Static and kinetic friction

Introduction 

Friction is a force that resists relative motion at the contact between bodies, as well as within bodies, also in the case of fluids. Leonardo da Vinci was the first to propose the concept of frictional force. The qualities of the surfaces, their surroundings, surface texture, the existence of the lubricant, and other factors all influence the amount of the coefficient of friction.

Scientists began putting together the principles controlling friction in the 1400s, but due to the complexity of the interactions, defining the force of friction in various conditions often requires tests and cannot be deduced only from equations or laws.

Types of friction

Static friction and kinetic friction are the two basic types of friction. Static friction occurs when two surfaces are not moving relative to one another, whereas kinetic friction occurs when two things move. Friction, often known as viscosity, is the resistance between moving layers of fluid in liquids. Honey has more fluid friction than water because thicker fluids are more viscous.

Friction can also occur within the atoms of a solid material. When a solid block of metal is crushed, for example, all of the molecules inside the material shift, causing internal friction. There are no frictionless settings in nature; even in outer space, microscopic matter particles can interact and cause friction.

Static friction 

Static friction is a force that keeps an object stationary. Static friction is the friction that occurs when people try and move a solid object on a surface without actually producing any relative motion between the body and its surface.

It’s regarded as the frictional force that keeps the applied force balanced for the length of the body’s static state.

When we walk, the backward motion of our feet puts pressure on the surface as the other foot moves forward. Furthermore, when we apply this friction force to the floor, the floor beneath our feet exert equal and opposite force. This is following one of the laws of motion.

The static frictional force is a self-regulating force, which will always be equal to and opposite to the applied force.

Static Friction Laws:

Two laws govern static friction:

First law: The greatest static friction force is independent of the contact area.

Second law: The maximum static friction force is proportional to the normal force, meaning that as the normal force grows, so does the maximum external force that the item can withstand without moving.

Examples of Static Friction :

• The ground is covered in stone.
• A vehicle stopped on a hill
• clinging to things
• Pushing a large object, such as a truck
• sticky notes 

Limiting Friction

 When an object is going to slide over the surface of another object, the highest degree of static friction comes into play. The body begins to move when an external force is applied that is greater than the limiting friction.

Static friction cannot be evaluated until the motion has begun. Kinetic friction is a new sort of friction that comes into play.

Limiting Friction Laws:

• The direction of limiting frictional force is always the opposite of the motion direction.
• Friction is reduced by operating tangentially on the two surfaces that are contacting.
• The usual reaction between the two surfaces determines the size of limiting friction.
• The material, the nature of the contacting surfaces, and their symmetry all influence the limiting friction.
• The degree of limiting friction is independent of the form or size of the surfaces as long as the normal reaction is the same.

Kinetic Friction

A force that acts between sliding surfaces is referred to as kinetic friction. A body moving on the surface is subjected to a force that opposes its progress. The size of the force will be determined by the kinetic friction coefficient between the two materials.

Friction is the force that prevents a sliding object from moving. Everything has kinetic friction, which interferes with the motion of two or more objects. The force works in the opposite direction of the object’s desire to slide. When a car has to stop, we use brakes, which is where the friction comes into play. When walking and wanting to come to a complete stop, friction is once again to thank. When we have to halt in the middle of a puddle, however, things get more difficult because friction is reduced and cannot help very much.

The kinetic friction equation can be written as

Fk= μk N

Fk = force of kinetic friction

μk = coefficient of kinetic friction

N= normal force

Kinetic Friction Laws:

Kinetic friction is governed by four laws:

1. The force of kinetic friction (Fk) is proportional to the normal response (N) between two surfaces in contact according to the first law, where μk is a constant known as the kinetic friction coefficient.
2. The force of kinetic friction is independent of the form and apparent size of the surfaces in contact, according to the second law.
3.  It is determined by the nature and material of the in-contact surface.
4. It is unaffected by the velocity of the item in contact as long as the relative velocity between the object and the surface is not excessively high.

Applications of kinetic friction 

The points below provide some real-world examples of kinetic friction.

• Kinetic friction is very useful in everyday life like it is used to stop a car or bus. If there is no friction then moving objects will never stop. 
• In the machines friction also causes wear and tear, to prevent this,  oil is used as a lubricant in machine parts.

Conclusion 

It would be impossible to live in a world without friction. Friction is vital in our environment because it influences everything that moves. Friction acts in the opposite way when an object moves, slips, or slides on one side.