PHY138

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PHY138 Waves, Lecture 2Todays overview

• Hookes Law and Oscillation of Springs
• Hanging Springs
• The Pendulum
• Damped Oscillations Shock Absorbers
• Driven Oscillations Resonance

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Pre-Med Society Annual Research Fair Friday,
Nov.9th _at_ 330 MSB 3153
Learn about research opportunities from
representatives of various fields of science, as
well as organizations at U of T LMP, physiology,
immunology, and more!
For more info, visit www.utoronto.ca/premed, or
our Facebook group U of T Pre-Medical Society
Pizza and drinks will be served!
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Clicker Quiz
Gravitational Potential Energy increases with
height. Elastic Potential Energy increases as a
spring is stretched. Kinetic Energy increases
with speed.
A mass hangs motionless from a spring. When the
mass is pulled down and held at rest, the total
energy of the mass and spring is A. larger than
before. B. the same as before. C. less than
before.
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Reading Assignment

• Next weeks reading is Knight Chapter 20,
  Sections 20.1 20.7. (We are skipping Chapters
  15,16,17,18 and 19.) There is a pre-class quiz on
  www.masteringphysics.com for Chapter 20 due on
  Monday morning.
• A www.masteringphysics.com Problem Set on Chapter
  14 is due on Friday at 1159PM.
• Test 1 will be given back to you at the end of
  tutorial this week. Marks will be posted on
  STORM by Wednesday.

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• Two pendula have the same length, but different
  mass. The force of gravity, Fmg, is larger for
  the larger mass. Which will have the longer
  period?
• A. the larger mass
• B. the smaller mass
• C. neither

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Mass on Spring versus Pendulum
Mass on a Spring Pendulum
Condition for S.H.M. Small oscillations (spring obeys Hookes Law) Small angles (sin? ?)
Natural frequency rad/s
Period
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• A person swings on a swing. When the person sits
  still, the swing oscillates back and forth at its
  natural frequency. If, instead, two people sit
  on the swing, the natural frequency of the swing
  is
• A. greater
• B. the same
• C. smaller

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• 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

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14.7 Damped Oscillations
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14.8 Externally Driven Oscillations
Resonance!