Thought for the Day

1
Thought for the Day
2
Midterm

• Friday October 26, 57pm
• room to be determined
• one person writing early (must email me today)

3
Tutorials/TAs

• Tutorials
• T0101 M 10am, MP 134
• T0201 T 10 am, MP 137
• Teaching Assistant
• Jean-Sébastien Bernier

4
Study groups

• if youd like help to find others wanting to form
  study groups, send me an email LIKE THIS
• Subject ABC PHY255 study
• no content in the body
• Ill send out an email to those people, with all
  peoples addresses in the To field (in the clear)

5
Modelling oscillations
6
Elements of an oscillator

• need inertia, or its equivalent
• mass, for linear motion
• moment of inertia, for rotational motion
• inductance, e.g., for electrical circuit
• need a displacement, or its equivalent
• amplitude (position, voltage, pressure, etc.)
• need a negative feedback to counter inertia
• displacement-dependent restoring force spring,
  gravity, etc.
• electrical potential restoring charges

7
Hookes Law

• restoring force proportional to displacement from
  equilibrium

8
Oscillation of mass on spring
restoring force
inertial force
equation of motion

• x(t) is a function describing the oscillation
• what function gives itself back after twice
  differentiated, with negative constant?
• cos(at), sin(at) both do work
• exp(at) looks like it ought to work...

9
Oscillation of mass on spring
try

• frequency determined by spring constant k, and by
  mass m.
• cos(wtfo) is similar

10
Phasor notation
try

• x(t)Aexp(iwtfo) is a solution also