Unit 31 – The Properties of Sound

Sound

Sound is a longitudinal wave that is produced by a source that vibrates.

Sound travels at different speeds in different materials and at different temperatures.

Sound will travel faster at higher temperatures than it will at lower temperatures.

Sound will also travel faster in denser or elastic materials.

Wave Speed Continued

Waves travel further and faster underwater than in air.

Waves can travel 770 mph in air (Speed of Sound)

Waves trailed 3,300 mph in water

Waves go over 10,000 mph in the ground during earthquakes

Wave Speed

Waves go faster based on the density of their medium because the tighter packed the molecules, the easier it is to transfer their energy to each other.

Pitch: The frequency of a sound wave

Musicians are concerned with the pitch of sounds

Larger vibrations make lower sounds and vice versa.

Big instruments like tubas are deep, while trumpets are higher pitched.

Question 1

Which medium would transfer sound waves the slowest?

A. Freshwater at 0°C B. Freshwater at 25°C C. Freshwater at 100°C

Question 1

Which medium would transfer sound waves the slowest?

A. Freshwater at 0°C B. Freshwater at 25°C C. Freshwater at 100°C

Doppler Effect

The Doppler effect is produced by a sound source that is in motion.

When a siren is approaching it has a higher sound, but as it passes, its pitch suddenly drops to a lower sound

Doppler Effect

As the object approaches, it releases waves that are catching up to the waves it released earlier.

Thus, its pitch as an increased frequency and higher pitch.

Doppler Effect

As the object approaches, it releases waves that are catching up to the waves it released earlier.

Thus, its pitch as an increased frequency and higher pitch.

Breaking the Sound Barrier: Sonic Boom

As the plane exceeds the sound barrier, it also exceeds the doppler lines.

This results in a sonic boom. But, the pilot hears nothing since they are outrunning their own sound!

Question 2

 A fire truck is approaching you with its siren blaring. What would you notice about the sound of the siren?

A. There is no change in the intensity. B. There is no change in the frequency. C. The frequency seems to decrease. D. The frequency seems to increase.

Question 2

 A fire truck is approaching you with its siren blaring. What would you notice about the sound of the siren?

A. There is no change in the intensity. B. There is no change in the frequency. C. The frequency seems to decrease. D. The frequency seems to increase.

Advances in Sound Recording