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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 speedof an object experiencing UCM?
T is the time for one cycle, aka, the period.
Since we are talking about a circular path this equation would change to:
• v = d/t• v = (circumference of circle)
(time to travel around the circle’s path)
v = 2 π r units: (m)T (s)
T = Period = the time for one complete cycle or the time for one complete revolution.Units: seconds/cycle or just seconds.
f = frequency = the amount of cycles (or revolutions) completed in a certain amount of time (usually one second).Units: cycles/second or Hertz (Hz)
Period and frequency are inverses of each other: T = 1/f
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 magnitude of 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 always directed 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.
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=relatedhttp://www.youtube.com/watch?v=EnyKq7pO-c8&feature=related
https://www.youtube.com/watch?v=bpFK2VCRHUs
Go here to watch some videos… but have your earbuds plugged into your ears, please.