The document discusses rotational and revolving motion. It defines rotate as turning about an internal axis, and revolve as turning about an external axis. It provides the example that planets both revolve around the sun and rotate about their own axis. The document then focuses on revolving motion, noting that the velocity vector is always tangent to the circle while the acceleration vector always points toward the center. It provides the equation for centripetal force as F = mv2/r.

2.  Objects can ROTATE like the earth on its own axis.
Rotate: turn about
an internal axis
Objects can REVOLVE like people on a ride at Great
America.
Revolution: turn about
an external axis.

3. Objects can also do both at the
same time: Like the planets in our
solar system.
The planets REVOLVE
around the sun and
ROTATE about their
own axis.
What rides at Great America do both?
Our lesson for this session will only deal with revolutions
on a circle. No rotations.

4. As the lady bug revolves around
The circle what do you notice about
The velocity vector?
What do you notice about the The acceleration vector
Acceleration vector? always points toward
the center. This is
The velocity vector is
called centripetal
always a straight line
acceleration.
or linear off the
circle. This is a
tangent line. So
this type of
velocity is called
linear or
tangential velocity.

5. Now lets get active to learn about the following terms:
1. Angular velocity,
2. tangential velocity,
3. Centripetal acceleration
Go to the website and click on the ladybug animation.
Have your guided practice available so you can use the
animation and collect some pieces of information.
http://www.cabrillo.edu/~jmccullough/Physics/Circular_Motion.html#

6. Centripetal means “center-seeking” and centripetal force is not
a new special kind of force. It comes in many forms such as tension
and friction.
Objects moving in a circle experience a center seeking force called
centripetal force.
When the bucket is at the top of the circle it does not fall
out. Why not? The answer is in Newton’s First Law.
Think inertia.
The FORCE on the bucket IS toward the center.
The tether ball’s tension in the rope is divided into an upward
Y force and a center-seeking x force. So the x force is the
Centripetal force.

7. No matter where the car is on
the curve it will experience
the center seeking force called
centripetal force.
Friction keeps the car on the curve.
If there was no friction which
way would the car slide?
The friction is the centripetal force.
Centripetal
force

8. Remember Newton’s Second Law?
F=mxa
This applies to circular motion as well except that
the acceleration has a different formula because its
circular motion.
So for circular motion F = m * ( v2 / r )
F = force
m = mass
v = linear (tangential velocity)
r = radius of circle.

9.  A 5 kg object rotates on a string with a velocity
of 3 m/s and a radius of 1.5 m. What is
 the force on the object?
 F = m * v2 /r
m = 5 kg v = 3 m/s r = 1.5 m
 F = 5 * 32/1.5
 Ans: 30 N