Static Friction

The maximum frictional force present between any two objects when one object just tends to move or slip called static friction. Static friction is a kind of starting friction because an object just tends to start moving, it does not actually move. The object remains static (or stationary) in this case. We can demonstrate the static friction between a wooden block and a table top by performing an activity as follows : A wooden block (having a hook attached to its one side) is kept on the horizontal surface of a table. A spring balance is attached to the hook of wooden block (as shown in Figure 9). We pull the spring balance to the right side with a small force of our hand. This will exert a force on the wooden block. The wooden block, however, does not move because its motion is being opposed by the force of friction which acts in the opposite direction (to the left side). As we increase the pulling force applied to the wooden block (through spring balance), the friction also goes on increasing. But ultimately, when the applied force becomes a little more than the maximum frictional force, the wooden block just tends to move or slip on the surface of table. This means that the frictional force acting between the wooden block and table top has a maximum value beyond which it cannot increase. The force which we are exerting in making the wooden block just tend to move or slip is equal (but opposite) to the force of friction. In Figure 9 we can see that when the wooden block just tends to move or slip on the table top, the spring balance shows a reading of 5 N force (5 newtons force). This means that the magnitude of static friction between this wooden block and table top is of 5 newtons.

From the above discussion we conclude that the force required to overcome friction at the instant an object just tends to start moving from rest, is a measure of static friction. Static friction comes into play when we try to move a stationary object (which is at rest). Please note that in the case of static friction, the object is actually not moving or sliding over the other object, it only tends to move or slide.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

The maximum frictional force present between any two objects when one object just tends to move called __________________ .
A. Static friction	B. Rolling friction	C. Sliding friction	D. None of these .
Right Option : A
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Question : 2

Force of Friction which exists between the different layers or films of a liquid is known as _____________________ .
A. Fluid Friction	B. Sliding Friction	C. Rolling Friction	D. Lubricated friction
Right Option : A
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Question : 3

A force of 5 N is required to move an object from rest. The value of static friction (f) is :
A. 5 N	B. f > 5 N	C. f > 6 N	D. 10 N
Right Option : A
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