Transcript Circular motion

AL Physics
Circular Motion
Circular motion
• Revision
• Circular motion in horizontal
• Vertical circular motion
• Loop-the-loop
Revision
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Newton’s Laws
Circular motion in horizontal circles
Centripetal force and acceleration
Angular velocity, frequency & linear
velocity
Newton’s first Law
A body continues in a state of
rest or uniform motion in a
straight line unless it is acted
upon by external forces.
Newton’s first Law
No external force
The body remains at rest.
The body moves with a constant speed.
Newton’s second Law
The rate of change of momentum
of a body is proportional to and
in the same direction as the
resultant force that acts on it.
d (mv)
Fnet 
 F  ma if m is constant
dt
Newton’s second Law
For fixed force
A body with a larger mass moves with a smaller acceleration .
A body with a smaller mass moves with a larger acceleration .
Newton’s second Law
For fixed mass
A body with a smaller net force moves with a smaller acceleration .
A body with a larger net force moves with a larger acceleration .
Newton’s third Law
If one body exerts a force on
another, there is an equal and
opposite force, called reaction,
exerted on the first body.
Newton’s third Law
Body A exerts a force on body B, then body B exerts an equal
and opposite force on body A.
Force on A by B
Body A
Force on B by A
Body B
Newton’s third Law
Circular Motion in horizontal circles
Circular Motion in horizontal circles
Centripetal force
F = m r 2 = m v2 / r
Centripetal acceleration
a = r 2 = v2 / r
Linear velocity
v =r
Angular velocity
=/t
Circular Motion in horizontal circles
Conical pendulum
Circular Motion in horizontal circles
Conical pendulum
Do you remember what kind of
forces provides the centripetal
force to the bob ?
Tension T
Centripetal force
Weight mg
Vertical circular motion
Bucket and water
Does the water spill out the
bucket when whirling ?
If no, why doesn’t it spill out ?
Vertical circular motion
Bucket and water
What kind of motion does the
bucket perform ?
Vertical circular motion
What kind of force provides
the centripetal force Fc to the
bucket ?
Tension T
Weight
mg
Vertical circular motion
Bucket and water
What kind of force provides
the centripetal force Fc to the
bucket at the highest position ?
Fc = T + mg
Tension T
Weight
mg
Vertical circular motion
Bucket and water
What kind of force provides
the centripetal force Fc to the
bucket at the lowest position ?
Fc = T - mg
Tension T
Weight
mg
Vertical circular motion
Bucket and water
What kind of force provides the
centripetal force Fc to the water
at the highest position ?
Fc = R + W
Reaction of
the bucket
R
Weight
of water
W
Vertical circular motion
Bucket and water
What kind of force provides
the centripetal force Fc to the
bucket at the lowest position ?
Fc = R - W
Reaction of
the bucket
R
Weight
of water
W
Vertical circular motion
Loop-the-loop
Vertical circular motion
Loop-the-loop
What kind of force provides
the centripetal force Fc to the mass ?
The reaction of the track
Class exercises
M.C. Exercise
True or False
Main
menu
M.C. Question 1
Which of the following formula
shows Newton’s second Law ?
v = r
=/t
F = ma
a = v2 / r
M.C. Question 2
At which position is the tension
on the bucket largest ?
True or False Question 1
If the angular velocity of the bucket
at the top position is too small,
water may spill out.
True
False
True or False Question 2
In the Ocean Park , cart coast rider
can loop the loop by tension.
True
False
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