Pre-Engineering Physics 1
Centripetal Force Lab
Background: Acceleration and velocity are vectors. Remember vectors have magnitude and
direction. In circular motion, if an
object is moving at a constant speed, yet changing direction as it moves around
it’s circular path it is accelerating.
Every accelerating object must have some force acting
upon it and the force must be in the direction of the acceleration. A centripetal force points toward the center
of the circular path. In the case of the
Moon orbiting the Earth, the centripetal acceleration is provided by the
gravitational attraction of the Earth.
For an electron orbiting a nucleus, the centripetal acceleration is
provided by electrostatic attraction.
Problem: Use the following equipment to make
quantitative measurements of circular motion and find the magnitude of the
centripetal force on a string.
hollow cylinder as handle
washer/weights ( and triple beam balance) in groups of 5, 10, 15, 20
two-hole rubber stopper
2 paper clips
string (and meter stick)-1 meter
stopwatch
Procedure:
Assemble the apparatus as shown in the diagram.
Your instructor will demonstrate the operation of the
apparatus. Among your group, assemble
apparatus, and practice safely swinging apparatus. Take turns getting the feel of the
apparatus. Slowly begin to swing the
rubber stopper overhead. Increase the
speed of the rotation until the marking paper clip is just below the bottom of
the handle. Don’t let the paper clip
marker touch the bottom of the handle.
The centripetal force and the weight (not mass) of the washers are in
equilibrium when the paper clip marker is stationary during this rotation. The tension in the string is equivalent to
the centripetal force.
Data Collection and
Calculations:
Make quantitative measurements and/or
calculations for the following parameters and organize into a data table (one
group member may go to computer lab and make blank tables for each group
member). In 4 different trials (using
groups of 5, 10, 15 and 20 washers), measure the following:
1) mass (m) of
washers
2) time (t) for
5 revolutions
3) radius (r)
when equilibrium is reached
Then make calculations to find the
following:
4) period (T)
5) weight of
washers
6) circumference
of circular path
7) tangential
speed (vt)
8) centripetal
force (Fc)
We know that
Important facts:
Displacement around a circle is the
circumference=2pr
Time for one revolution is the period (T)
Velocity is displacement divided by time
Presentation
of Conclusions: Complete a
data table with your measurements and calculations and attach behind. Each group member needs to turn in this lab
instruction sheet with a completed data table attached behind. Make sure units are evident in the table
for each parameter.
After data collection and calculations, mathematically
derive