1 Lab 1: Free Fall

Acknowledgment

This project is made possible with funding by the Government of Ontario and through eCampusOntario’s support of the Virtual Learning Strategy. To learn more about the Virtual Learning Strategy visit: https://vls.ecampusontario.ca.

PHY136 Stay-At-home Experiment 1

Measuring the Free Fall Motion of a Cell Phone

What you will do:

Using the accelerometer that is built in the phone to analyze the kinematics of a free fall motion.

What you will need:

• A smart phone installed with the Phyphox app
• A soft surface for the phone to fall onto (e.g. bed, couch, blanket etc)
• A ruler or a measuring tape

Demonstration Video: https://youtu.be/JrQ6v0oIxHg

Procedures

1. In the Phyphox app, open the “acceleration with g” sensor.
2. On your computer, you may use the web browser to remotely access your Phyphox app. Through remote access, you can save the data measured by the phone to your computer as a “.csv” file. Alternatively, you may save the data on your phone first, then transfer the data file to your computer.
3. Start a measurement of acceleration with g. Hold the phone stationary with different orientations, and use the change in the acceleration on the x/y/z direction to determine the correspondence between the directions of x/y/z in the data and the directions of height/width/thickness on the phone. Take a screenshot of the acceleration readings, and use the screenshot to describe how you determined the directions.
4. Hold the phone at 10 cm above the soft surface. (Question: should the 10cm be measured from the bottom, the center, or the top of the phone? Why?) If you are using a measuring tape to measure height, it may be a good idea to fix the bottom of the tape to another object (such as tying it to a cardboard box using an elastic band). Keep the phone vertical, start an acceleration without g measurement, release the phone and allow the phone to free fall onto the soft surface. If your surface is bouncy, be extra careful not to let your phone fall to the floor!
5. Repeat free falling from the same height for a total of 5 times.
6. Stop the measurement. On the cellphone screen, navigate to the “absolute” acceleration tab, use the “Pan & Zoom” tool and the “Pick Data” tool to locate the time points of the beginning and the end of each free fall of the phone. Note down these two time points and the absolute acceleration at these time points to help you later interpret the data file.
7. Export the data as a csv file (comma, decimal point), then clear the current data.
8. Repeat steps 4-6 above for drop heights of 15cm, 20cm, 25cm, 30cm.
9. For each drop, measure the acceleration of the phone during free fall (i.e. read the absolute acceleration at the beginning and the end of the free fall, and take the average of the two. If you have cleared the data on the phone, you can always use the csv file to retrieve the values.)
10. For each drop height, calculate the average acceleration during the free fall using the 5 repeats.
11. For each drop height, calculate the average duration of free fall using the 5 repeats.
12. For each drop height, use the height and the known value of g = 9.81 m/s2 to calculate the speed of your phone just before it hits the soft surface.
13. For each drop height, use the time of free fall and the measured gravitational acceleration (your experimental results) to calculate the speed of the phone before hitting the soft surface.
14. Plot the calculated vs experimental speeds you found in Steps 13 and 14 (you should have one data point for each different height). What do you expect the slope of this line to be? How does the slope of your graph compare?
    Remember to report the uncertainty of the slope and include error bars on your plot. The uncertainty can be from the regression analysis or from the limiting slopes method. You should report the larger of the two.
15. Plot the drop height against the square of the time of free fall to find the gravitational acceleration. (Question: is this result more accurate than the acceleration values that you read in Step 10? Explain your findings.)
16. Release the phone from 30cm height with the back of the phone facing down. Can you identify the effect of air resistance in your accelerometer data? Based on your data, is the air resistance a constant force?

Tips for data analysis:

• Complete all calculations that are required in the procedures above. Show sample calculations in the appendix.
• Answer all questions in the procedures section above.
• Attach graphs or tables when necessary.
• If you write a program for calculations, attach the code in the appendix.

Suggested topics for discussion:

• Find the uncertainty values for each calculation you did in this lab. Show a sample calculation of your error propagation in the appendix.
• Identify the sources of error in your measurements. (“Human error” does not count. This is why we record measurement errors!)
• Feel free to do more tests to verify your claims if possible.
• Make a reasonable conclusion based on your results.
• Compare your results with literature values (and add citations). You may reference the textbook.
• What other quantities can be determined with the same experimental design?
• What can be done to reduce the uncertainties at no cost while staying at home?

We value your feedback!

Did you enjoy this experiment? What are the aspects that you dislike the most about this experiment? – Let me know in the “Student Feedback Survey for Lab 1” on the discussion board on Quercus! We may award the most helpful inputs with +1 bonus mark for the lab report!

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