PHYSICS
LAB EXERCISE
COEFFICIENT OF FRICTION
NAMES: __________________________________
PURPOSE: To calculate the coefficient of friction between the tires of a toy truck and the surface of the floor.
MATERIALS: pull-back truck, meter stick, 2 stop watches
PROCEDURE:
1. Place a meter stick on the floor so that the zero end is on the line between two tiles. This is the Start Line.
2. Put the truck on the floor so that the front of the truck is on the Start Line.
3. Pull the truck back slowly until you hear a distinctive click. Measure the distance behind the Start Line and
record it in the Data Section.
4. Cleanly release the truck and measure the time that it takes the truck to return to the Start Line. Also measure
the time for the whole run of the truck. Record these times in the table in the data section.
5. Measure the distance from the Start Line to the point where the truck came to a stop. Record this distance in
the Data Section.
DATA:
Distance behind the Start Line = __________ cm
Distance from the Start Line to stopped truck = ________ cm
Time to return to the Start Line = ________ seconds
Total time = ________ seconds
CALCULATIONS:
1. What is the initial velocity of your truck? __________ cm/s (this is not a calculation – think about it)
2. Once the truck crosses the Start Line, the spring inside it has unwound and the truck begins to slow down.
Calculate the time it takes the truck to stop after it crosses the Start Line. Show all of your work here
and record your answer on the blank line provided.
Time to Stop = __________ seconds
3. You now have an initial velocity, a time and a distance that you can use to calculate the acceleration of your
truck. The equation you can use is...
d = vit + ½ at2
Use the distance behind the Start Line and the time for the truck to return to the Start Line to calculate
the acceleration of your truck. Show all of your work here and record your answer on the blank line
provided.
Acceleration = __________ m/s2
4. You can now use the same time and the acceleration of the truck to calculate the velocity of the truck as it
crossed the Start Line (this is the final velocity after it accelerated). Show all of your work here and
record your answer on the blank line provided. The equation you can use is...
vf = vi + at
vf = __________ m/s
5. When the truck crosses the Start Line, it is moving with the velocity you just calculated. Using this velocity as
the initial velocity, calculate the acceleration of the truck as it slows down. Use the equation below, the
distance from the Start Line to the stopped truck and the initial velocity from Calculation #4. Show all of
your work here and record your answer on the blank line provided.
vf2 = vi2 +2ad
Acceleration = __________ m/s2
6. Calculate the coefficient of friction (µ) between the tires and the surface of the floor. Show all work and
calculations below:
7. List three ways that the coefficient could be different.