PHY138 – Waves, Lecture 2Today’s overview

Hooke’s Law and Oscillation of Springs Hanging Springs The Pendulum Damped Oscillations; Shock Absorbers Driven Oscillations; Resonance

Want to do Want to do Research?Research?

For more info, visit: www.utoronto.ca/premed, or our Facebook group: U of T Pre-Medical Society

Pre-Med Society Annual Research Fair

Friday, Nov.9th @ 3:30MSB 3153

Learn about research opportunities from representatives of various Learn about research opportunities from representatives of various fields of science, as well as organizations at U of Tfields of science, as well as organizations at U of T

——LMP, physiology, immunology, and more!LMP, physiology, immunology, and more!

Pizza and drinks will be served! Pizza and drinks will be served!

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 isA. larger than before.B. the same as before.C. less than before.

Clicker QuizGravitational Potential Energy increases with height. Elastic Potential Energy increases as a spring is stretched. Kinetic Energy increases with speed.

Reading Assignment Next week’s 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 11:59PM.

Test 1 will be given back to you at the end of tutorial this week. Marks will be posted on STORM by Wednesday.

Two pendula have the same length, but different mass. The force of gravity, F=mg, is larger for the larger mass. Which will have the longer period?

A. the larger mass

B. the smaller mass

C. neither

Mass on Spring versus Pendulum Mass on a

SpringPendulum

Condition for S.H.M.

Small oscillations

(spring obeys Hooke’s Law)

Small angles

(sinθ ≈ θ)

Natural frequency [rad/s]

Period

L

g

m

k

k

mT 2

g

LT 2

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

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

14.7 Damped Oscillations

14.8 Externally Driven Oscillations

Resonance!