•What happens when you drop at pebble in a pond?

• Let’s see.

• A wave is the motion of a disturbance.• Particles of a wave vibrate around an

equilibrium position

• Water is a medium through which the disturbance travels.• The medium does not travel with the

wave• The medium particles stay in their

original positions

• Example:–Does a bell ring in a vacuum?

• Not all waves require a medium.–Electromagnetic waves

Waves that require a medium are called mechanical waves.

• Pulse waves- a single traveling pulse

• Periodic waves- a multiple traveling pulses

• Sine waves- wave whose source vibrates with simple harmonic motion• Special kind of periodic wave

• Transverse waves- vibrations are perpendicular to the wave’s motion• Waveform- a picture of a wave

• Transverse waves: y-coordinate represents the displacement of each point of the string at time and the x-coordinate represents the equilibrium

• Wave crest- highest point of the wave• Wave trough- lowest point of the

wave• Wavelength- the distance between 2

troughs or 2 crest

• Longitudinal wave- vibrations are parallel to the wave motion• Waveform- compressed regions

correspond to the crest of the waveform and stretched correspond to the trough

• Sound is a longitudinal wave.• All sound waves are produced by

vibrating objects.– Tuning forks, guitar strings, vocal

cords, speakers

• The vibrating object pushes the air molecules together, forming a compression.

• It then spreads them apart, forming a rarefaction.

• The diagram shows compressions (dark) and rarefactions(white). If you measured the pressure or density of the air and plotted these against position, how would the graph appear?

Click below to watch the Visual Concept.

Visual Concept

• Frequency is the number of waves per second. • You have heard of ultrasound. What is it?• Frequencies audible to humans are between 20

Hz and 20 000 Hz.– Middle C on a piano is 262 Hz.– The emergency broadcast signal is 1 000 Hz.

• Infrasound frequencies are lower than 20 Hz.• Ultrasound frequencies are greater than 20

000 Hz.

Click below to watch the Visual Concept.

Visual Concept

• V = (∆x) / (∆t)• Displacement of a wavelength occurs in a

time interval equal to one period• V = (λ)/ T• Frequency and period are inversely

proportional• f= 1/T

• Therefore, V = (λ)/T = fλSpeed of a wave = frequency X wavelength

• Wave speed of a mechanical wave is constant for any given medium

• Wave speed changes when a wave moves through different mediums

• Waves transfer energy by transferring the motion of matter rather than matter itself

• Wave transfer energy efficiently

A piano emits frequencies that range from a low of about 28 Hz to a high of about 4200 Hz. Find the range of wavelengths in air attained by this instrument when the speed of sound in air is 340m/s.

0.081 m ≤ λ≤ 12 m

An FM radio station broadcasts electromagnetic waves at a frequency of 125 MHz. These radio waves have a wavelength of 2.40m. Find the speed of the radio waves.

3.00 X 108 m/s

The speed of the radio waves in item 2 is the speed of any electromagnetic waves traveling through empty space. Calculate the wavelength of electromagnetic waves emitted at the following frequencies:

Radio Waves 88.0 MHz

3.41 m

The speed of the radio waves in item 2 is the speed of any electromagnetic waves traveling through empty space. Calculate the wavelength of electromagnetic waves emitted at the following frequencies:

Visible Light Waves 6.00 X 108 MHz

5.00 X 10 -7 m

The speed of the radio waves in item 2 is the speed of any electromagnetic waves traveling through empty space. Calculate the wavelength of electromagnetic waves emitted at the following frequencies:

X-ray Waves 3.00 X 1012 MHz

1.00 X 10 -10 m

The speed of the radio waves in item 2 is the speed of any electromagnetic waves traveling through empty space. What is the period of vibration for the following frequencies:

Radio Waves 88.0 MHz

1.14 X 10-8 s

The speed of the radio waves in item 2 is the speed of any electromagnetic waves traveling through empty space. What is the period of vibration for the following frequencies:

Visible Light Waves 6.00 X 108 MHz

1.7 X 10 -15 s

The speed of the radio waves in item 2 is the speed of any electromagnetic waves traveling through empty space. What is the period of vibration for the following frequencies:

X-ray Waves 3.00 X 1012 MHz

3.3 X 10 -19 s

A tuning fork produces a sound with a frequency of 256 Hz and wavelength in air of 1.35m.

What value does this give for the speed of sound in air?

346 m/s

A tuning fork produces a sound with a frequency of 256 Hz and wavelength in air of 1.35m.

What would be the wavelength of the wave produced by this tuning fork in water in which sound travels at 1500 m/s?

5.9 m

Sketch a pulse wave that is longitudinal.

A spring that has a single stretched region with a single compressed region

Sketch a periodic wave that is longitudinal.

A spring that has a single stretched regions with a several compressed regions

Sketch a pulse wave that is transverse.

A spring that has a single hump either above or below its equilibrium position.

Sketch a periodic wave that is transverse.

A spring that has several humps above and below its equilibrium position.

If the amplitude of a sound wave is increased by a factor of four, how does the energy carried by the sound wave in a given time interval change?

The energy will be 16 times as great.