a) period will increase b) period will not change c) period will decrease

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1 Physics 101 Tuesday 11/3/11 Class 21" Chapter " Period of a mass on a spring" Energy conservation in oscillations" Pendulum" Damped oscillations" " A glider with a spring attached to each end oscillates with a certain period. If the mass of the glider is doubled, what will happen to the period? a) period will increase b) period will not change c) period will decrease A mass oscillates on a vertical spring with period T. If the whole setup is taken to the Moon, how does the period change? a) period will increase b) period will not change c) period will decrease Period of springs! A mass on a spring oscillates with a certain amplitude and a certain period T. If the mass is doubled, the spring constant of the spring is doubled, and the amplitude of motion is doubled, the period.. A: increases B: decreases C: stays the same. 1

2 A mass oscillates in simple harmonic motion with amplitude A. If the mass is doubled, but the amplitude is not changed, what will happen to the total energy of the system? a) total energy will increase b) total energy will not change c) total energy will decrease If the amplitude of a simple harmonic oscillator is doubled, which of the following quantities will change the most? a) frequency b) period c) maimum speed d) maimum acceleration e) total mechanical energy Worked eample, problem 13.55! A 3 g bullet embeds itself in a 1.5 kg block, which is attached to a spring of force constant 750 N/m. IF the maimum compression of the spring is 6.0 cm, find A) the initial speed of the bullet B) the time for the bullet block system to come to rest (the first time). Two pendulums have the same length, but different masses attached to the string. How do their periods compare? a) period is greater for the greater mass b) period is the same for both cases c) period is greater for the smaller mass 2

3 Two pendulums have different lengths: one has length L and the other has length 4L. How do their periods compare? a) period of 4L is four times that of L b) period of 4L is two times that of L c) period of 4L is the same as that of L d) period of 4L is one-half that of L e) period of 4L is one-quarter that of L A swinging pendulum has period T on Earth. If the same pendulum were moved to the Moon, how does the new period compare to the old period? a) period increases b) period does not change c) period decreases A grandfather clock has a weight at the bottom of the pendulum that can be moved up or down. If the clock is running slow, what should you do to adjust the time properly? a) move the weight up b) move the weight down c) moving the weight will not matter d) call the repairman Pendulums! A person swings on a swing. When the person sits still, the swing oscillates back and forth at its natural frequency. If, instead, the person stands on the swing, the natural frequency of the swing is.. A: greater. B: the same. C: smaller. Eric Mazur, "Peer Instruction"

4 Pendulums! Physical Pendulums! I The period of a physical pendulum is T = 2!. mgl Compare the periods of two physical pendula. One is a solid disk of mass m, radius R, supported at the edge. The Disk Hoop other is a hoop also of mass m, radius R, supported at the edge. (I disk < I hoop ) Which has the longer period? A: Disk B: Hoop C: The periods are the same. Physical pendulums! I The period of a physical pendulum is T = 2!. mgl Compare the periods of two physical pendula. One is a solid disk of mass m, radius R, supported at the edge. The Physical pendulums! I The period of a physical pendulum is T = 2!. mgl Compare the periods of two physical pendula. One is a solid disk of mass m, radius R, supported at the edge. The Disk Hoop other is a hoop also of mass m, radius R, supported at the edge. On the moon, is the period different than on the Earth? A: longer on Moon B: shorter C: The periods are the same. Disk Hoop other is a hoop also of mass m, radius R, supported at the edge. What happens to the period T of the hoop physical pendulum, when the mass is doubled? (Careful! What happens to I?) A: T new = T old B: T new = (T old )/2 C: T T new = old / 2 4

5 Energy! A stiff spring and a floppy spring have potential energy diagrams shown below. Which is the stiff spring? Energy! A B A B Two masses are identical. One is attached to a stiff spring(spring B) ; the other to a floppy spring (Spring A). Both are positioned at =0 and given the same initial speeds. Which spring produced the largest amplitude motion? A: The floppy spring B: The stiff spring Damped oscillations! Forced Oscillations! Is A a case of A) Over damped B) Critically damped C) Underdamped..oscillation?! The best way to add energy to an oscillator (such as a pendulum) is to push it A) with the same frequency as it is swinging B) with twice the frequency it is swinging C) At half the frequency it is swinging 5

6 Forced Oscillations! This shows the amplitude resulting from the same driving force applied at different frequencies relative to the natural frequency of the oscillator. Forced Oscillations! Show Tacoma Narrows bridge (no physics class complete without it but eplain that it doesn t really show what the book says. Reading Assignment! Conservation of mechanical work! Problem Demos springs, pendulum Tuesday 11/ , Thursday 11/

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