BACKGROUND:
Students may have had trouble
describing some of the motions that were observed during lab. The words
below are very crucial to understanding motion, take care that students
understand the scientific terms, which may be different from the common
usage of the words.
Rotating and spinning both refer to
an object that turns on its axis. The yo-yo, gyroscope, and orbiter can
be described in part as rotating on an axis.
Centripetal force is an inward force
or center seeking force that causes an object to follow a circular path.
Centrifugal force is an outward force, the reaction to centripetal
force. You are sitting in the center of the rear seat of a car. The
driver suddenly turns left rounding a corner, with tires squealing, in a
wide circular arc. You find yourself sliding across the seat to the
right and you remain jammed against the right interior wall of the car
until the driver straightens. Centrifugal force pushes you outward, but
the wall of the car pushes you inward an effect of centripetal force.
Speed is a basic property, and defined as a body
that travels a certain distance in a given time. An automobile for
example, travels so many miles per hour. Speed is simply
the ratio of distance traveled per time (speed = distance/time).
When we describe speed and the
direction of motion we are specifying velocity. If we say that a body
moves at a rate of 40 miles per hour to the north, this is velocity.
Constant velocity implies constant speed and direction. A car on a
circular track may have a constant speed but the velocity is changing.
Any change of speed or velocity is
called acceleration, In a car, acceleration would be called
"pick-up." It is the rate of change, which refers to a
decrease or increase of speed.
PROCEDURE:
Go over the
previous lab materials in more detail, using the
information provided below.
YO-YO - The string is
not tied to the axle but looped around it. Yo-yo reaches the bottom and
the yo-yo keeps rotating. The yo-you keeps spinning (sleeping) until you
"wake it up" by tugging on the string causing it to climb. The
yo-yo rolls down, the string with a constant acceleration as stated in
Newton's second law of motion.
FORCE MACHINE - For
every action there is an opposite and equal reaction. When you lift one
ball the energy is released when it hits the other balls. The energy
goes through the balls and emerges when the last ball releases the
energy. Theoretically the balls should go forever, but the energy will
dissipate because of friction.
BALL - Throwing the
ball up toward space can be explained by Newton's first and second laws.
The ball is thrown and will continue unless friction and gravity didn't
force it down. The second law of motion explains the speed that a
student throws it. Notice that the motion of the ball at the beginning
will be different because each student will accelerate the ball
differently.
BALLOON ON STRING -
The balloon going backwards illustrates that for every action there is
an equal and opposite reaction. The balloon loses air that reacts by
moving along the string.
ORBITER - The orbiter
can rotate on its axis (the string), but the plastic fins are pulled
outward by centrifugal force and inward by centripetal force. The speed
of the axis determines the shape. The faster the spin the greater the
tendency to go outward.
GYROSCOPE - A
gyroscope is a wheel mounted so it can freely rotate in any direction.
Once the wheel is spinning the mount can be turned in any direction and
the wheel will continue to spin in the same plane. Unless an outside
force stops the gyroscope it can continue, even if it looks like it
should fall down.
