Consider an absolutely rigid flat bar of your choice, with a flat and relatively smooth top surface, of about 1.5 m – 2 m long, lying on a horizontal floor. Consider also a brick with flat and relatively smooth base bottom surface. With the bar resting on a horizontal ground surface, let the bottom surface of the brick rests on the flat horizontal top surface of the bar, close to one end; record the respective materials of the two surfaces in contact).Protocols I. From the floor:

1) Curve (block) the opposite end of the bar.

2) Now lift the other end of the bar with the brick from the floor, gradually up to the height where the block “just starts sliding” down the bar inclined.

3) Record the height of the bar edge with respect to the floor, so to determine the angle of the bar about the horizontal floor. This is the angle of repose for this system

4) Repeat steps 2), 3) and 4) three times with different loading, while keeping surfaces of contact unchanged. Compare yet the various 3 angles of repose.

5) Evaluate the coefficient of static friction between the brick and the bar, for each loading of step 4) above. How do they agree with each other? Explain briefly eventual discrepancies.

6) Find the average of the three coefficients obtained in 5) above. Does it agree with the value of coefficient of static friction obtained from literature?

II. For the coefficient of Kinetic Friction:

7) Now, position the bar at a convenient inclination likely to provide an easy sliding of the block down the incline (this angle must surely be greater than the above angle of repose). 

8) Place the object at a conveniently measured distance from the bottom end of the inclined

9) Set your chronometer at 00.00, and release the brick. Record the time as the brick “just arrives” at the bottom of the inclined 

10) Use the kinematic equation of uniformly accelerated motion to determine the acceleration of the brick in the conditions of step 9) above.

11) Evaluate the Coefficient of kinetic friction between your brick and bar, (with the use of the literature in 14) below.

12) Repeat steps 8), 9), 10) and 11) above and find the average of the three eventual coefficients. Does it agree with coefficient of kinetic friction obtained from literature? Literature Hints

13) For the two respective materials in contact you have recorded for your experiment, go to “google search” to look for their ranges of coefficients of static friction and coefficient of kinetic friction respectively.