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# Static Friction - JEE Important Topic

## Introduction to Static Friction

Last updated date: 20th Mar 2023
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As we already know, friction is a force that prevents the rolling or smooth motion of one object over another. This is beneficial sometimes when a person is walking on a road, this friction helps him/her to not fall or roll on the road and stay still and continue walking on it. This force can restrain the motion over solids or liquid surfaces or any material elements. This friction in physics is represented by the letter F.

This is categorized into many types such as dry friction, fluid friction, lubricant friction, skin friction and many more. Dry friction is friction which resists the motion of any two solid surfaces which are in contact.  Hence, based on whether the two surfaces or objects are staying still or in a motion, this is divided into other types which are namely Static Friction for the objects that are in rest and the Kinetic Friction for the moving objects.

In this article, we will get some insights about what is static force?, how static friction works? and its example.

## Definition and Examples

The static frictional force is a type of friction which assists a body to be at rest. This can also be understood when a person is trying to move a body which is at rest, he/she experiences a force when he is trying to move it. When he applies some force on the body to move it or lift it, the body remains at rest until the person overcomes its static friction.

And here, when the body begins to move, the kinetic friction force acts on it which controls the velocity of the object. The intensity of friction which keeps any two bodies in contact with very much grip on each other is measured with the help of a value called the coefficient of friction. This value is represented by the symbol μ and this value changes according to the nature of the surfaces we are dealing with. For static friction, $\mu$ is written as $\mu_s$ which is the coefficient of static friction.

Generally, there is a force that acts on every object which helps the object to be in equilibrium with the gravitational force and this is described as Normal force.  This force helps a body to stay on a surface instead of getting down on the land. This is represented by N.

There is a formula which helps us to figure out the relation between Static friction and the coefficient of static friction.

I.e., $F_{max}=\mu_s N$

where N is the normal force and Fmax is the maximum value of friction that a body can attain when it is being moved.

Let’s have a look at some of the examples where we confront this static friction in our daily lives.

1. A vehicle parked in a parking hall

2. A chair on the stage

3. Sticky notes on the wall

4. A book in a stack

5. Any objects placed on surfaces

We can find many more real-life applications of friction everywhere. If a parked car is experiencing friction, then it is the static one. If a moving car experiences friction, then it is about the kinetic frictional force.

## Laws of Static Friction

There are some static frictional laws which apply to a body that is at rest on a solid surface.

1. As in the above-discussed formula, $F_{max}=\mu_s N$, the maximum static frictional force is independent of the area of contact on the surface.

2. The maximum static friction is directly proportional to the normal force acting upon the body. If the Normal force increases, then the maximum force that an object can resist will also increase.

An important point to be noted is that the maximum value of static friction after which the object starts moving is called the Limiting friction. If and only if the force exerted on the body is greater than the limited friction, then it starts to be in motion.

## Laws of Limited Friction

These are the laws that are related to limited friction

1. The limited friction will act in the opposite direction of the force being exerted on the body.

2. The limited frictional force is proportional to the normal force of the bodies and it acts tangentially to them.

3. This depends on the type of material and the nature of surfaces which are in contact.

## Conclusion

Therefore, the static friction and how the static method works are discussed. Every example of static friction can be seen in our daily lives. The laws of static friction and limited friction are proven. If objects are at rest, there will be a connection between the body and the surface which helps to give rise to a much stronger static frictional force.

If a car is getting down from a sloped road, when the brake is applied, a force is being acted on it which eventually makes it stop.  This is due to static friction and the above-mentioned is a static force example that we have observed numerous times in our lives.

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## FAQs on Static Friction - JEE Important Topic

1. What is Stiction?

Stiction is the combination of two words static and friction which is widely used in the place of static frictional force. In simpler words, stiction could be defined as the total static friction that a person must overcome in order to create a motion in an object. Stiction is just adding all the static frictional forces that are spread to all the moving components of the system. This causes the change in velocity of the object which is also called overshoot in the position of the object.

2. How is static friction different from kinetic friction?

Static friction occurs only when the object is at rest with respect to the ground. Kinetic friction also called dynamic friction is a force that occurs when a body is in a relative motion with respect to the ground. Examples of static friction are a book resting on a table, a frame hung on the wall etc. Examples of kinetic friction are moving vehicles, objects sliding on the ground and many others. The magnitude of the coefficient of static friction is higher than the coefficient of kinetic friction.