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Mr. Borosky
Physics Section 6.2 Notes
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Section 6.2 Circular Motion
Objectives
Explain why an object moving in a circle at a constant speed is
accelerated.
Describe how centripetal acceleration depends upon the object’s
speed and the radius of the circle.
Identify the force that causes centripetal acceleration.
Read intro paragraph p. 153
Acceleration deals with a change in velocity (vector quantity thus
magnitude and DIRECTION) divided by a change in time, thus something
that is moving around in a circle at a constant speed has
acceleration since the direction is changing.
DESCRIBING CIRCULAR MOTION
Read Section.
Uniform Circular Motion – the movement of an object or particle
trajectory at a constant speed around a circle with a fixed radius.
v
=
Δd / Δt
=
Δr / Δt
Tangent – a straight line or plane that touches a curve or curved
surface at a point but does not intersect it at that point
As the velocity vector moves around the circle, its direction
changes but its length remains the same.
a
=
Δv / Δt
Acceleration vector of an object in uniform circular motion always
points toward the center of the circle.
Centripetal – a quantity that always points toward the center of a
circle; center seeking; it was originated by Sir Isaac Newton.
Centripetal Acceleration – the Center Seeking acceleration of an
object moving in a circle at constant speed.
Physics Principals and Problems © 2005 Started 2006-2007 School Year
Mr. Borosky
Physics Section 6.2 Notes
Page 2 of 2
CENTRIPETAL ACCELERATION
Read Section.
Centripetal Acceleration – the Center Seeking acceleration of an
object moving in a circle at constant speed. It always points
toward the center of the circle. Its magnitude is equal to the
square of the speed divided by the radius of motion.
ac = v2 / r
Period – the time needed for an object to make one complete
revolution. It is denoted by T.
Velocity of an object traveling around a circle can be found by
v = 2Πr / T
And because of that we can find the Acceleration by
ac = 4Π2r / T2
Centripetal Force – the net force exerted toward the center of the
circle that causes an object to have a centripetal acceleration. It
is equal to the mass of the object times its centripetal
acceleration.
Fc = mac
Do
ac
ac
ac
ac
Example Problem 2 p. 155
= 4Π2r / T2
= 4Π2(.93) / (1.18)2
= 36.68 / 1.3924
= 26.34 m/s2
Then
FT = Fc = mac
FT = .013(26.34)
FT = .342 N
Do Practice Problems p. 156 # 12-15
A NONEXISTENT FORCE
Read Section.
Remember Newton’s First Law states that an object at rest will stay
at rest and an object in motion will stay in motion unless acted on
by an outside force.
Go over example of the car and turning.
Centrifugal Force – an outward force.
not exist.
It is fictitious.
It does
Do 6.2 Section Review p. 156 # 16-21
Physics Principals and Problems © 2005 Started 2006-2007 School Year