Observations and results
Did the tape-only penny stack usually start sliding down the clipboard first when you slowly raised the clipboard, increasing the angle of the slope?
The majority of the time the stack of pennies that were only coated in tape (and not a strip of paper towel) should have started sliding down the clipboard before the other stack of pennies did as the clipboard was raised up by its clip. For example, out of 10 trials the tape-only penny stack may have started sliding before the paper towel-wrapped stack in all of the trials. The resistance for downward movement on the slope is called friction, and it depends on the component of gravity that is perpendicular to the slope as well as the surfaces of the object and the slope itself. Because there was a greater amount of friction between the two paper towel–coated surfaces rubbing against one another than there was between the paper towel–coated surface and the tape-coated surface, the penny stack with a paper towel strip on it had a greater amount of friction, or resistance to movement, when going down the slope. This greater amount of friction should have given the paper towel–coated stack a greater angle of repose compared with the tape-only stack.
More to explore
Friction Basics, from Rader's Physics4Kids.com
Landslide Types and Processes, from the U.S. Geological Survey
Fun, Science Activities for You and Your Family, from Science Buddies
Landslides: What Causes a Hill to Become Creep-y?, from Science Buddies
This activity brought to you in partnership with Science Buddies