Why does a roller coaster
stay on a track upside
down on a loop?
It’s inertia that keeps you in your seat.
Inertia is the force that presses your
body to the outside of the loop as the
train spins around.
• Although gravity is pulling you
toward the earth, at the very top of
the coaster the acceleration force is
stronger than gravity and is pulling
upwards, thus counteracting gravity.
.
DEMO
Uniform Circular Motion
 Uniform circular motion is the
motion of an object in a circle with a
constant or uniform speed
Objects moving in uniform
circular motion will have a
constant speed.
But does this mean that they
will have a constant velocity?
No. Because…
Tangential Velocity
 The best word that can be used
to describe the direction of the velocity vector
is the word tangential.
In geometry, the tangent line (or simply the
tangent) is the straight line that "just
touches" the curve at that point
Tangential Velocity=The
instantaneous linear velocity of a
body moving in a circular path
Calculation of Velocity
Average Speed=
distance
_____
time
=
circumference
___________
time
A ball is whirled on the end of a string with
constant speed when the string breaks.
Which path will the ball take (i.e. what
direction is the tangential velocity vector)
Centripetal Force
 Any object moving in a circle (or along
a circular path) experiences a
centripetal “force”.
 Centripetal means moving or directed
toward a center OR “Center Seeking”
•Centripetal Force - any force that
causes an object to move in a circle
•The word centripetal is merely an
adjective used to describe the
direction of the force.
A centripetal force is always
perpendicular to an object’s motion,
toward the center of the circle when an
object moves
Imagine tying a ball to the
end of a string and twirling
it in a circle over your head.
• The string exerts the centripetal
force on the ball to move it in
a circle.
• The direction of the
pull is toward your hand
at the center of the circle
Centripetal acceleration is the
acceleration of an object moving in a
circle due to the centripetal force.
• This means that the centripetal
acceleration vector is directed
inward in the direction of
movement
Centripetal Acceleration
In circular motion, the acceleration is radially
inward, toward the center of the circle, and
perpendicular to the velocity.
Centripetal Acceleration
http://phet.colorado.edu/en/simulation/ladybugmotion-2d
Centripetal Acceleration
A motorcycle drives around a bend
with a 50-meter radius at 10 m/sec.
Find the motor cycle’s centripetal
acceleration
As a young boy swings a yo-yo parallel to the
ground and above his head, the yo-yo has a
centripetal acceleration of 250 m/s2. If the yo-yo
string is 0.5 m long, what is the yo-yo`s tangential
speed?
A race car moving along a circular track has a
centripetal acceleration of 15. 4 m/s2. If the car
has a tangential speed of 30 m/s. What is the
distance between the car and the center of the
track?