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Simple Harmonic Motion (SHM). (and waves). What do you think Simple Harmonic Motion (SHM) is???. Defining SHM. Equilibrium position Restoring force Proportional to displacement Period of Motion Motion is back & forth over same path. Θ. F g. Describing SHM. Amplitude. Θ. F g.
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Simple Harmonic Motion (SHM) (and waves)
Defining SHM • Equilibrium position • Restoring force • Proportional to displacement • Period of Motion • Motion is back & forth over same path
Θ Fg Describing SHM • Amplitude
Θ Fg Describing SHM • Period (T) • Full swing • Return to original position
Frequency • Frequency- Number of times a SHM cycles in one second (Hertz = cycles/sec) • f = 1/T
SHM Descriptors • Amplitude (A) • Distance from start (0) • Period (T) • Time for complete swing or oscillation • Frequency (f) • # of oscillations per second
Oscillations • SHM is exhibited by simple harmonic oscillators (SHO) • Examples?
Examples of SHOs • Mass hanging from spring, mass driven by spring, pendulum
SHM for a Pendulum • T = period of motion (seconds) • L = length of pendulum • g = 9.8 m/s2
EPE = ½ k x2 • KE = ½ m v2 • E = ½ m v2 + ½ k x2 • E = ½ m (0)2 + ½ k A2E = ½ k A2 • E = ½ m vo2 + ½ k (0)2E = ½ m vo2
√ Velocity • E = ½ m v2 + ½ k x2 • ½ m v2 + ½ k x2 = ½ k A2 • v2 = (k / m)(A2 - x2) = (k / m) A2 (1 - x2 / A2) • ½ m vo2 = ½ k A2 • vo2 = (k / m) A2 • v2 = vo2 (1 - x2 / A2) • v = vo 1 - x2 / A2
Damped Harmonic Motion • due to air resistance and internal friction • energy is not lost but converted into thermal energy
Damping • A: overdamped • B: critically damped • C: underdamped
Resonance • occurs when the frequency of an applied force approaches the natural frequency of an object and the damping is small (A) • results in a dramatic increase in amplitude