Physics 221
Pre-lab assignment: This is a hybrid of a verification and discovery lab. You will, along with your group, design a “modified Atwood machine”. Write the names, title, objectives, introduction and the answer to the prelab question. As usual, you will be writing the procedure as you perform the lab, as well as updating the equipment list and taking data. Your notebook will be checked off during lab, and the photocopy of the pages is due on Thursday, February 25.
Your full name
Your partners’ names
Lab 6: Designing and executing a modified Atwood machine
Objectives:
• Designing an experiment based on theoretical calculations
• Setting up familiar and new lab equipment to measure familiar quantities
•Verification of the prediction made from the theory
Introduction:
This is a schematic drawing of a modified Atwood machine:
m2 will fall, towing m1 along. Knowing both masses, it should be a simple thing to calculate the tension force in the connecting wire and the acceleration of both masses.
You will use a Vernier Wireless Dynamics Sensor System (WDSS) that is a force sensor and an accelerometer in one device. It communicates data via Bluetooth to a laptop or the datalogger.
Prelab question
Together with your team, determine the two masses that you will use for this experiment. The only limitations are that m1 must be at least the mass of the cart plus the WDSS device (and various bolts), and that the acceleration must be slow enough so that you can obtain at least ten “good” data points. Calculate the tension and acceleration expected from your masses — show the complete detail from the free-body diagrams, to the force equations, to the solution.
Equipment: (As always, note any deletions or additions)
2.3-meter metal ramp
Vernier Wireless Dynamics Sensor System (WDSS)
Collision cart
Safety precautions:
To avoid damage to the force sensor, never exceed 50 N on the sensor.
Notes on the procedure(don’t put these in your notebook, but I want you to consider them as you write the procedure):
1. Does the manual say if you have to zero or calibrate either the accelerometer or the force sensor?
2. What device will you wirelessly send the data to? What software do you need on that device? What steps must you take on that device to ready that device to receive data?
3. What did you use to connect the two masses? What did you use at the end of the ramp to lower friction?
4. How will you review the data to make sure you have at least 10 “good” data points? (For instance, a graph is a nice way to visualize the acceleration – on what device/software will you view such a graph during lab?)
Data section
Record both masses (and units)
Record the uncertainties (they are called the “resolution” in the manual) of the force sensor and the accelerometer.
Pastethe “good” data points in table format in your lab notebook with appropriate headings. Pay attention to units and sig figs.
Graph and analysis
Attach or make a graph in your notebook that plots time (x-axis) versus force (y-axis). On a different graph, plot time (x-axis) versus acceleration (y-axis). Pay attention to each title, tick marks, units and labels.
Draw the x- and y-error bars on the points for each graph, based on the instrument uncertainties for the timer, theaccelerometer and the force sensor. If either or both are too small to plot, state that clearly on the graph.
Results
Clearly state the predicted tension and acceleration. Pay attention to units and sig figs.
Clearly state the measured tension and acceleration, along with their uncertainties, in the usual format.
Conclusion
Were your results consistent with your prediction? If they are, clearly state how the measured quantity is consistent with the predicted quantity. If they are not, clearly state how the measured quantity is not consistent with the predicted quantity. Remember, it can be the case where the acceleration is consistent but the force is not.
Calculate a percent error for both the tension and the acceleration, using the predicted quantity as the “published” value.
Is this a “good” lab for students to demonstrate a modified Atwood machine? Is the WDSS device a good device for this lab? Whether you answered “yes” or “no” to either question, use your results and your experience to state at least one good thing about the setup and one improvement the setup could use.