Vibrations and Waves

Wave: A Disturbance That Travels

Or…

A Wiggle in Space

Wavelength (λ) = Distance from one crest to the next crest.Measured in meters.

Frequency (f) = Number of vibrations every second.Measured in Hertz (cycles/second).

Amplitude = Distance from the midline to the crest.Measured in meters.

Period = Time needed to make one vibration.

wavelengthfrequency Waveof Speed

Slinky

Who walks the stairs without a care It shoots so high in the sky.

Bounce up and down just like a clown. Everyone knows its Slinky.

The best present yet to give or get. The kids will all want to try. The hit of the day when you are ready to play. Everyone knows it's Slinky.

It’s Slinky, It’s Slinky for fun the best of the toys. It’s Slinky, It’s Slinky the favorite of girls and boys.

Slinky: A spring that is very flexible, lots of mass

Transverse Waves

Vibration is perpendicular to the direction of the wave.

Longitudinal Waves

Vibration is parallel to the direction of the wave.

Sound

Sound: Vibration of a material substance that has a frequency the human ear can pick up.

Sounds are longitudinal waves.

There are no sounds in space!

Compression: The air (or other material) is compressed.

High pressure.

Rarefaction: The air (or other material) is spread out.

Low pressure.

Not Just Air!

Many media can produce sound waves. Must possess “elasticity.”

Elasticity: The ability to distort and then “rebound” back to normal.

Water and Steel are examples of elastic substances that can transmit sound.

Waves Generated by Earthquakes

P-waves: Longitudinal. S-waves: Transverse.

Reflection of Sound

The reflection of sound is called an echo.

Anechoic Chamber: A room designedto eliminate reflections.

Refraction of Sound Waves

Sound waves can bend (refract)

The warmer the air, the faster sound travels.

At room temperature, speed travels at about 344 m/s.

Forced Vibrations

One vibrating objectforces another to

vibrate.

Acoustic string Instruments.

Resonance

A forced vibration that matches an

objectsnatural frequency.

Tacoma Narrows Bridge

Interference

Multiple waves add and subtract from each other.

Examples of Interference

Standing Waves

Nodes and Antinodes

½ λ

1 λ

1½ λ

Doppler Effect

If the source of a wave is moving towards or away from you, the frequency changes.

Bow Waves and Shock Waves

Creation of Bow Waves

MUSIC

Noise is random, music is organized

Instruments differ in the type and mixture ofharmonics.

Energy in Sound Waves

Energy of 10,000,000 people talking at once would barely power a common flashlight.

Sound energy is stored in the compression (potential energy) and released in the rarefaction (kinetic energy).