Static and dynamic friction

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 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

There are two types of frictional forces called static and dynamic friction (kinetic friction).

Static friction 

Static friction is a force that keeps an object stationary. Static friction occurs when people try to move a solid object on a surface without 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 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 force to the floor, the floor beneath our feet exert equal and opposite force which is why we are not slipping. This follows the third law of motion.

Static Friction Laws

1. The direction of static friction is always opposite to the direction in which an object or body tries to move
2. The coefficient of static friction is always higher than the coefficient of kinetic friction
3. The force of static friction adjusts on its own. It increases with an increase in the applied force. The force of static friction is greater than or equal to the applied force until the motion begins

Examples of Static Friction

• A vehicle stopped on a hill
• Clinging to things
• Pushing a large object that is stationary, such as a truck
• sticky notes 

Coefficient of static friction, μs = Limiting frictionNormal force

The coefficient of static friction usually ranges between 0 and 1. There is no friction between the two objects if it is close to zero. On the other hand, if it is close to one, the friction between the objects equals the normal force. Sometimes, the coefficient is more significant when the frictional force is stronger than the normal force.

Kinetic friction (dynamic 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.

Fk= μk N

Fk = force of kinetic friction

μk = coefficient of kinetic friction

N= normal force

Applications of kinetic friction 

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

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

Differences between static and dynamic friction

Conclusion

In this article, Static and dynamic friction, we learned about the frictional forces and their types. There are two types of friction in nature: kinetic friction and static friction. We have studied both types and learnt the difference between these two. Also, the application of friction is explained in this article. It is almost impossible to imagine how the world would be without the force of friction. We can never hold objects, or we can never drive uphill without the frictional force. Static friction is the force that acts to keep the object at rest. Kinetic friction is a retarding force that slows down the moving object. The value of static friction increases with the applied force to a limit. Thus, static friction acts when two bodies in contact are at rest concerning each other.