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PHY131H1F - Class 8
Today, finishing off Chapter 4:
•Circular Motion
•Rotation
Quiz time… – Angular Notation: it’s all
Greek to me!
θ is an angle, and the S.I. unit of angle is rad.
The time derivative of θ is ω.
What are the S.I. units of ω ?
A. m/s2
B. rad / s
C. N/m
D. rad
E. rad /s2
dt
d
Quiz time… – Angular Notation: it’s all
Greek to me!
The time derivative of ω is α.
What are the S.I. units of α ?
A. m/s2
B. rad / s
C. N/m
D. rad
E. rad /s2
d
dt
Last day I asked at the end of class:
•You are driving North Highway
427, on the smoothly curving part
that will join to the Westbound 401.
Your speedometer is constant at
115 km/hr. Your steering wheel is
not rotating, but it is turned to the
left to follow the curve of the
highway. Are you accelerating?
•ANSWER: YES! Any change in velocity, either
magnitude or speed, implies you are accelerating.
•If so, in what direction?
•ANSWER: West. If your speed is constant,
acceleration is always perpendicular to the velocity,
toward the centre of circular path.
v
a
Circular Motion r = constant
s and θ both
change as the
particle moves
s = “arc length”
θ = “angular
position”
when θ is measured in radians
Angular Velocity
when ω is measured in rad/s
