Frequency Determines Pitch

Sect. 16-2

3 Min. Warm-up Decide if these statements are true.

If not true, correct them. In a longitudinal wave, the vibrations

move perpendicular to the direction of the wave.

Sound is a type of electromagnetic wave.

Vibrations pass through many parts of the ear, not just the eardrum.

3 Min. Warm-up Decide if these statements are

true. If not true, correct them. In a longitudinal wave, the vibrations

move in the same direction as the wave.

Sound is a type of mechanical wave Vibrations pass through many parts of

the ear, not just the eardrum. True

Pitch The quality of the highness or lowness of a

sound. Determined by frequency Very fast vibrating object produces high

sound Slow vibrating objects produces a low sound High frequency makes high sound Low frequency makes low sound

Explore Pitch Why does the sound change?pg.

525 What happened to the sound as

you slid the ruler back? Describe the motion of the ruler.

Explore Pitch Why does the sound change?pg. 525 What happened to the sound as you slid

the ruler back? The sound became higher

Describe the motion of the ruler. The ruler moved up and down a greater distance when the ruler extended farther than when it was pulled back on the desk

Vocabulary Hertz – unit for measuring frequency and

pitch; one complete wave per second Ultrasound – sound waves in the range

above 20,000 hertz Resonance – strengthening of a sound

wave when it combines with an object’s natural vibration.

Doppler Effect – the change in observed pitch that occurs when the source or the one who hears a sound is moving.

Sound is a type of mechanical wave. Why?

It transfers energy through a medium.

It is produced by a vibrating object and travels through matter

The disturbances that travel in a sound wave are vibrations.

How is frequency related to pitch? The higher the frequency of the

sound wave, the higher pitched the sound.

Which instrument makes the lower pitched sound?

A flute A tuba

Which instrument makes the lower pitched sound?

A tuba

High and Low Frequencies

Frequency is a measure of how often a wave passes a fixed point in a certain amount of time.

One complete wave is also called a cycle

Hertz = 1 cycle or wavelength/second

A wave with a frequency of 4 hertz has 4 cycles per second

Frequency Range of Most People with Good Hearing 20 – 20,000 Hertz

Infrasound wavesSound waves with frequency below 20 Hertz. They have very long wavelengths and can travel great distances

without losing much energy.

Ultrasound Sound waves above 20,000 hzHumans cannot hear it.Many animals can hear it.

Natural Frequencies

You may see a piano tuner tap a tuning fork against

another object. The tuner does this to make the fork

resonate at its natural frequency. He tunes the

piano strings to match it.

Resonance

Causes sound waves to strengthen

Results from adding the amplitude of a sound wave to the amplitude of an object’s natural vibration

Resonance cont. When a tuning fork is struck, a

nearby tuning fork with the same natural frequency will also vibrate because of resonance.

Sound Quality A. Timbre

1. Most sounds are a combination of waves.

2. The combination of pitches is the main factor affecting the quality of sound

Pitch that you hear is called fundamental pitch

Higher-frequency pitches are called overtones This is why two singers can sound very

different when singing the same note.

Sound Quality B. The way a sound starts and

stops 1. The sound of cymbals blast out

suddenly 2. The sound of the human voice

starts much more gently.

What two factors affect sound quality?

What two factors affect sound quality? Overtones - Combination of pitches The way the sound starts and

stops

The motion of the source of a sound affects its pitch.

If an ambulance passed you, would you hear the same sound the whole time? Why or Why not?

The motion of the source of a sound affects its pitch.

No, the ambulance blasts the same pitches the whole time, but the pitch falls as the ambulance drives away.

Doppler Effect The change in perceived pitch that

occurs when the source or the receiver of a sound is moving.

How does the motion of a sound source affect its pitch? If a sound moves toward the

listener, the pitch rises. If it moves away from the listener, the pitch lowers.