An Introduction to Waves
⚠ Students sensitive to flashing lights are to avoid certain strobe light demonstrations!
⚠ 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
Frequency & Pitch
Amplitude & Loudness
Transverse and Longitudinal Waves
Peak / Crest and Valley / Trough
Rarefaction and Compression
Standing Waves, Nodes, & Anti-nodes
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
Parts of a 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?
- 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
When longitudinal waves run into each other, they briefly change each other's amplitude or how loud they are
Interference of Transverse
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