PHYS 211
Friction Lab
Part A: Exploring Static and Kinetic Friction Forces
In this activity you will experimentally generate a Force vs Time graph while slowly
pulling on an object and identify the static and kinetic friction forces on the graph.
(1) Hook up a Vernier Force Sensor to your object. Slowly begin pulling on the
object with the force sensor while collecting force data until it slides along the
table. Identify the maximum static friction force and the kinetic friction force.
(2) Add some significant weight to your object and repeat the force measurement.
QUESTIONS:
1. Is the static friction force constant?
2. How does the magnitude of the maximum static friction force compare to the
kinetic friction force? Based on this observation, why would using anti-lock
brakes be more effective at stopping a car than simply stomping on the brakes
and skidding the tires?
3. How did the friction forces change when you added weight to the object? WHY
did they change (what affected the friction force)?
HINTS AND COMMENTS:
1. Note that the force sensor has a switch to change the range over which it
measures. You will likely need to lower range for this experiment.
2. When you first start to pull on the object, it should feel like it’s “stuck” to the
table. Once the object begins to move, try to slide it at a constant acceleration.
PART B: Finding the Coefficient of Friction, μs
In this activity you will determine the static coefficient of friction for your textbook and
another object placed on the book using “old school” techniques.
Place the object on your textbook. Keeping one edge of the book on the table, lift
up the other edge of the book until the object just barely begins to slide. Measure
the angle between the textbook and table. From this one measurement, determine
the static coefficient of friction for your book and the object.
QUESTIONS
1. What is the direction of the static friction force?
HINTS AND COMMENTS
1. You will need to figure out this analysis on paper, using the free-body-diagram
technique.