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Harmonic Motion. Circular motion can be described by components. x = r cos q y = r sin q For uniform circular motion the angle is related to the angular velocity. q = w t. The motion can be described as a function of time. x = r cos w t y = r sin w t. Vector Components.
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Circular motion can be described by components. x = r cos q y = r sin q For uniform circular motion the angle is related to the angular velocity. q = wt The motion can be described as a function of time. x = r cos wt y = r sin wt Vector Components r r sin q q r cos q
Velocity Components • The velocity vector can also be described by components. • vx = -v sin q • vy = v cos q • This is the derivative of the position. v v cos q q -v sin q q
Acceleration Components • For uniform circular motion the acceleration vector points inward. • ax = -a cos q • ay = -a sin q • This is the derivative of the velocity. -a cos q q a -a sin q q
1 period Changing Angle to Position • If only one component is viewed the motion is sinusoidal in time. • This is called harmonic motion. • Springs and pendulums also have harmonic motion. x = A cos wt
Acceleration and Position • In uniform circular motion acceleration is opposite to the position from the center . • In harmonic motion the acceleration is also opposite to the position. This is true for all small oscillations
From the law of action the force is proportional to the acceleration. Harmonic motion has a position-dependent force. Force is negative Restoring force Spring Oscilations
Springboard • A diving board oscillates with a frequency of 5.0 cycles per second with a person of mass 70. kg. What is the spring constant of the board? • Find the spring constant from the mass and frequency. • With values: • k = 42(5.0 /s)2(70. kg) • K = 6.9 x 104 N/m next