Force and Motion-II: continued Friction and Drag;Circular Motion
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Transcript of Force and Motion-II: continued Friction and Drag;Circular Motion
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).
• That means the object has a non-zero acceleration even if it moves at constant speed.
What is the direction of this acceleration?
Acceleration in Circular Motion
Centripetal acceleration:• Direction:
Toward the center of the circle
• Magnitude:
av
r
2
FORCES IN CIRCULAR MOTION
• An “unbalanced” force must cause the acceleration.
center. the towardisdirection theand
and
2
2
r
vmF
r
vaamF
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?
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?
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
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?
PERIOD IN CIRCULAR MOTION
vr2
T Period so
2revolution onefor time
2time
positionVelocity and
r2 nceCircumfera
Trr
v