What is Frictional Force?

Frictional Force is the opposing force when two surfaces come in contact with each other to move either in the same direction or in opposite directions. As friction is a force that opposes or resisted the motion of an object that comes in contact and slide against each other. Hence, the frictional force is a Contact Force. Friction is a force that always opposes motion. The frictional forces are majorly affected by the texture of the surface of the objects that came in contact with each other and the amount of force exerted on them. Frictional Forces are classified into four different types, they are rolling, sliding, static and kinetic friction. Another important type of friction is Fluid Friction.

Frictional Force 

The frictional force is the force created when two surfaces come into touch with each other and slide against each other. 

These forces are mostly influenced by the surface roughness and the amount of force required when they are combined. The volume of frictional force is affected by the angle and position of the object. The forces of attraction are the primary cause of friction between objects. 

The frictional force between two surfaces always acts as opposes to the applied force, as shown in the figure above. The surface’s texture and the amount of force pushing them together have a big impact on the frictional force. The position and angle of the object have an impact on the friction force. The force of friction is equal to the mass of the thing when it is flat against another object. When we push an object up against the surface of another object, the frictional force increases and exceeds the weight of the pushed object.

Frictional Force Formula

The maximum frictional force applied on an object by a surface can be easily calculated by the following formula:

F_frict = µ × F_norm

where,

• µ is the coefficient of friction, and 
• F_norm refers to the normal force acting upon the said object, given as F = mg (where m is the mass and g is the acceleration due to gravity).

Unit of Frictional Force

• The unit of frictional force is kg.m/s² or Newton (N).
• The dimensional formula of frictional force is [M L T^-2].

Factors influencing Frictional Force

The magnitude of the frictional force depends on the following factors listed below:

• Surface textures and the amount of force pushing them together have a major impact on these forces.
• The amount of frictional force is affected by the position and the angle made by the object.
• The frictional force will be equal to the weight of the object if it is put flat against another object.
• The frictional force will increase and exceed the weight of the thing if an object is pushed up against the surface.

However, the frictional force between two surfaces is independent of the actual area of contact.

Types of Frictional Forces

The following are the two major types of frictional forces, based on the type of material in contact, that are:

Dry Friction

When two solid bodies come into contact, both when they are moving (kinetic friction) and when they are not, there is a reaction known as Dry friction (static friction). 

The normal force applied between the solid bodies determines how much friction there is, both in static and kinetic terms. Different coefficients of friction are used to represent the interaction of various materials. Hence, this implies that for a given normal force between two substances, certain substances have a stronger resistance to movement than others.

Based on the type of motion between the two objects, the frictional force may be classified as:

Static Frictional Force – Static friction is the amount of resistance that exists between an object and the surface it is resting on. The basic condition for moving an object that is resting on a surface involves applying a force that is greater than the frictional force generated by the surface. Another name for it is limiting frictional force. Static friction includes things like walking, rock climbing, and other activities.

Kinetic Frictional Force – When the box is sliding, kinetic friction develops beyond the point of coming motion. When there is kinetic friction, the normal force between the box and the surface multiplied by the kinetic coefficient of friction will equal the amount of friction force opposing motion. Although it also rests on the two objects in contact, the kinetic coefficient of friction is nearly always less than the static coefficient.

Rolling Frictional Force – Rolling friction is defined as the resistance created when one body is forced to roll across the surface of another. In comparison to kinetic friction, it is considerably less. Some of the applications where rolling friction can be easily seen include roller skates, ball bearings, etc.

Sliding Frictional Force – When one object is dragged across the surface of another, sliding friction results. Compared to static friction, it is weaker. Examples of sliding friction include dragging a block that is kept on the table, writing, playing on a slide, etc.

Fluid Friction 

A substance that can flow and can adopt the shape of the container in which it is kept is called a fluid. Fluid friction is the term for the resistance that a liquid or gas offers to a moving object. Hence, in simple words, the frictional force exerted by fluids is called the fluid friction.

The air resistance force or drag force is the term used to describe the frictional force produced by the air. Fluid friction makes it challenging to walk through a pool of water in the middle of a storm.

Examples of Frictional Force

Here are some different real-life examples of when we experience different types of frictional force, that are:

• Sliding a Sled – Sliding a sled over an icy surface is a good example of Sliding friction. The amount of friction between an object and the surface is reduced by the ice that has been deposited on the land or ground. The lack of friction on the surface makes objects on it easily slide and slid.
• Walking – Only when there is a force of friction between the ground and the feet can one walk. Since friction is a contact force, it exists between the points of the intersection. It helps in creating a solid connection between the foot and the ground. To continue, you must have solid contact. Because the force exerted on the ground is equal to and opposing the force of friction created by the ground, Newton’s third law of motion is also in play in this situation.
• Climbing – A force that tends to resist the climber’s ability to move on the rock can be felt when they do. Frictional force is the term given to this force. Rock climbing depends on friction to create a secure hold between the climber’s feet or hands and the rock’s surface. It helps climb the rock and keeps the climber’s hands and feet from slipping.
• Rubbing Hands – Sliding friction is illustrated by rubbing hands together. A force that opposes this motion of the hands is activated when they brush against one another. Frictional force is the force resisting motion that is exerted in a direction that is counter to the direction that the hands are moving, and it is what creates heat energy.

FAQs on Frictional Force

Question 1: Define Frictional Force.

Answer:

The frictional force is the force created when two surfaces come into touch with each other and slide against each other. 

Question 2: Which factors influence Frictional Force?

Answer:

The two important factors that influence the friction force the most are:

• Nature of the two surfaces in contact, and
• Nature of the force that are acting on these surfaces.

Question 3: How to calculate Frictional Force?

Answer:

The frictional force can be calculated by using the following formula:

F_frict = µ × F_norm

where,

• µ is the coefficient of friction, and 
• F_norm refers to the normal force acting upon the said object, given as F = mg (where m is the mass and g is the acceleration due to gravity).

Question 4: What is the unit of frictional force?

Answer:

The unit of frictional force in SI unit is kg.m/s² or Newton (N).

Question 5: Explain How Lubricant decreases Frictional Force between the objects?

Answer:

The lubricants cover the surface imperfections where the contact is made. Thus, friction is decreased when moving objects make touch with a lubricant.

Question 6: Give two examples of Frictional Force.

Answer:

Following are the two examples of frictional force:

• Only when there is a force of friction between the ground and the feet can one walk. Since friction is a contact force, it exists between the points of the intersection. It helps in creating a solid connection between the foot and the ground. 
• A force that tends to resist the climber’s ability to move on the rock can be felt when they do. Frictional force is the term given to this force.

Question 7: How the maximum of Static Friction is calculated?

Answer:

The maximum force of static friction is equal to the coefficient of static friction times the normal force on an object.

Question 8: What is the Work Done by Frictional Force?

Answer:

The work done by frictional force is always negative.