2 Lab 2: Friction and Slope
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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 2
Friction and Slope
What you will do:
Let your phone slide down a slope. Using the accelerometer that is built in the phone to measure the coefficients of static friction and kinetic friction between the phone and the slope.
What you will need:
- A smart phone installed with the Phyphox app
- A flat solid board acting as a slope (such as a cardboard box, a hardcover book, a cut board, etc.)
- A bag that can hold your phone
- A ruler or a measuring tape
Theoretical Preparation
The “acceleration with g” sensor of the cell phone includes the gravitational acceleration of the Earth in the accelerometer readings. When the phone is tilted relative to the vertical direction, the acceleration readings on the 3 axes of the phone are the vector components of the gravitational acceleration vector. (The gravitational acceleration vector on the surface of the Earth is always pointing vertically down, with an approximate value of 9.81 m/s2.)
Demonstration Video: https://youtu.be/9PdVDBwTneA
Procedures
Part 1: Static Friction
- In the Phyphox app, open the “acceleration with g” sensor.
- Place the board on the floor. Rest the phone on top of the board with one edge of the phone parallel to the edge of the board. Start an acceleration with g measurement.
- Put soft padding on one side of the board (to catch the phone and stop the slope from skidding). Slowly lift the other side of the board until the phone starts to slide down. Stop the measurement.
- On the accelerometer readings, you should see the acceleration component that is parallel to the direction of the slope increase gradually before a small drop. (In the example screenshot below, the y axis was gradually increasing before a small drop at about 4 seconds mark.) Note down the time point and the acceleration immediately before the drop. This time point is the time point when the parallel component of gravity exceeds the maximum static friction.
- On the other graphs showing the other components of the gravitational acceleration vector, Note down the values of acceleration at the time when the parallel component of gravity exceeds the maximum static friction.
- Repeat the steps 2-5 above for a total of three times.
- Show that the vector sum of the components of the measured acceleration is indeed similar to the accepted value of gravitational acceleration on the surface of the Earth.
- Use the values of the components of acceleration that you read to calculate the tilt angle of the board at which the phone starts to slide down.
- Use the values of the components of acceleration that you read to calculate the coefficient of static friction between the back of your phone and the board. (Question: