Download Circular Motion

Circular Motion
Uniform circular motion (UCM)
is the motion of an object in a perfect circle
with a constant (or uniform) speed.
• Another example of this would be you driving in a
perfect circle at a constant speed.
• Are you accelerating? Constant or changing?
• Do you feel pushed? Is there a force causing you
to accelerate?
What is the equation to find the speed
of an object experiencing UCM?
• v = d/t
• v = (circumference of circle)
(time to travel around the circle’s path)
Since we are talking about a circular path this
equation would change to:
v=2πr
T
units: (m)
(s)
T is the time for one cycle, aka, the period.
How would you describe the velocity
in this situation where an object
is moving in a circle?
• The velocity of an object
moving in a circle is
constantly changing!
• We say the velocity
vector is Tangent to the
circular path of travel and
call it the Tangential
velocity.
Since the velocity is changing we can say
an object moving in a circle is accelerating.
• Since the velocity is changing at a constant
rate, we can say the acceleration is
constant for an object experiencing
Uniform Circular Motion.
• What is the direction of the acceleration?
• Show accelerometer on turn table!
• Acceleration is inward toward the center
of the circular path!
• Called Centripetal Acceleration!
• (centripetal = center-seeking)
Remember from Newton’s First and Second Law,
if there is a change in velocity there must be
an outside force causing this acceleration.
• When you spin a bucket of
water around your head,
what direction do you apply
a force on the bucket?
Remember from Newton’s Second Law:
the direction of the net force is always the
same as the direction of the acceleration!
The force causing an object to
move in a circular path is an
inward seeking force and is
called the Centripetal Force.
Centripetal = center seeking
Do not confuse this with Centrifugal Force
which is a description for the FEELING of
being pushed outward.(fake!)
Centripetal – inward (center)
seeking, real.
Centrifugal – outward fleeing,
fake.
The Math
This is it for the math
Force centripetal can be
provided by…
• Tension Force (the tension in a string or
rope)
• Friction Force (the friction between tires
and road, or shoe and ground)
• Gravity Force (Earth experiences a force
due to gravity while moving around the sun)
• Walls of a ride (amusement park ride)
http://www.youtube.com/watch?v=GauoEdyMZwY&feature=related
http://www.youtube.com/watch?v=EnyKq7pO-c8&feature=related