Sound Demonstrations

Cool Tricks!

http://www.youtube.com/watch?v=Ude8pPjawKI

Sound Waves – The Basics

• Produced by vibration• Carry energy through a medium, which means

they are mechanical waves

Humans hear sounds waves in a limited frequency range

• From 20 vibrations per second (20 Hertz) to 20,000 vibrations per second (20,000 Hertz)

• The number of vibrations that are produced per second is called frequency.

• Frequency varies for each sound and is measured in hertz. One hertz is equal to one vibration per second.

How will your hearing range change?

• The hearing range of humans gets worse with age. People lose the ability to hear sounds of high frequency as they get older.

• The highest frequency that a normal middle-aged adult can hear is only 12-14 kilohertz.

• Also, the hearing range for men worsens more quickly than the hearing range for women.

• This means that women will have the ability to hear notes of higher pitch than men of the same age do.

Earbuds and Hearing Loss

http://abcnews.go.com/WNT/video/earbuds-lead-hearing-loss-18679650

How does frequency affect pitch?

• A sound with a low frequency will have a low pitch, such as a human's heartbeat.

• A sound with a high frequency will have a high pitch, such as a dog whistle.

• Sound below the range of human hearing is Infrasound.

• Sound with a frequency above the range of human hearing is Ultrasound.

Pitch – a measure of how high or low a sound is, depends on frequency

• Ex: Slide Whistle, Boom Whackers

• How does wavelength affect pitch?

Mechanical waves need a medium!

• Clock in a vacuum - http://www.youtube.com/watch?v=ce7AMJdq0Gw

Medium affects the speed of the wave!• Example: Oven racks (vibrations, pitch and

frequency)

Speed of sound

• In Air (0 degrees C) = 331 m/s• In Air (100 degrees C) = 386 m/s• Oxygen = (0 degrees C) = 317 m/s• In Water = 1,490 m/s• Copper = 3,813 m/s• Rubber = 54 m/s

Standing Wave

• Guitar or Violin String

• Pressing down on the string creates a node at that point.

• The location of the node determines the pitch of the note.

Interference• When several waves are in

the same location, they combine to produce a single, new wave that is different from the original wave.

• Constructive Interference increases the amplitude.

• Destructive interference decreases amplitude.

Bottles and Tuning Fork• Each time the tuning fork is held above the glass bottles you are actually

hearing 2 sounds, not one.

• You are hearing the sound made by the tuning fork and the sound that reflects off the water and reemerges from the jar.

• When the reflected wave reemerges, it overlaps with the wave coming from the tuning fork.

• If the wave emerging from the jar overlaps constructively you will hear a loud sound.

• If the emerging wave overlaps destructively, you will hear no sound or a very low amplitude sound.

• How does this demo also relate to Resonance?

Doppler Effect• Motion between the source of

waves and the observer creates a change in observed frequency.

• Frequency changes the Pitch• Examples

– Ambulance– Doppler ball– Doppler Radar – Radar dome

receives radio waves that have been sent out an then reflected back by rain, snow, and hail. Meterorologist observe frequency shifts.

Do you remember learning about the Doppler Shift (red shift) in space science?