4 Lab 4: Momentum and Impulse

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 4

Momentum and Impulse

What you will do:

Drop your phone onto a soft surface. Then use the accelerometer that is built in the phone to study the relation between the momentum before a collision and the impulse of the collision.

What you will need:

• A smart phone installed with the Phyphox app
• A soft and inelastic surface (such as a thick blanket)

Demonstration Video: https://youtu.be/3Mrl84QVYNs

Procedures:

1. In the Phyphox app, open the “acceleration with g” sensor.
2. Start an acceleration with g measurement.
3. Hold the phone still for at least 2 seconds at 20 cm above the soft surface with the back of the phone facing vertically down. Then release the phone and let the phone fall onto the soft surface. (If the phone was significantly bounced back by the surface, you should choose a softer surface.)
4. Stop the measurement. Among the X/Y/Z acceleration graphs, identify the graph that corresponds to the vertical direction. The largest peak on this graph should be more than 5 times larger than the largest peak on the other graphs. If there is no such graph, repeat the drop while making sure the phone is released flat and then falling onto a flat, soft surface.
5. Use the graph of the vertical acceleration to identify the time points at which the phone (a) just got released from the hand, (b) just came in contact with the surface, (c) just reached the maximum displacement into the soft surface.
6. Export the data as a csv file.
7. Repeat Steps 3 – 6 above for a total of 3 times (keep the dropping height at 20 cm).
8. Repeat Steps 3 – 6 above for dropping heights of 30 cm and 40 cm (one drop for each height).
9. Use one data set as an example, explain how you determined each time point in Step 5.
10. Open any one csv file in Excel. Use the absolute acceleration data in the file to calculate the average gravitational acceleration g of the phone while the phone is stationary. Describe which segment of data were used to compute g.
11. In each csv file, create a new column that equals the column of the measured vertical acceleration minus the average gravitational acceleration g (which is obtained in Step 10). The reason for this step is to obtain the acceleration relative to the surface of the Earth.
12. In each csv file, select the entire table. Then change the number formatting to show at least 5 decimal places. Save the new csv file for later analysis.
13. For each drop, use the Curve Integrator (Python program) provided by the course instructor to calculate (a) the speed of the phone before getting into contact with the surface, and (b) the impulse that the surface applied to the phone before the phone comes to a stop for the first time. (You will need to search online for the mass of your phone.)
14. Compare the momentum of the phone before hitting the surface with the impulse from the surface. Discuss if the result matches your expectations. (Hints: Should you use the absolute acceleration to integrate for momentum and impulse? Can you choose the time points in Step 5 differently with a justification?)
15. Compare the maximum forces that the surface applies on the phone when the phone was dropped from different heights. Discuss if the result matches your expectations.
16. (Bonus) In this experiment, the soft inelastic surface might not be an ideal choice. If we use an elastic surface (so that the phone will be bounced back up), how would you determine the time point of the maximum displacement (Step 5, Part c)? You can do a quick trial to verify your hypothesis. Be careful not to damage your phone!

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 in the results section. Show a sample calculation of your error propagation in the appendix.
• Identify the sources of error in your measurements.
• 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 4” 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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