Waves • Objectives • 1. Define vibration, oscillation, wave, medium, period, frequency, wavespeed, compression, rarefaction, interference, node, anti-node • 2. Explain how waves are formed • 3. Identify the parts of a wave • 4. Calculate period, frequency, and wavespeed • 5. Explain the factors that control wavespeed • 6. Describe the types of waves, interference, and a standing wave Definitions • vibration - any motion that repeats itself • oscillation - one complete motion of a vibrating object • wave - movement of energy without movement of matter - result of a vibrating object disturbing a medium • medium - the stuff through which a wave moves Parts of a Wave • nodal line - resting position of the medium • crest - high point on a wave • trough - low point on a wave • amplitude - the distance from the nodal line to the top of a crest or the bottom of a trough • wavelength - distance between crests or troughs Definitions • period - the time to complete one oscillation (measured in seconds) • frequency • number of oscillations in a given time • measured in hertz (Hz) • 1 oscillation/second = 1 Hz • examples • AM radio is broadcast in kilohertz (kHz) or 1000 cycles/second • FM radio is broadcast in megahertz (MHz) or 1,000,000 cycles/second • Frequency and period are related. • The longer the period, the smaller the frequency. (visa versa) Equation Key f = 1 ÷ T f = frequency (in Hz) T = period (in seconds) Wavespeed • the speed at which a wave travels • with a single pulse can be calculated from distance divided by time • depends on the medium (higher density = faster speed) • Can be calculated with frequency and wavelength Equation Key υ = wavespeed (in m/s) υ = f λ f = frequency (in Hz) λ = wavelength (in m) Two Types of Waves 1. Transverse – particles of the medium move perpendicular to the direction of the energy 2. Longitudinal – particles of the medium move in the same direction as the energy Two Areas in a Longitudinal Waves A. compression • the part of the medium that is pushed together • Becomes a crest of a transverse wave B. rarefaction • the part of the medium that is pulled apart • Becomes a trough in a transverse wave. Incidents and Reflections • Incident Wave – original disturbance • Reflection • when a wave bounces off a fixed point (echo) • reflection is on opposite side of nodal line • reverberation – repeated reflection Interference • when two waves collide • Two Types of Interference 1. constructive - amplitude increases 2. destructive – amplitude decreases Standing Waves • when incident wave and reflection match perfectly • nodes • area of destructive interference • point of no motion • anti-node • areas of constructive interference • point of maximum motion .