# Ch 15 Oscillation Simple Harmonic Motion 15 2

• Slides: 19

Ch 15 Oscillation • Simple Harmonic Motion (§ 15 -2~ § 15 -4) – phase & phase constant – angular frequency ω – velocity & acceleration of SHM – Force law for SHM (§ 15 -3) – Energy in SHM (§ 15 -4) • 微分方程式和它的解 – 單擺、複擺、扭擺 • Springs & Pendulums (§ 15 -6, § 15 -5) – 水平彈簧、垂直彈簧 • 等效擺與振盪中心 • Simple Harmonic Motion and Uniform Circular Motion(§ 15 -7) • Damped , Forced Oscillations and Resonance (§ 15 -8, § 15 -9)

Mr. Hooke ut tensio sic vis 彈性與力成正比（1678年） 秤上刻字： 虎克發明於 1658年 湯平製作於 1675年 Galilei(1564~1642) Huygens(1629~1695) Hooke(1635~1703) Newton(1642~1727)

Ch 15, Problem 88 (Vertical Spring) A 50. 0 g mass is attached to the bottom of a vertical spring and set vibrating. If the maximum speed of the mass is 15. 0 cm/s and the period is 0. 500 s, find (a) the constant of the spring, (b) the amplitude of the motion, and (c) the frequency of oscillation. (d)平衡時，伸長量 x 0 =？ Homework：Problem 81, 89

Sample Problem 15 -5 這二個擺有什麼共同性？ P 點的意義？ The center of oscillation

Ch 15, Problem 110 Baseball： sweet spot 1/2 The center of oscillation of a physical pendulum has this interesting property: if an impulsive force (assumed horizontal and in the plane of oscillation) acts at the center of oscillation, no reaction is felt at the point of support. Baseball players (and players of many other sports) know that unless the ball hits the bat at this point (called the “sweet spot” by athletes), the reaction due to the impact will sting their hands. To prove this property, let the sick in Fig. 15 -11 a simulate a baseball bat.

Ch 15, Problem 110 Baseball： sweet spot 2/2 Suppose that a horizontal force F (due to impact with the ball) acts toward the right at P, the center of oscillation. The batter is assumed to hold the bat at O, the point of support of the stick. F (a) What acceleration does point O undergo as a result of F ? (b) What angular acceleration is produced by F about the center of mass of the stick? (c) As a result of the angular acceleration in (b), what linear acceleration does point O undergo? (d) Considering the magnitudes and directions of the accelerations in (a) and (c), convince yourself that P is indeed the “sweet spot”.

§ 15 -7 SHM & Uniform Circular Motion • 1610 • Galileo • telescope • four principal moons of Jupiter

§ 15 -8 阻尼振盪 damped oscillator

§ 15 -9 Forced Oscillations & Resonance ω：natural angular frequency ωd：angular frequency of the external driving force 驅動力

Damped Oscillations Forced Oscillations 微分方程式 (15 -45) (15 -42) (Problem 62) 位移振幅 咦. (15 -45)為什麼沒有類似 這一項? 振幅隨著時間增加而衰減

Forced Oscillations