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## PowerPoint Slideshow about ' How do waves move?' - hina

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### Sound Wave

How do waves move?

- Compare solid liquid & gas
- Solid faster than liquid faster than gas (needs medium)
- More dense – faster
- What about light?
- Fastest in vacuum (no medium)
- More dense - slower

Sounds that are too high in frequency for humans to hear are called ultrasound. Normally, these sounds are above 20,000 Hz.

Sounds that are too low in frequency for humans to hear are called infrasound. Normally, these sounds are below 20 Hz.

Doppler effect

- Apparent change in pitch of a sound caused by the motion of object making sound

Infrasound is sound with a frequency too low to be heard by the human ear. The study of such sound waves covers sounds beneath the lowest limits of human hearing (20 hertz). Many animals, including whales, elephants, rhinoceros, giraffes, okapi, and alligators, communicate using infrasound.Used in movies to give a feeling of unease; can vibrate your whole body

INTERFERENCE

When two or more waves come together, they “superimpose” or add together. The total amplitude is simply the sum (positive & negative!) of all the individual amplitudes. The extremes of what can happen are called constructive interference and destructive interference

What is this called?

Destructive interference

Standing Wave

waves generated when a series of wave pulses are sent through a medium and then reflected back upon themselves.

Nodes – distructive interference

Antinodes – constructive interference

Refraction

- Occurs as waves move from one medium into another or within a medium, like air, that varies in density or temperature

Problems

- v = d / t speed = distance / time The unit for speed (or velocity) (v) is meter/second.The unit for distance (d) is meter.The unit for time (t) is second. v = 331 m/sec + (0.6 m/s/C) Tspeed of sound in air = 331 m/sec + (0.6)(room temperature)The unit for speed (or velocity) (v) is meter / second.
- The unit for room temperature (T) is degrees Celsius.
- v = f
- speed = frequency times wavelength
- The unit for speed (or velocity) (v) is meter/second. The unit for frequency (f) is Hertz (Hz).
- The unit for wavelength () is the meter.

Calculate the speed of sound for the following temperatures.

- 0 C (cold day)
- 35 C (hot day)
- 100C

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