force and motion-ii: continued friction and drag;circular motion
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Force and Motion-II: continued Friction and Drag;Circular Motion. Lecture 6 Monday:2 February 2004. UNIFORM CIRCULAR MOTION. CIRCULAR MOTION. When an object travels in a circle, its velocity is constantly changing (in direction-at least). - PowerPoint PPT PresentationTRANSCRIPT
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Force and Motion-II: continued
Friction and Drag;Circular Motion
Lecture 6
Monday:2 February 2004
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UNIFORM CIRCULAR MOTION
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CIRCULAR MOTION
• When an object travels in a circle, its velocity is constantly changing (in direction-at least).
• That means the object has a non-zero acceleration even if it moves at constant speed.
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What is the direction of this acceleration?
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Acceleration in Circular Motion
Centripetal acceleration:• Direction:
Toward the center of the circle
• Magnitude:
av
r
2
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FORCES IN CIRCULAR MOTION
• An “unbalanced” force must cause the acceleration.
center. the towardisdirection theand
and
2
2
r
vmF
r
vaamF
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Using Freebody Diagrams to Analyze Forces
Twirl a ball attached to a string in a vertical circle. What forces act on the ball and what are the direction of these forces?
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Using Freebody Diagrams to Analyze Forces
What forces act on the ball and what are the direction of these forces?
Top
Bottom
T
T
W
W
a
a
Are we missing a force?
(the centripetal force)?
Is the acceleration =g?
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Using Freebody Diagrams to Analyze Forces
What forces act on the ball and what are the direction of these forces?
Top
Bottom
T
T
W
W
a
aAre we missing a force?
(the centripetal force)?
Is the acceleration =g?
-T-W=m(-a) or
T+W=ma
T-W=ma
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Any force can be a “centripetal” force.
-Gravitational Attraction
-Tension in a string
-Normal Force
-A push or pull…
Does the planet in orbit here have a gravitational force AND a centripetal force acting on it?
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PERIOD IN CIRCULAR MOTION
vr2
T Period so
2revolution onefor time
2time
positionVelocity and
r2 nceCircumfera
Trr
v
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