AP Physics 1 2.7: Static Friction

3 points
Note: In order to earn full credit for part (b), all terms (variables) must be indicated in the diagram and/or procedure of part (a).
For using Newton's second law (or reasoning in terms of zero net force) in one dimension, parallel to the board's surface, either explicitly or implicitly
For using Newton's second law (or reasoning in terms of zero net force) in one dimension, perpendicular to the board's surface, either explicitly or implicitly
Note: Replacing the normal force with m g is "implicit" use of Newton's second law in the perpendicular direction for a horizontal surface. For a tilted surface, the appropriate trigonometric term should be included.
For a correct derived expression of the coefficient of static friction in terms of quantities indicated in part (a)

1 point 1 point 1 point 1 point 1 point 1 point
Question 2

2 points
Correct answer: "The static and kinetic coefficients are not equal."
Reasoning cannot earn credit if the incorrect selection is made.
For identifying group 5's results as outliers, or indicating the presence of an outlier For a conclusion that coefficients are not the same, justified by either removing the outlier or noting the coefficients are different for each group

1 point
For a valid argument that indicates the coefficient of static friction is a property of the two surfaces, and is consistent with the selected answer

Example 1: Selects "Remain the same"
Referring to the equation in part (b), coefficient does not depend on mass.
Example 2: Selects "Remain the same"
The coefficient depends on the nature of the surfaces involved, not the masses or normal force of the objects involved.
Example 3: Selects "Decrease"
The increased normal force will cause smoothing of the surfaces, decreasing the coefficient of friction.
Example 4: Selects "Increase"
The increased normal force will cause the surfaces to become gouged, increasing the coefficient of friction.