# Sound

An Introduction to Waves

Reference - Forumla Sheet

## ⚠ Students sensitive to flashing lights are to avoid certain strobe light demonstrations!

Activities

⚠ Strobe Light & Tuning Fork Lab - Watch how the tuning fork behaves when struck and held under a strobe. Keep changing the strobe frequency to see what else happens!

⚠ Strobe Light & String Thing Demo - A spinning string makes the standing wave more visible under a strobe

Whirly Tube Demo - Listen and watch as we spin the whirly tube slowly, then faster, and faster

Singing Rods - Get annoyed as Mr. Ho gleefully plays some of the worst sounds you've ever heard

Sound Has a Length Lab - Extrapolate the speed of sound from measurements and calculations

Whoosh Ball demo - Listen for the Doppler effect as a buzzer embedded into a ball passes by

Topics

Frequency & Pitch

Wavelength

Amplitude & Loudness

Transverse and Longitudinal Waves

Peak / Crest and Valley / Trough

Rarefaction and Compression

Standing Waves, Nodes, & Anti-nodes

Resonance

Doppler Effect

Shock Wave & Sonic Boom

Wave Interference & Beats

## Students are Expected to Understand

How Manipulation of Longitudinal Wave Properties Can Affect a Sound

Wave Phenomena from Interactions and Behaviors Such as Interference, Beats, Shock Wave, Doppler Effect, Refraction, and Diffraction

*These videos are to be used as a supplement and are not a replacement for in-class experiences

# Transverse Wave

• You'll need to be familiar with the parts of a wave as we'll be talking about them a lot
• You get this sort of wave when you shake something up and down or left and right
• Wavelength can be represented with the symbol lambda λ
• "crest" can also be called peak
• "trough" can also be called valley
• How many wavelengths do you count in this wave? I see 2 wavelengths or 2 λ. Do you?

# Longitudinal Wave

• It would be useful to have these parts of this longitudinal wave memorized as well
• This kind of wave is made when you shake something forward and backwards or when you squeeze something and let go
• How many wavelengths do you count in this wave? I count 2 and a half wavelengths or 2.5 λ

## Longitudinal Wave Animation

Which direction is the wave moving? Now take a look at the red dots. How are they moving? How far do they go? Why aren't they moving to the right?

This is an example of a sound wave. Any time you speak, this is what your voice does to the air. Higher pitches have more waves or a higher frequency. When the wave reaches the ear, it pushes the ear drum back and forth vibrating it with a compression pushing the eardrum in and a rarefaction pulling it out, just a tiny bit but very fast. Humans can pick up vibrations as low as 20 times per second up to 20 thousand times per second or 20 Hz - 20 kHz

# Wave Interference

When longitudinal waves run into each other, they briefly change each other's amplitude or how loud they are

## and Longitudinal Waves

When waves meet each other, they can momentarily increase amplitude (constructive interference or in phase) or decrease amplitude (destructive interference or out of phase) as they pass through each other. Take a look at the second row. Notice that when a compression and rarefaction line up, the longitudinal wave gets stronger

## Transverse Wave Interference Animation

This really helps me understand how transverse waves meet and change each other temporarily. When the waves are really big, there's a large amplitude, and we call that constructive interference. And when the waves are little to no wave, we can call that destructive interference.

When are the waves biggest? When the crests and troughs of the two waves line up