11-5 Damped Harmonic Motion Typically, harmonic motion decreases in amplitude with time….this realistic model describes damped harmonic motion. The damping effect is a result of friction and internal resistance of the system to further motion. Overdamped means damping is so great that equilibrium takes longer to achieve. Underdamped means that a lack of damping causes the system to oscillate more freely and for longer… Critical damping means the system is damped to achieve equilibrium the quickest way.
11-6 Forced Vibrations: Resonance • Natural frequency is the frequency that a system vibrates without interference… • A forced vibration would be a vibration caused by an external force acting on a system. When damping is small, the amplitude is greatest at f=f0 …this is called resonance. • Natural frequency is also called resonant frequency.
11-7 Wave Motion • Mechanical waves are waves that involve particles or media moving in wave-like fashion… usually easy to see or touch. • Waves move at different velocities than the particles of the media in which they travel. • See 11-9 p323 • A pulse is a single wave that travels through a medium. • Wavelength is the distance between identical points in 2 successive waves.
Wave Motion (cont’d) • A continuous or periodic wave has repeating pulses in a consistent pattern. • Amplitude = ½ height
Wave Motion (cont’d) • Wave velocity = n=lf (n=c for light waves) • See example 11-10 P326
11-8 Types of Waves • A transverse wave is one in which the medium or particles are moving perpandicular to the direction of the wave propagation. • A longitudinal wave is one in which the medium or particles are moving in the same direction as wave propagation.
Waves (cont’d) • A wave traveling down a solid rod … • …where E is the elastic modulus… • …where B is the bulk modulus for a gas or liquid. • See Example11-11 page 328
Homework (…keep your hands off of the key board!!!) • Page 342 pr# 17, 28-30, 34-40 due BOP Thursday