Circular Acceleration - CBL
When an object is in uniform circular motion, there is a net force
and resulting acceleration involved because this is a non-inertial
frame of reference. Textbooks demonstrate that the acceleration and
the resulting net force is directed radially inward, having a value
ac = v2/R
Any acceleration along the tangent (perpendicular to the radius)
occurs only while speeding up or slowing down. If the circular motion
is uniform, the speed is constant, there is no tangential
- Use a CBL to show that the acceleration in constant circular
motion is directed inward rather than along the tangent.
- Determine that the acceleration is directly proportional to
the radius for a platform which is rotating.
Bicycle wheel mounted so it spinsaround a vertical
Boards to mount equipment onto bicycle wheel
(2) 3-axis Accelerometers
TI Graphing Calculator
(3) DIN-CBL Adapters
- If one travels in a circular path at a constant speed, he/she
feels a force. In which direction does this force appear to be
- If one travels in a circular path at a constant speed, what is
his/her acceleration in their direction of motion? Explain. What
is their direction of motion at any time?
- Mount the CBL and accelerometers as shown in the diagrams. For
both accelerometers, the axes that are aligned with the radius
should be pointing the same direction, with outward being
- Connect the tangential direction of the outer accelerometer to
CH1. Connect the radial direction of the outer accelerometer to
CH2. Connect the radial direction of the inner accelerometer to
- Run the program GRTAM96. Choose 3-AXIS from the choice of
accelerometers. Choose PRACTICE from the menu, which gathers 90
data points, 0.1 second apart.
- Once the program has loaded up the CBL, and it says "READY",
disconnect the TI-82 from the CBL.
- Start the wheel into motion. With practice, you will be able
to reach in and press the TRIGGER button on the CBL. This
initiates the data collection, which will continue for 9
- Once the data collection is complete, stop the wheel and
re-connect the TI-92 to the CBL. Press [ON] on the TI-82
to halt the program, choosing QUIT at the prompt. Run the program
- DOWNLOAD will ask several questions. You have collected data
from 3 channels, and you have recorded time.
- Once DOWNLOAD has finished, only a matter of a second or two,
you will have the following data to work with:
- L1 = Time
L2 = Tangential Acceleration
L3 = Outer Radial acceleration
L4 = Inner Radial acceleration
- Plot the graphs as shown here to examine the data you have
- L1 vs L2 - shows the tangential acceleration (should be
L1 vs L3 - shows the acceleration along the radius is large
L1 vs L3 and L4 - shows the relationship between radius and
- If one uses two accelerometers in a CBL case, mounted along
the length and width of the case, the procedure above can be
repeated with the experimenter holding the case at arm's length
and spinning. This doesn't yield the radial dependence of the
acceleration, but shows the tangential vs the radial very
- The data can be downloaded into Graphical Analysis (Vernier)
and plotted using a computer. This makes it convenient for
printing out the results.
- We have used two 1/4" plywood boards that we taped to the
spokes of a bicycle wheel. Actually, we used the heavy wheel used
for gyroscope demonstrations.
- We have also mounted velcro pads on one side to accept the
velcro pads we place on the bottom of the 3-axis accelerometers.
This makes for convenient mounting, and we use this technique
throughout our labs.
Gunn High School