|When two real surfaces are in contact, an attempt to move either body with respect to the other will results in tangential friction forces developing.|
|The static frictional force builds up to match the applied horizontal component of force until it reaches its maximum value, at which point motion starts and a kinetic friction force acts.|
The maximum value of the static friction force is shown here...|
where is the coefficient of static friction
|For static conditions, before the maximum friction force is generated...|
For dynamic conditions, the frictional force is invariant and equal to
where is the coefficient of kinetic friction.|
Note: The coefficient of friction depends on materials and surfaces roughness.
|When a force is applied to a body, the locations of the normal force changes.|
Moments can be taken about the point indicated by 0.|
For case (1)...
||For case (2)...|
||For case (3)...|
|The normal force moves to keep the object in rotational equilibrium. When the normal force is a an extreme point (corner) of an object, tipping is imminent. Note the magnitude and point of application of P affects the tipping point.|
|Sometimes the friction and normal forces are combined into a resultant force and a friction angle is utilized.|
The friction angle is the angle between the normal and resultant force.|
The maximum static friction angle is determined as shown here...