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A car moving in a circle is
always turning in the same direction

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Identify the Fc and v.
What is the relationship between Fc and v?

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Cut the Rope

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D. Centripetal Force
(F _{c} ) - force directed toward center of
circle which keeps an object moving in a uniform circular path

F_{c }
=
m a _{c} =
m v ^{2}
r

AP Physics p. 130) 8, 11

Ex) A 5.0 kg object moves
in a circle at a constant speed of 10. m/s. What is the radius of the
object's circular path if the object's centripetal force is 1000. N?

Ex) A
5.0 kg object moves in a
circle at a constant speed of 10. m/s .
What is the radius of
the object's circular path if the object's
centripetal force is
1000. Newtons ?

1000. N =
5.0 kg (10. m/s) ^{2}
r

(1000.) = 500/r

1000r =
500

r = 500/(1000)

r = .50 meters

Image created by John Wetzel, founding author of WikiPremed.
Released under a
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Great Centripetal Force Demo

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E. Changing Centripetal Force

1. F_{c} and Mass?

Put your mouse over each variable above

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Direct Relationship

(Both variables on top)

Mass
F_{c}
x 2
x 2
x 3
x 3
x 4
x 4
x 1/2
x 1/2
x 1/4
x 1/4

2. F_{c} & Radius?

[ Flash ]

Inverse Relationship

(One variable on top,
other on bottom)

F_{c}
r
x 1/2
x 2
x 1/3
x 3
x 1/4
x 4
x 2
x 1/2
x 4
x 1/4

A car moves around a track at constant speed.
When is the acceleration greatest?

What is the acceleration from A to D?

a is greatest from A to B. r is small.

3. F_{c} &
Velocity?

[ Flash ]

Direct Square Relationship

(Both variables on
top,
one is squared)

V
F_{c}
x 2
x 4
x 3
x 9
x 4
x 16
x 1/2
x 1/4
x 1/4
x1/16

2 Step Challenge

Ex) A toy car moves in a circular track of radius 5.00 m in 10.0 seconds.

What is the car's centripetal acceleration?

a _{c} = V ^{2} /r

r = 5.00 m

t = 10.0 sec

a = ?

Need to first find V !!!

V = D d/ D t

V = (2∏r)/t

=
[2∏(5.00 m)]
(10.0 sec)

V = 3.14 m/s

a _{c} = V^{2} /r

a _{c}
= ( 3.14 m/s) ^{2
}
/ (5.00
m)

a _{c}
= 1.97 m/s^{2}

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Hammer Throw

Teaching from Space: Centripetal Force

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This media asset is adapted from video provided by NASA's Teaching From Space program.
Produced bt WNET.org
http://www.teachersdomain.org/resource/npe11.sci.phys.maf.centripetal/

[Circular Motion AP]

ŠTony Mangiacapre.,
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