In this demonstration, the amount of force that it takes to overcome the force of static friction, and start an object moving, is compared with the weight of an object. Because the surface is parallel to the ground, the force pressing both surfaces together, is equal to the object's weight. The coefficient of static friction is shown to be directly proportional to the force pressing the objects together, for any area or surface type.
Please view the demonstration, and answer the following questions.
Things To Do
1. The coefficient of sliding friction, is the force required to overcome friction when the object is already moving. Do you think that coefficient is higher or lower than the force of static friction and why?
2. Is friction treated as a positive or negative force?
3. Is there anything like a frictionless surface?
The Angle of Repose
The Angle of Repose is the minimum angle required for an object to overcome the force of friction and begin sliding down hill under the force of gravity. In another sense, it is the maximum angle that a slope can be for unconsolidated material, before the force of gravity causes the material to slump.
In this demonstration, the Angle of Repose for a particular object and type of surface, is experimentally determined. After viewing the demonstration, please complete the Things To Do Questions.
Things To Do
1. Why is it necessary to do a vector resolution problem using the force of Static Friction, in order to theoretically determine the Angle of Repose?
2. What does a very low Angle of Repose tell you about the kind of surface at play?
3. What does it tell you about the Coefficient of Static Friction?