Design a procedure to test how a certain variable (of your choice) may affect a twisting. As always, this should design lab should include….. Defining the Problem and selecting variables: Controlling the Variables: Developing a method for collecting data: Thus, step by step instructions and diagrams are helpful to the reader and highly recommended.
Also include a hypothesis and a sketch graph of what you think will happen.The above information was given to the student by the instructor. What follows immediately below is the student’s own work.
Problem: How does increasing the number of coins on the ruler affect the time it takes for the torsional pendulum to complete one period? Hypothesis: As number of coins on the ruler increases, the time to complete one period will also increase. This is because it takes more force to move a heavier mass.Because the simple equation of circular motion is , the distance between coin and center of mass (radius) is kept constant, and the amount of initial force applied to the ruler (the number of twists and rubber bands) is kept as constant as possible throughout the lab, as mass increases, velocity must decrease; this will increase the time for each period. Also, since the equation for force above can be rearranged to , perhaps the rate of increase of period over mass will slow down as mass keeps increasing, such as pictured in the graph above (like a square root graph).Variables: Independent – number of coins on ruler (mass) Dependent – time duration for 1 period Control – ruler (flexibility, length, mass) – center mass (mass, location on ruler) – rubber band (elasticity, length, and number of) – unfortunately the rubber band naturally stretches when more mass is added on the ruler, which may violate the control variable by changing the elastic force and length of rubber band, however, not much can be done besides choosing a thicker rubber band that is not very easily stretched to use throughout the experiment.Number of twists on rubber band (initial elastic potential force applied to ruler) – distance from center of ruler to coins (both stacks of coins have to be evenly spaced from center of ruler and stay at that distance) – balance (e.g.
number of coins on each side must be the same) – outside unbalanced forces (e.g. do not bump the spinning ruler into things or let a significantly strong wind affect its movement)Ttype of coins (so that increase of mass each time is close to constant) – amount of sticky tacks to stick each coin (so that increase of mass each time is close to constant) Procedure: 1. Set up all materials as pictured above: tape the weight to the middle of the ruler; loop rubber band onto the hook of the mass; however, do not stick coins yet at this point.
2. Twist the rubber band 5 full rotations and keep it from unwinding.3. If you have a partner (Steve, for example), let one person be in charge of holding the torsional pendulum as it unwinds and the other in charge of timing with stopwatch and recording time. Start stopwatch and release the pendulum to unwind at the same time.4. Let the pendulum “spin” for one period: rotating (unwinding and winding) in one direction, turn around, and spinning the opposite direction – all 1 time.
Stop the stopwatch after the pendulum slows down and just about to turn the other direction again. Record this time as “duration of period (seconds); trial 1” in the data table below (after procedure). 5. Repeat steps 2 through 4 if time allows, and record the second time under “trial 2”.
6. Using a small piece of sticky tack, stick 1 one-peso coin on each end of the ruler (total of 2 coins). Make sure both are really at the ends of the ruler, and thus the same distance away from the center of ruler (to keep the ruler balanced). Using this new number of coins, repeat steps 2 through 5.
7. Keep repeating the main experiment (steps 2 through 6) until a total of 30 one-peso coins are used (15 coins on each side of the ruler). Make sure to keep control variables constant (for example, if rotating ruler bumps into something, repeat the trial). Using obtained time durations, process data and draw conclusions about the correlation between increase in mass and change in duration of 1 period.