Chapter 13 Waves and Sound

Vibrations & Waves Wave: A vibration that moves through space and time. Sound – the movement of vibrations of matter – through solids, liquid or gases - if there is no matter to vibrate, then there is no sound. Sound cannot travel through a vacuum. Light – Vibration of electric & magnetic fields – vibration of pure energy. Light can travel through materials, but none is required.

sine curve Mathematical term for a wave is a: (shaped like rolling hills and valleys)

Crests = high points of wave Troughs = low points of wave Midpoint or “home” position

Amplitude – distance from midpoint to crest or trough of the wave Wavelength – distance from one crest to the next one Frequency – how often a wave occurs

Period = -------------- Frequency (Hertz) or (Hz): 1 vibration per second is 1 Hz; 5 vibrations per second = 5Hz Period – the time it takes for a complete vibration 1 Frequency = --------- period Period = -------------- frequency

Wave Speed Energy is carried by waves not the material it’s moving through – speech and air Example: when you talk the energy of your voice travels across the room at ~340 meters/second. Wave energy travels, not the air itself.

Wave Speed = frequency X wavelength Example: If a water wave vibrates up and down three times each second and the distance between wave crests is 2 m, what are (a) the wave’s frequency? (b) its wavelength? (c) its wave speed? (a) 3 Hz; (b) 2 m; (c) 6 m/s

Wave Speed v = f λ V = wave speed f = frequency λ = wavelength

Open-Notebook Quiz 1. The mathematical term for a wave is a ______ ______. 2. T/F Sound can travel through a vacuum. 3. T/F Light does not need materials in order to exist. 4. ______ are the high points in a wave. ______ are the low points in the wave and the _______ position is the mid-point of a wave. _______ tells you the distance from the mid-point of a wave to its trough or crest. ________ is the distance from one crest to the next one. T/F Frequency tells you how often a wave occurs and is measured in Hertz (Hz). What is the formula for figuring out the period of a wave, which is the time it takes for a complete vibration.