Question

# The maximum frictional force that comes into play when a body just begins to slide over the surface of another body is known as:A) Dynamic frictionB) Rolling frictionC) Kinetic frictionD) Limiting friction

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Hint: Static friction is the frictional force which acts on objects which are at rest. Kinetic friction is the frictional force which acts on objects which are moving. The value of frictional force when static friction converts to kinetic friction is known as limiting friction.

Frictional force is the force which opposes the movement of an object. Whether the object is at rest or in motion, frictional force acts on it. There are many types of frictional forces like static friction, kinetic friction, rolling friction, fluid friction, etc.
Static friction refers to the frictional force which acts on objects which are not moving. This force opposes the movement of objects at rest. Limiting friction is defined as the maximum frictional force which acts on an object when it just begins to move. We have always wondered how cars are parked on sliding surfaces like hilly areas. It is due to the strong frictional force acting on the car which restricts the movement of the car. When a car is parked on a sliding surface, static friction acts on it. The minimum force required to make the car start moving is equal to the limiting friction. We can also experience static friction when we try to move heavy objects. It takes a little time before the heavy object starts moving when we push. It is because of the static frictional force acting on the heavy object at rest. Once the limiting friction is reached, the heavy object starts moving. At that particular moment when limiting friction is reached, the value of limiting friction is equal to the applied force. Mathematically, limiting friction is given by
$F=\mu N$
where
$F$ is the limiting friction
$\mu$ is the coefficient of limiting friction
$N$ is the normal force
Limiting friction is directly proportional to the mass of the object as well as the roughness of the surface in contact with the object.