What is Frictional Force? – Formula, Example, Types

What is Frictional Force?

The frictional force is a fundamental concept in physics that refers to the resistance encountered when two objects come into contact and attempt to move relative to each other. It is the force that opposes the motion or tendency of motion between the surfaces of two objects in contact. Frictional force arises due to the irregularities on the surfaces and the interaction between the molecules of the objects. 

Frictional force plays a significant role in our daily lives. Whether it’s walking, driving, or even writing, we constantly experience frictional forces. Understanding this force is crucial for various scientific and practical applications. 

Frictional Force Examples

To better understand the concept of frictional force, let’s consider a few examples: 

• When you try to push a heavy box across the floor, you encounter resistance. The frictional force opposes your applied force, making it harder to move the box. 
• When a car applies brakes to slow down, the frictional force between the brake pads and the wheels helps in reducing the car’s speed. 
• A pencil on a table stays in place due to the frictional force acting between the pencil and the table’s surface. 

These examples highlight the omnipresence of frictional force in our daily lives. 

Formula of Frictional Force

The mathematical expression for frictional force is given by the formula:

\(F_{frict} = \mu F_{norm}\)

Where,

• \(F_{frict}\) is the frictional force.
• \( \mu\) is the coefficient of friction, representing the interaction between the two surfaces.
• \(F_{norm}\) is the normal force, which is the force exerted perpendicular to the surfaces in contact.

The mathematical formula to calculate frictional force depends on the type of friction involved. There are two types of friction: static friction and kinetic friction. The formulas for these types differ: 

Static Friction: When objects are not moving relative to each other, static friction comes into play. The formula for static friction is: 

\(F_{s} \leq \mu _{s} F_{n}\)

where Fs represents the static frictional force, μs is the coefficient of static friction, and Fn is the normal force between the two objects. 

Kinetic Friction: When objects are in motion relative to each other, kinetic friction is present. The formula for kinetic friction is: 

\( F_{k} = \mu _{k} F_{n}\)

Here, Fk denotes the kinetic frictional force, μk is the coefficient of kinetic friction, and Fn represents the normal force. 

By knowing the coefficients of friction and the normal forces involved, you can calculate the frictional forces in various scenarios. 

Steps to Calculate Frictional Force

To determine the frictional force present in a given situation, follow these steps: 

1. Identify the type of friction involved, whether it is static or kinetic. 
2. Determine the coefficient of friction (μ) for the given surfaces. This information is often available in physics reference books or can be experimentally measured. 
3. Calculate the normal force (Fn) between the two objects. 
4. Substitute the obtained values of μ and Fn into the corresponding frictional force formula. 
5. Solve the equation to find the frictional force acting on the objects. 

By following these steps meticulously, you can accurately calculate the frictional force in various circumstances. 

Units of Frictional Force

The unit of measurement used for frictional force depends on the unit system employed. In most cases, the frictional force is measured in Newtons (N) in the International System of Units (SI). However, other units such as dyne or pound-force can also be used to express frictional force in different systems. 

Types of Frictional Force

Frictional force can be further categorized into different types based on the nature of the surfaces and the conditions under which it occurs. Let’s explore each of these types and their subtypes: 

Dry Friction

Dry friction, also known as Coulomb friction, is the most common type of friction that occurs between solid surfaces in contact. It can be further divided into two subtypes: 

1. Static Dry Friction: Static dry friction comes into play when an object is at rest and resists any attempt to set it in motion. It prevents the objects from sliding past each other. 
2. Kinetic Dry Friction: Kinetic dry friction occurs when the object is in motion relative to another surface. It opposes the motion and acts in the opposite direction. 

Dry friction is experienced in various everyday situations, such as when you try to walk on a rough surface or when gripping an object. 

Fluid Friction

Fluid friction, as the name suggests, refers to the friction experienced by objects moving through a fluid, such as air or water. It encompasses two significant subtypes: 

1. Viscous Friction: Viscous friction is encountered when an object moves through a highly viscous fluid, like honey or oil. It arises due to the internal friction within the fluid and opposes the motion of the object. 
2. Drag Force: Drag force, also known as air resistance or water resistance, is a type of fluid friction experienced by objects moving through air or water. It increases with the speed of the object and acts in the opposite direction. 

Fluid friction is prevalent in scenarios such as swimming, flying, or even the movement of vehicles through the air. 

Final Notes

The frictional force is a fundamental aspect of physics that influences almost every aspect of our lives. Its existence is crucial in maintaining stability, controlling motion, and enabling the functionality of countless objects and systems. By understanding the formulas, types, and examples of frictional force, we gain a deeper appreciation for the role it plays in the world around us. 

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FAQ’s

Q: What is frictional force? 

A: Frictional force is the resistance encountered when two objects come into contact and attempt to move relative to each other. It opposes the motion or tendency of motion between the surfaces of the objects. 

Q: What is the direction of frictional force? 

A: The direction of frictional force always acts opposite to the direction of the applied force or the motion of the object. It hinders the relative motion between the surfaces in contact. 

Q. What are the Types of Friction?

A. Friction manifests in various forms, and the primary types include:

1. Static Friction:
   • Definition: Static friction occurs when an object is at rest and resists the initiation of motion.
   • Example: Trying to push a heavy box that initially doesn’t move due to static friction.
2. Kinetic Friction:
   • Definition: Kinetic friction comes into play when an object is already in motion, opposing its movement.
   • Example: Sliding a book across a table encounters kinetic friction.
3. Fluid Friction:
   • Definition: Fluid friction occurs when an object moves through a fluid, be it a liquid or a gas.
   • Example: Feeling resistance while moving your hand through water.

Q. Give a Few Examples of Friction

A. The following are a few examples of Friction.

• Walking on the Ground
• Sliding a Box
• Braking in a Car
• Moving Furniture
• Writing with a Pencil

Q. What is Fluid Friction?

A. Fluid friction refers to the resistance encountered when an object moves through a fluid, which can be either a liquid or a gas. There are two main subtypes of fluid friction:

1. Lubricated Friction:
   • Definition: Lubricated friction occurs when a fluid, like oil or grease, is introduced between two surfaces to reduce friction.
   • Example: Oil lubricating the moving parts of a car engine.
2. Viscous Friction:
   • Definition: Viscous friction is the resistance to motion within a fluid itself.
   • Example: Feeling resistance when moving your hand through honey or syrup.

Q. What is Dry Friction?

A. Dry friction is the resistance between two solid surfaces in contact without the presence of any lubrication or liquid medium. It can be further classified into two subtypes:

1. Static Friction:
   • Definition: Static friction prevents an object from starting to move when a force is applied.
   • Example: Trying to push a heavy box that initially doesn’t budge due to static friction.
2. Kinetic Friction:
   • Definition: Kinetic friction comes into play once an object is already in motion, opposing its movement.
   • Example: Sliding a book across a table encounters kinetic friction.