# Static Friction

1. Jan 14, 2008

### Gear300

When an object, such as a wheel, rolls across a surface, static friction allows it to move. When taking into account rotational motion accompanied by translational motion across such a surface, what effect does static friction have on it other than allowing the object to move? Furthermore...what are the situations for which static friction can accelerate an object?

Last edited: Jan 14, 2008
2. Jan 14, 2008

When we look at rolling, we can say that the object (wheel/ball/whatever) is rotating around the point of contact with the floor, P. P is also moving forward with the translational speed of the rolling object. Static friction is what allows P to move forward rather than the object simply spinning in place.
Static friction accelerating an object? When we have a large block on a frictionless floor, and a smaller block on top of it. They are both moving together; static friction has not yet been overcome. We apply a force to the system to accelerate it until we break static friction. The sudden change in frictional force causes the large block to accelerate. But, I don't know whether this counts expressly as static friction accelerating the body.

3. Jan 14, 2008

### Gear300

I see...so static friction simply allows for the rotation to occur at point P. That implies that it does not take part in accelerating the object in any direction, right? Although, I heard somewhere that inclined planes are an exception to this; how so?

4. Jan 15, 2008