Introductory Experiment: Force and Pendulums
You will need a 2- or 3-liter soft drink bottle and about 3 meters of string
strong enough to support it, plus the rubber bands and other items you should have
received after purchasing the CD's.
See Making the Pendulum and
Pulling Back the Pendulum on the Gen1 CD directly under the Physics Video Clips heading.
Set up your experiment:
- Make a pendulum using a soft drink
bottle full of water, preferably 2 or 3 liters, though a 1-liter bottle will work:
- Suspend the bottle using strings
tied around the neck of the bottle, as shown on the video clip. The length of the pendulum
should be at least 4 feet, though 6 feet or more would be better.
- Determine the position of the single
string just above the bottle when the bottle is hanging in its natural equilibrium
position.
Obtain data:
- Using your calibrated rubber band, pull the pendulum back until the rubber band
has stretched a length of 9.0 cm, and determine how far the supporting string has moved
from its equilibrium position.
- Pull the pendulum back until the rubber band has stretched to length 9.5 cm, and
determine how far the string has moved from its equilibrium position.
- Repeat until the rubber band has stretched to 11.5 cm length.
Organize and Analyze your Data:
- Organize your string displacement vs. rubber band length in a table.
- The string displacement is the distance of the string from the equilibrium
position.
- Be sure to also record any other data that might be relevant to the results
(e.g., the capacity of the bottle, the length of the pendulum from its point of suspension
to the middle of the bottle, etc.).
- Using smooth curve on the the calibration graph you have constructed for the
rubber band, determine the force exerted by the rubber band at each string displacement.
- Make a table of force vs. string displacement, and make a graph of force vs.
string displacement.
Submit your results:
- Describe how you set the system up in order to get accurate measurements of the
position of the string.
- Specify the capacity of the bottle
and the length of the string supporting the bottle.
- Include your table of rubber band
length vs. string displacement, and a table showing force vs. string displacment (you may
combine all this information into a single table if you wish).
- Do the points on your graph tend to
lie along a straight line, or does your graph appear to have some consistent type of
curvature?