Chapter 13 Waves and Sound Vibrations Waves Wave

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.

Mathematical term for a wave is a: sine curve (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

• Frequency (Hertz) or (Hz): 1 vibration per second is 1 Hz; 5 vibrations per second = 5 Hz • Period – the time it takes for a complete vibration 1 Frequency = ----period 1 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=fλ V = wave speed f = frequency λ = wavelength

Open-Notebook Quiz 1. 2. 3. 4. 5. 6. 7. 8. The mathematical term for a wave is a ______. T/F Sound can travel through a vacuum. T/F Light does not need materials in order to exist. ______ 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.