Why is it difficult to move certain objects? What is the reason behind the motion of objects from a state of rest? We find that some force is opposing the change in the state of motion. This force is called static friction. In this article, we look at the definition, formula, laws, and examples of limiting friction.
What is static friction?
Static friction is the frictional force acting on objects at rest. It tries to oppose any force trying to move the object. It is a self-adjusting force. So, it will try and match the force applied to the object.
limiting friction Definition
We can define Limiting friction as the value of friction when a stationary object is just about to move. In other words, It is the minimum force required to make a stationary object move. It is the maximum value of friction for a given pair of materials.
Static friction is a self-adjusting force. It tries to match the external force applied to the body. When the value of force applied crosses the value of limiting friction, then the static friction gets converted to kinetic friction. After which the object begins to move. You can understand this by seeing the friction plot below.
When an object is in a state of rest, static friction acts on the object. But, after the limiting friction, you can see a drop in the value of frictional force. This is due to the fact that, when an object is in motion, the interlocking between the surfaces at the microscopic scale will be less. The value of kinetic friction is always lower as compared to kinetic friction.
The formula of limiting friction
limiting friction = μlimiting x normal force [ f = μlim x N ]
Where μlim is the coefficient of limiting friction. It is a constant that is unique to a pair of sliding materials. The higher the value of the limiting friction coefficient, the more difficult it is to move the object.
What are the examples of limiting friction?
- A car parked on a hill will not slide down. This is because the value of limiting friction is high enough to ensure that the car is in a state of rest. The limiting force of friction is directly proportional to the mass of the object.
- Pushing a heavy truck seems very difficult due to the high value of static friction
- When you push any object you encounter static friction for some time until the value of limiting friction is reached.
Is limiting friction static or kinetic?
Limiting friction is always static. It is the maximum value of static friction and comes into action when a body is at rest.
Why is kinetic friction less than limiting friction?
When an object is at rest, there will be maximum contact between the surfaces. Hence, the interlocking will be stronger as compared to when the object is in motion.
What are the laws limiting friction?
- It is always opposite to the direction of motion of the object
- At that moment, the value of the applied force is equal to limiting friction.
- It is a constant value
- It is directly proportional to the mass of the object
- It is directly proportional to the roughness of the surfaces
Is limiting friction a self-adjusting force?
Limiting friction value is not self-adjusting. It is a fixed value for a pair of materials. It may change depending on the nature of the sliding materials. But, the value of static friction is self-adjusting. The maximum value of static friction is called the limiting force of friction.
See also:
- Types of friction
- Advantages and disadvantages of friction
- Kinetic friction-Definition|formula|examples
- Coefficient of kinetic friction
- Coefficient of friction – Definition|formulae|Examples
- Sliding friction
- Examples of rolling friction
- Causes of friction
- Examples of static friction
- Examples of fluid friction
