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REGENTS PHYSICS
STUDENT NOTES-MECHANICS
UNIFORM CIRCULAR MOTION
ROTATION VS REVOLUTION
Rotation- when an object spins about an INTERNAL ___________ .
Examples:
Revolution- when an object spins about an _________________ axis.
Examples:
ROTATIONAL VS LINEAR SPEED
Linear Speed - the speed, in _____________ that the object is moving as it travels in a
circular motion.
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Rotational Speed - is the number of ________________ per unit of time.
Example: “The object rotates three times every second”.
This is also called the _________________ of the object.
The PERIOD is how much time it takes for the object to rotate __________.
Example: The PERIOD of the Earth orbiting the Sun is 365 days.
f= 1
T
Example: Where on a CD would the rotational rate be the greatest?
Where would the linear speed be the greatest?
Name TWO ways that you could you increase your LINEAR speed on a Merry Go
Round.
1. _______________________________________________________
2. _______________________________________________________
Example: Where on Earth do you have the greatest LINEAR speed?
The least LINEAR speed?
Where on Earth do you have the greatest ROTATIONAL speed?
What IS the rotational speed for the Earth?
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UNIFORM CIRCULAR MOTION - any object that travels in a circle at a
_________________ rate of speed.
The velocity changes because the ____________________ is constantly CHANGING.
Acceleration is a change in VELOCITY over time. Therefore an object traveling in
uniform circular motion is ACCELERATING.
How do you determine the acceleration of an object that is NOT changing its speed, but
is changing its direction?
We cannot use a = Vv -Vi
t
This is only used if we have a change in the MAGNITUDE of the velocity.
Instead, we use the following equation if it is an object traveling a constant speed but
changing direction around a circular orbit.
a = v2
r
Describe, using this equation, how you can increase the acceleration of a satellite that is
orbiting the Earth.
In both cases, you are causing the satellite to change ___________________ at a greater
rate.
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WHAT CAUSES AN OBJECT TO TRAVEL IN A CIRCULAR PATH?
Newton’s First Law says that objects will travel at a constant speed in a STRAIGHT
LINE if there is ________ force acting on them.
How can I get an object to accelerate by either speeding up or slowing down?
But objects that travel in circular paths don’t speed up or slow down. Are they
accelerating? Answer is __________ !!!!
So how is the FORCE situated? The answer is that the force is ____________________
to the direction that the object is traveling.
Direction that the object wants
to travel.
Center seeking force.
What do you suppose would be a great example of a center seeking force?
Earth
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The Earth’s __________________ is the center seeking force.
It causes the satellite to constantly change its direction, therefore constantly accelerating.
What would happen if gravity were to disappear?
Would there be any forces acting on the object then?
ANOTHER EXAMPLE OF UNIFORM CIRCULAR MOTION
Nucleus
of an atom
An ______________________ FORCE causes the electron to travel in a circular motion.
We call any FORCE that causes an object to travel in a circular orbit a “CENTER
SEEKING FORCE”.
Other examples of “Center Seeking Forces” that cause circular motion are…

Frictional Forces – for example, a car going around a corner.

Tensional Forces- for example, a bucket being swung around on a rope.
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THESE ARE ALL “CENTER SEEKING FORCES”, SOMETIMES CALLED
CENTRIPITAL FORCES.
If gravity pulls satellites towards the earth with a centripetal force, then
why don’t satellites crash to Earth?
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The formula for CENTRIPITAL FORCE is a follows…
a = v2
r
F = ma
 F = m v2
r
m is the mass of the satellite. A satellite is anything that travels in a circular path.
SAMPLE PROBLEM: You decide to ride the “Mad Mouse” in Fantasyland on your
Senior Class trip to Disney world. You find yourself hanging on for dear life due to a
technical error with the ride. Your distance from the center of the ride is 3 meters and you
make 10 rotations in 18.25 seconds. You have a mass of 50 kilograms.
(1) Draw a diagram of the situation!
(2) Determine the Period of Rotation.
(3) Determine your linear speed.
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(4) What is your centripetal acceleration?
(5) Calculate the centripetal force that is keeping you from flying off the “Mad
Mouse”.
(6) What is the TYPE of centripetal force that is preventing you from flying off the
“Mad Mouse”?
(7) What would happen if there is not enough “centripetal force” to keep you on the
ride?
(8) What is the direction of the centripetal force? The centripetal acceleration? The
change in velocity? The instantaneous velocity?