

Minimum point of a transverse wave

Wavelength

Distance between 2 similar points in successive identical cycles in a wave.

• Crest to Crest

• Trough to Trough

Phase

A continuous transverse or longitudinal wave, the x-coordinate of a unique point of the wave

Phase shift

A shift of an entire wave along the x-axis with respect to an otherwise identical wave

In-Phase

The state of 2 identical waves that have the same shift

Out of Phase

State of 2 identical waves that have different phase shifts

Frequency (Hz)

Number of complete cycles that occur in unit time

Period

Time for a vibrating particle to complete one cycle

Formula for Frequency

Wave Speed

Rate at which a wave is travelling through a medium

Simple Harmonic Motion (SHM)

Any motion that repeats itself at regular intervals

Universal Wave Equation

A trumpet produces a sound wave that is observed travelling at 350 m/s with a frequency of 1046.50 Hz. Calculate the wavelength of the sound wave.

Factors that Affect Wave Speed

Temperature:

• Colder temperatures result in slower-moving molecules

• Hotter temperatures result in faster-moving molecules

Linear Density and Tension

Linear Density is how much force is needed to make the string vibrate (kg/m)

• µ = Linear Density

• m = Mass

• L = length

Wave Speed with Tension

On your class wave machine, you have a string of mass 350 g and length 2.3 m. You would like to send a wave along this string at a speed of 50.0 m/s. What must the tension of the string be?

Audible Sound Waves

Sound waves within the range of human hearing: 20 Hz to 20 kHz

Infrasonic Waves

Sound waves with frequency below 20 Hz

Ultrasonic Waves

Sound waves with a frequency above 20 kHz

Speed of Sound

Mach Number

Sound Intensity

Amount of sound energy being transferred per unit of area; measured in W/m²

Decibel

The unit of sound level used to describe the sound intensity level

• The difference between sound intensities of 10^-12 W/m² and 10^-8 W/m² is 10,000 units. This is equivalent to 40 dB or 4 B