Balls Bonner

Unit Assessment

I. Purpose: Our purpose of this lab was to determine the kinetic coefficient of friction, to determine stopping distance and to determine maximum curve speed through lab procedures.

II. Procedure for Collecting Data:

1. Acquire a piece of rubber that is as similar to car tire material as possible and it should be around 7.5 centimeters square

2. Record mass of rubber, when necessary mass out the added weight

3. Connect rubber piece to spring scale

4. Place rubber and spring scale on asphalt

5. Lightly tug on spring scale to move rubber across asphalt and record the maximum value of force that can be read off of the scale right before the rubber shows movement this will be known as the static friction force

6. Repeat step five but instead of recording the value right before the rubber moves you will record the value as the rubber moves at a constant pace this will be known as the kinetic friction force

7. Add mass to the rubber (200 grams, 400 grams and 500 grams)

8. Repeat steps two through 6 for each of the added masses and record the data in a table

9. Graph data in two scatter plots: Static Friction force vs. Normal Force and Kinetic Friction Force vs. Normal Force

10. Find the mu by calculating the slope of the line of best fit. This mu will be the coefficient of friction

III. Procedure for Analyzing Data:

1. The mu will be calculated by averaging each coefficient of friction from all four graphs done by group members. Each individual mu will be found by calculating the slope of the line of best fit from each graph whether it is static or kinetic friction.

2. The average mu of kinetic friction will then be used to calculate the velocity through the formula distance equals velocity squared divided by two times mu times gravity. This is used to calculate stopping distance with given initial velocity.

3. You will then use the average static coefficient of friction to determine the maximum speed that you should drive when going around a curve. The formula used is centripetal force equals mass multiplied by centripetal acceleration.

IV. Results: see calculations and graphs attached

V. Conclusion:

Our conclusion that was found through calculating the coefficients of friction was that static friction will always be greater than kinetic friction. This is because it takes more force to get the rubber moving than to keep it moving at a constant speed.