Waves Chapter 11 Section 1

What is a wave? A wave is a repeating disturbance or movement that transfers energy through matter or space Waves transfer energy NOT matter Medium: the matter through which a wave travels; i.e. water, air

Motion of a Duck on a Wave

Water Wave

Mechanical Waves Waves that can travel only through matter There are two types: Transverse waves (water, and some seismic waves) Longitudinal waves (sound, spring) Requires a medium!!!!!!!

Longitudinal (compressional) Waves Particles in the medium move parallel to the direction of the waves.   particle motion     wave motion   The dense areas are called compressions. The less dense areas are rarefactions.

Transverse Waves Particles in the medium move perpendicular to the direction of the waves. wave motion particlemotion

Parts of a Wave Crest: the highest point (top) of a transverse wave. Trough: the lowest point (bottom) of a transverse wave. Wavelength: the distance from any point on a wave to the same point on the next wave. (ex: crest to crest) Amplitude: the height measured from the resting position.

Parts of a Wave crest wavelength amplitude trough

Seismic Waves Seismic waves are a combination of compressional and transverse waves 1. They can travel along the earth’s surface 2. When objects on the Earth’s surface absorb some of the energy carried by seismic waves, they move and shake Compressional Transverse

Greater amplitude = more energy. Measures the amount of energy in a wave. Greater amplitude = more energy.

FREQUENCY The rate at which waves pass (the # of full wavelengths that pass a point in one second). Symbol: f Unit: Hertz (Hz) 1 Hertz = 1 vibration per second Frequency is 1 / T

WAVE SPEED How fast a wave moves. Symbol: v Unit: m/s Wave speed is determined by the medium. Generally, waves pass through solids faster b/c particles are closer and can pass vibrations to each other more quickly.

EQUATIONS v = f · λ f = v / λ λ = v / f v UNITS: λ = meters (m) Wave speed = frequency times wavelength v = f · λ f = v / λ λ = v / f UNITS: λ = meters (m) f = Hertz (Hz) v = m/s v f λ

The string of a piano that produces the note middle C vibrates with a frequency of 264 Hz. If the sound waves produces have a wavelength of 1.30 m in air, what is the speed of sound in air? f = 264 Hz λ = 1.30 m v = ? v = 264 Hz (1.30 m) v = f · λ v = 343.2 m/s

A water wave has a speed of 1. 3 m/s A water wave has a speed of 1.3 m/s. A person sitting on a pier observes that it takes 1.2 s for a full wavelength to pass the edge of the pier. What is the wavelength of the water wave? v = 1.3 m/s T = 1.2 s f = 1 / T = 1 / 1.2 s = 0.83 Hz λ = ? λ = 1.3 m/s / 0.83 Hz λ = v / f λ = 1.57 m