AIR Helmholtz Resonator Pressure 1 Pressure 2 Column

AIR Helmholtz Resonator Pressure 1 Pressure 2 • Column of air in neck of bottle moves up and down (oscillates) as you blow across it • Changes pressure inside the bottle cavity • Makes sound waves that move out from the bottle • Twice the volume, half the frequency (down one octave) • Longer neck, lower frequency

How to Blow Across a Bottle • Hold to lower lip vertically • Pull bottom lip tight • Make rectangle with mouth • Direct air horizontally across bottle top • Breath out!

Boomwackers and Singing Tubes • Hit Boomwackers to create standing pressure wave • Twirl Singing tube to create standing pressure wave • These pressure differences create sound waves that ripple out (propagate). • Boomwackers: Open tube will have frequency f, closed tube will have lower frequency of ½ f (down an octave) • Boomwackers: Twice as long of tube, frequency drops ½ (down an octave) • Singing Tubes: Spin faster, higher frequency Open Tubes One End Closed Diagrams depict air vibration Boomwackers and Singing Tubes

Tuning Forks in Water • Tuning forks make sound waves we can hear • If placed in water, these waves are visible – just like waves from dropping pebbles in water • Longer tuning forks give lower frequency waves

Sympathetic Vibrations • Sympathetic vibrations mean that sometimes, when one thing vibrates, another will start vibrating along with it • Need to be same (have same natural frequencies) • Small wires vibrate faster (high frequency) than long ones • Pluck the long wire and only other long wire will vibrate • Pluck small wire and only other small wire will vibrate Stationary corks on wires Plucked long wire

Transverse Waves in a Spring • Each person hold an end of the Slinkytm. • One person shake the end back and forth slow. • Try to get the Slinkytm to make this shape: • Now try to shake faster. • If you shake twice as fast, you get this shape: • Shake three times as fast, and you’ll get: • See how many bumps you can make. • Switch off so the person on the other end can shake too.

About Waves • There are two types: – Transverse • Like regular water waves. – Compression (Longitudinal) • Material is scrunched at parts and stretched at others. • Pulses: – Like a single wave moving in a direction. Pulse • Waves have different speeds – Sound waves travel faster in water than air. – Sound travels faster in Helium than air. • This can cause squeaky voices! – Sound can travel much faster in a solid. Scrunched Stretched

Attenuation and Channeling • Sound travels outwards in all directions, like a ball getting bigger. • Because of this, sound gets quieter the farther it travels. • Megaphones help direct the sound so more of it gets where you want it to go.

Attenuation and Channeling • We can make sound travel farther if we talk down a tube. The sound has no where to spread, so it sounds the same at both ends. (Talk quietly, it is like you are talking into their ear. ) • When sound meets a change in temperature, it can curve. One example is warmer air or water. This effect is called channeling.

Sound Propagation http: //www. resonancepub. com/unwateracou. htm

• Column of air in neck of bottle moves up and down as you blow across it • Changes pressure inside the bottle cavity • Makes sound waves