Transcript Circular Motion

Circular Motion
 = the movement of an object at constant
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speed around a circle with fixed radius
Axis – straight line around which rotation
takes place
Rotation – object turns around an internal
axis
 Ex. Ice skater
Revolution – object turns around an
external axis
 Ex. Earth around the sun
Rotational Speed
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Linear speed – distance/time
Tangential speed – speed along a
circular path
Rotational speed – number of
rotations per unit of time
Example: Carousel horses travel at
same rotational speed but different
tangential speed
Linking tangential and rotational
speed
Tangential speed is
radial distance times
the rotational speed
V = r ω
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Centripetal Force
Force that causes an object to
follow a circular path
 Ex. Force holding occupants
safely in a rotating carnival ride
 Fnet = mv2
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r
Centripetal Acceleration
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Always points toward the center of
the circular motion.
Period (T) = time needed for an
object to make one complete
revolution
Distance traveled = circumference
Circumference = 2πr = πd
Other formulas
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Centripetal Acceleration equals the
velocity squared divided by the radius
Ac = v2/r
The number of revolutions equals the
distance traveled divided by the
circumference
Revolutions = distance/circumference
Sample problems
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If a wheel has a diameter of 0.51
m and the wheel travels for 15 m,
how many revolutions will it
make?
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What is the tension in a 3.2 m
length of string that whirls a 1.5
kg mass at 2.1 m/s in a horizontal
circle?