Waves Waves A wave is a rhythmic disturbance
Waves
Waves • A wave is a rhythmic disturbance that carries energy through matter or space. • Examples of Waves: Light Radio waves Sound Electric signals Ocean waves Earthquakes Vibrations in structures (musical instruments)
Waves • All waves have a source and travel through a medium The source is the thing that is causing the wave The medium is what the wave travels through
Waves • Mechanical waves require a medium made of matter. • Air (sound waves) • Water (sound waves, sonar) • Rock (earthquake) • Interface between water and air (ocean waves) • There are three types of mechanical waves: • longitudinal • transverse • surface
Waves • Longitudinal waves • A longitudinal wave is a wave that vibrates parallel to the direction of the wave motion • Example: sound waves
Waves • Transverse waves • A transverse wave is a wave that vibrates perpendicular to the direction of wave motion. • Example: waves on a rope or string
Waves • Surface waves exist at the interface of two media (e. g. , water and air ocean waves) • They exhibit characteristics of both longitudinal and transverse waves. • Examples: ocean waves, surface-traveling earthquake waves
Waves • Pulse vs. periodic waves • Speed and amplitude apply to both types • Period, frequency, wavelength apply only to periodic waves
Waves • Anatomy of a periodic wave:
Waves • Speed • Depends only on the medium • Measured by tracking a pulse (v = x/ t) • Amplitude • Is how “big” the wave is • Depends on how the wave is generated • Is proportional to the wave’s energy
Waves • Wavelength • Shortest distance between crests (or troughs) • Represented by the Greek letter lambda, • Period • Like the period of a simple harmonic oscillator • The time it takes the wave to repeat itself (one complete cycle) • Represented by the letter T
Waves • Frequency • Is the number of complete oscillations a wave makes each second • Represented by the letter f • Frequency and period are related by the equation: f = 1/T • Frequency and period depend only on the source of the wave
Waves wavelength, , depends on both period (or frequency) and speed • Therefore, wavelength depends on both the source and the medium • = v. T = v/f • Wave speed equation: v = f
Example Calculation • The crest of a periodic ocean wave passes the same point once every 17 s. Find the speed of the wave if the wavelength is 130 m. T = 17 s = 130 m v = f = /T = (130 m)/(17 s) = 7. 6 m/s
- Slides: 17