Transcript Lesson: Circular Motion

Do Now
• Which of the following objects is
accelerating:
a. A car slowing down.
b. A free fall object momentarily stopped at its
max height.
c. A ball tied to a string, being swung around in
circles at a constant speed.
Uniform Circular Motion
• An object which is moving in a circular path with
a constant speed is said to be in uniform
circular motion.
• Distance of a circle = circumference
d = 2πr
• (T) Period – time it takes an object to complete one
revolution.
time
T
# ofREV
d
v
t
2r
v
T
Kinematics of Uniform Circular Motion
Centripetal Acceleration (ac ): acceleration due to change in
direction rather than magnitude of the velocity, always point
towards center of the circular path.
v
a
r
2
v
a
r
Circular Motion: Gravitation
• The velocity vector is tangent to the path
of the ball, and points in the direction the
ball would move if the string were to break
at that instant.
A
B
C
21. A jet airplane is flying in a horizontal circle of radius 500 meters,
such that the jet will complete a full circular motion in a time of 25
seconds. What Velocity will the jet experience? (round to 1 decimal)
21. A jet airplane is flying in a horizontal circle of radius 500 meters,
such that the jet will complete a full circular motion in a time of 25
seconds. What Centripetal Acceleration will the jet experience?
(round to 1 decimal)
Centripetal Force (FC)
• Anytime an object accelerates centripetally
there must be a net force (ΣF) causing ac
• ΣFC must point towards the center
• ΣFC can represent
– FTension for a ball or a string
– Fg for orbit
– Ffric for car around a circular turn
Centripetal Force
 v2 
F  ma  m 
 r 
 v2 
F  m 
 r 
A clump of dried clay of mass .1 kg sits at the edge of a potter’s wheel
of radius 15cm. If the clump slips off when the wheel’s rotation rate
reaches 75 rpm (revolutions per minute)
a) determine the velocity of the clay (round to 1 decimal).
A clump of dried clay of mass .1 kg sits at the edge of a potter’s wheel
of radius 15cm. If the clump slips off when the wheel’s rotation rate
reaches 75 rpm (revolutions per minute)
b.) Determine the Centripetal Force (round to 2 decimals)
A clump of dried clay of mass .1 kg sits at the edge of a potter’s wheel
of radius 15cm. If the clump slips off when the wheel’s rotation rate
reaches 75 rpm (revolutions per minute)
c.) Calculate the coefficient of static friction between the clay and the
wheel. (used g = 9.8, round to 2 decimals)