Static friction – Definition, Law, Formula and Examples

We feel harder when moving the shopping trolley initially than continuously moving the shopping trolley. The initial push is the toughest thing when you want to push the bed over the bedroom. Perhaps many people think that it is a psychological thing, but the reason for this issue is physics. The main reason is static friction. 

Generally, the reason is a force for making the motion of two things harder to flow by one side or the other side. The friction lies between a stable material and the floor on which it is placed.

Static Friction Definition

The force that obstructs a thing’s motion moving in the direction is known as static friction. When a couple of objects glide among each other, static friction takes place. Friction is all over the world. For example, While walking, our feet are in contact with the surface.

When walking, our backward foot movement applies a force on the surface, and the other foot goes forward. When exercising the static friction pressures on the surface, the surface on our feet also applies the same amount of pressure and opposite power. This is under control with one of the laws of motion.

If we need to escape moving on the sharp hill due to friction, we will be able to do that. We must remember that the friction is in the opposite direction of relative motion. This will help to decrease the velocity, and at last, it stops. 

Static Friction Examples

The static friction examples are defined below:

• Rock on the floor
• A vehicle rested on a hill
• Keeping onto objects
• Pushing bulky weights such as bus
• Sticky note
• Legs of the fringed gecko
• Eyeglasses on the nose
• Knot tying
• The things going in a luggage carousel
• You are standing but the escalator is moving
• Dirt adhering to ground
• Water drops on a glass
• Pen cap fixing onto a pen
• A shirt dropped on a hook
• Caps on our head
• Placing the wall clock
• Roof tiles
• Books placed on the top of a table
• The book is in a folder
• A truck rested on a slope

What is Static Friction Formula? 

The resistive force which places a body at rest is known as static friction. Static friction is between an object placed at rest and the downhill surface. 

Fs =μs*N

μs – static friction coefficient of and 

N – Normal force

By static friction formula, we learned that the normal force and static friction are directly proportional. When the object’s weight is high, the static friction is also high.

• It does not depend on the region of the surface.
• It acts across the sliding surface contrary to the movement direction.
• Static friction relies on the inconsistencies in the object surface and sliding surfaces. Static friction is caused because of the integration of these irregularities.

Static Friction Formula

The force which arrests the motion of the gliding materials is known as friction. We will see friction everywhere. The object is sliding, and the force acting on the sliding object is in the opposite direction. 

If we move down the walkway and suddenly stop, we will be able to stop due to the friction between our slippers and the floor. Friction might be with a motion or motionless object. So, it might be forceful and also static. In this concept, we will go through the static friction topic and formula, along with examples. Let us have a look at it.

Consider that a vehicle is at rest. We need to apply more strength to switch on the vehicle without utilizing the accelerator. It is because of static friction. Here the vehicle without motion is a force to go to clash with the frictional force. Static friction comes under the resistive force noticed in an object at rest. 

This can be written as Fs=μs×Fn.

Where Fn is the Normal force

           μs is the static friction Coefficient of static friction

           And Fs is the Static friction.

Let us look at a simple example. 

Q: 300 N force is acted on the carton, which is of 5kg placed static on the surface. If the friction coefficient is 0.3, calculate the static friction using the formula of Static Friction.

Ans: Let us write the given values 

Normal force, Fn=300N,

Friction coefficient μs=0.3,

By using the Static friction formula:

Fs=μs×Fn

=0.3×300N

= 90 N.

Hence, 90N is the static friction.

Static Friction Equation

We can calculate the static friction by using the formula.

Static Friction = Normal Force x coefficient of Static Friction.

i.e. Fs=μs×Fn

For instance, take the 200N as normal force and the friction as 0.3, 

Then we calculate the static friction in the following way. 

 Static friction = 200 x 0.3. 

Static friction = 60 N.

Static friction coefficient

Friction is an obstruction where a floor or thing meets when they are in motion over another. This happens in a couple of methods: the initial one is that Kinetic friction applies to a thing that glides on the ground. In contrast, static friction is another method that takes place when friction restricts the material from moving. The coefficient varies for all the sets of objects that touch one another, including an object that connects with itself. 

Now we have a glance at the formula of static friction coefficient.

Static friction force = (static friction coefficient) × (normal force)

i.e., Fs=μs×N

Fs is the static friction force, μs is the static friction coefficient, and N is the normal force.

The static friction coefficient is boundless; it doesn’t contain any value. This will be a variable quantity, which signifies the force path that doesn’t impact the substantial values. The static friction coefficient value relies on the things which cause friction. 

Generally, their values lie between 0 and 1, but they must be higher than 1. When the value is equal to 0, there doesn’t have friction among a pair of objects. Every object has minimum friction when two objects interact with each other. The normal force and frictional forces are equal when the value is 1.

It is a misapprehension that the static friction coefficient is finite to zero and one between values. The normal force is weaker than the frictional force when the value of more than 1. A normal force like silicon rubber will contain static coefficient friction very higher than one. 

Laws of Static Friction

The laws of static friction are defined below:

• The frictional force is inverse to the motion of the object, which is placed over the ground of a stable object substantially to the ground under the act of outward force.
• The friction is always in the path irrelevant to the grounds of contact among both objects.
• When the applied force is less when compared to the frictional force, it restricts the object’s movement. 
• At the beginning of the movement, the resultant outside applied force in the direction of movement is the same as the greatest frictional force, known as limiting force.
• The extent of the limiting friction and the normal force are proportional to each other.
• When the normal force is constant, limiting friction relies on the contact region for the situation.
• Limiting friction is based on the surface of the two objects of the contact regions and unevenness among the grounds.

Difference Between Static and Kinetic Friction 

Static Friction	Kinetic Friction
1) It is friction that exists between two or more objects that are not moving in relation to one another.	1) Kinetic friction is the friction that exists between two or more objects that are moving in relation to each other.
2) The magnitude of static friction is greater because its coefficient is greater.	2) The magnitude of kinetic friction is reduced due to the low value of its coefficient.
3) The equation for static friction is given by Fs = μs η	3) The equation for kinetic friction is given by Fk = μk η
4) Its value is not limited to zero.	4) Its value is never zero.
5) As an example, consider a pencil on the table.	5) As an example, move the pencil across the top of a table.

 The kinetic friction equation is as follows:  

force of Kinetic friction = (kinetic friction coefficient) (normal force)

Fk = μk η Where, Fk = force of kinetic friction

μk is the coefficient of kinetic friction.

eta (Greek letter) = normal force = η

Conclusion

It is necessary to understand the fundamentals of static friction and how it works in real life. Without static friction, we cannot move or the things cannot remain in a stable equilibrium. Static friction is the friction among a pair of things in touch at rest, which is essential in starting a system. 

In comparison, kinetic friction defines the required kinetic energy at the time of the function. Friction and lifespan of a thing are connected; it means that easy running systems are also without bearings. Static friction arises from sticking, slight chemical interaction between surfaces. And generally, friction is produced by each surface’s defaults engaging together and coincidentally.

Frequently Asked Questions (FAQs)

1.Define static friction.

The friction among a pair of objects or very basic objects which are at rest with one another is known as static friction. For instance, static friction can restrict a thing from breaking up a slope. And a force that keeps a thing at rest is called static friction. The static friction that happens when an individual tries to push a motionless object on the ground without even producing any relative motion between the object and the floor where the object is placed is called static friction.

2.What controls are required for static friction?

 The following set of points to call a system working under static friction: 

• The body given must be motionless and in contact with one another.
• There must be interlinking of inconsistencies in the contact region.
• The applied force must follow one of the bodies and attempt to move.
• Still, the body must be motionless compared to other floors on things in contact.