Physics 12 Lab – Centripetal Force
SAFETY GLASSES MUST BE WORN BY ALL STUDENTS DURING THE WHOLE LAB PERIOD!
Purpose: to investigate the relationship between the centripetal force and the mass of an object in circular motion as well as the relationship between centripetal force and the velocity of the object in motion.
Apparatus: glass tube wrapped with masking tape OR plastic tube, string, 4 rubber stoppers, masses, stopwatch, meterstick, object to mark position.
Procedure:
1. Find the mass of the rubber stopper.
2. Attach a string securely to the rubber stopper. Pass the free end through the tube and attach a mass to that end.
3. Adjust the string so that the radius of the horizontal circle produced by whirling the stopper will remain constant. Attach a marker to the string just below the bottom of the tube. It should NOT touch the tube. It is a visual so you know that the radius of the string is remaining constant.
4. While supporting the mass in one hand, whirl the stopper by moving your other hand in circular motion. Release the mass you are holding slowly and adjust the speed of the stopper so that the marker remains just at the bottom of the tube.
Do a few practice trials before recording any results.
Part A:
When you are ready, find the time needed fro 20 complete revolutions. Remember that the period is the time for 1 revolution. Stop the motion and measure the radius of the circle. Measure it from the center of the tube to the center of the stopper. Calculate the velocity in m/s and record.
Do the experiment for a 100 g, 200 g, 300 g, and 400 g mass. Be sure to take three time trials and find the average time for each mass.
Plot a graph of Fc (hanging weight) vs velocity.
Plot a graph of Fc (hanging weight) vs velocity squared.
Part B:
Using the 100 g hanging mass, vary the radius of the horizontal circle. You already have one piece of data from part A. Do the experiment for 4 more radii (vary the radius from 30 cm to 80 cm averaging the three time trials for each radius). Calculate the velocity in m/s and record.
Plot a graph of velocity squared vs radius.
Part C:
Keep the radius constant (use the radius from part A) and keep a 200 g mass at the end of the cord, but vary the size (mass) of the rubber stopper. To get a wide range of mass for the stopper, use one stopper (should be the data from part A), then two stoppers, three, and four. Take three time trials for each mass and average the time. Calculate the velocity in m/s and record.
Plot a graph of velocity versus mass of the stoppers.
Questions:
1. From the graph, what is the suggested relationship between Fc (hanging weight) and the velocity of the stopper?
2. What is the suggested relationship between the velocity squared and the radius of revolution?
3. How would you expect the velocity to change as the mass increased given the same force and radius?
4. From your first graph, compare the slope of Fc (hanging weight) vs velocity squared with the ratio of the mass/radius.
Note: using the equation to analyse the questions could prove VERY helpful.
Please make your own data and analysis table.