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What is Frictional Force, Its Types and Formulas?

The resistance to motion of an object moving relative to another is known as friction. It isn’t like gravity or electromagnetic force i.e. it isn’t a fundamental force. Instead, it is believed that it’s due to the electromagnetic attraction of charged particles in two adjacent surfaces. Here we will discuss that what is frictional force, its uses, advantages and types.

What is frictional force?

Friction or frictional force is defined as the force that prevents one solid item from moving across another. It always acts in the opposite direction to the direction of external force. Static friction, sliding friction, rolling friction and fluid friction are the four primary types of friction. Friction and normal force are proportional to the contacting surfaces and are independent of the contacting surface’s hardness. Sliding friction decreases as relative speeds increase, whereas fluid friction increases as relative speeds increase. Fluid friction is also affected by the viscosity of the fluid.

What is Frictional Force, Its Types and Formulas?

The force that prevents one solid item from slipping or rolling over another defines what is friction. Frictional forces, such as the traction required to walk without slipping, can be advantageous, but they also create significant resistance to motion. About 20% of an automobile’s engine power is used to overcome frictional forces in the moving parts. Although friction wastes energy but without friction, life cannot go on. As we even can’t walk without friction. In rainy days, the friction between our feet and road reduces that’s why we feel slippery.

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What is Frictional Force, Its Types and Formulas?

There are numerous exceptions to every basic rule about friction. For example, while two rough surfaces rubbing against one other can cause more friction, while very smoothly polished materials such as glass plates that have been thoroughly cleansed of all surface particles can actually attach extremely strongly to one other. Friction can also occur within the atoms of a solid material. When a solid block of metal is crushed, all of the atoms inside the material move, causing internal friction. There are no perfectly frictionless settings in nature: even in deep space, tiny particles of matter may interact, thus causing friction.

Coefficient of friction

The ratio of the frictional force preventing motion of two surfaces in contact to the normal force is known as the coefficient of friction. The Greek letter μ is generally used to represent it. μ = F/N, where F is the frictional force and N is the normal force. There is no units of friction coefficient i.e. the coefficient of friction is dimensionless since both F and N are measured in force units (newton).

Kinetic friction occurs when two solid objects move against each other. Friction is a fraction of the perpendicular force acting between two objects in this scenario (the fraction is determined by a number called the coefficient of friction). In general, the force is unaffected by the contact area and is unaffected by the speed at which the two objects are travelling. Friction exists in stationary objects as well. Static friction prevents things from moving and is often greater than the frictional force experienced when the same two things move relative to each other. Static friction prevents a box from sliding to the bottom of an incline.

One interesting fact about friction is that objects only fall when the line of center of gravity is out of the body, otherwise object will slip. Friction between solid parts is not the only source of friction; fluids can also cause friction (e.g., air and water). Fluid friction is the force of friction caused by air, water, and other fluids. When cars and planes travel at high speeds, the friction provided by the air molecules around plane, slows them down.

What is Frictional Force, Its Types and Formulas?

The friction of air causes drag, which opposes the vehicle’s motion. Ships and boats also work in the same way. Automobiles, ships, and aero planes are given a specific shape, termed a streamlined shape to reduce drag. When traveling through the air, an automobile with a streamlined body encounters the least amount of resistance. Even sea creatures like fish and shark have streamlined bodies, which makes it easier for them to move with great speeds in water. Frictional force can be reduced by using lubricants, polishing, ball bearings and streamlining. However, in some case, if more friction is required then friction can be increased by making the surfaces rough or by increasing the mass of the object that is moving.

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Types of friction

Friction is classified into 4 types

  • Static friction
  • Sliding friction
  • Rolling friction
  • Fluid friction

What is static friction?

What is Frictional Force, Its Types and Formulas?

Static friction is defined as the frictional force between two surfaces, which are in rest. This frictional force prevents them to move. 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 are moving. Heat by rubbing the hands, skiing against the snow and a book in rest on some table are examples of static friction. Static friction formula is given as

Fs = µη

Here Fs is static frictional force, µs is coefficient of static friction and η is the normal force. Static friction acts between surfaces at rest with respect to each other. The value of static friction varies between zero and the smallest force needed to start motion. This smallest force required to start motion, or to overcome static friction, is always greater than the force required to continue the motion, or to overcome kinetic friction.

What is Sliding Friction?

What is Frictional Force, Its Types and Formulas?

This frictional force is defined as the resistance created between two objects when they are sliding on each other. Sliding of blocks across floor or cards sliding against each other can be examples of sliding friction. Sliding friction formula is given by

Fs = µs. Fn

Here Fs is sliding frictional force, µs is coefficient of sliding friction and Fn is normal force.

What is Rolling Friction?

What is Frictional Force, Its Types and Formulas?

It is the weakest type of friction and is defined as the force that resists the motion of a wheel or a ball. Wheels of moving vehicles is an example of rolling friction. Rolling friction formula is given as

Fr = µr. Fn

Here Fr is the rolling frictional force, µr is the coefficient of rolling friction and Fn is the normal force. Phenomenon of rolling friction occurs when a wheel, ball or cylinder rolls freely over some surface, as in ball and roller bearings. The source of friction in rolling appears to be the dissipation of energy that is involved in deformation of the objects.

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What is Fluid Friction?

What is Frictional Force, Its Types and Formulas?

Friction is sometimes also known as viscosity. Fluid friction measures the resistance between moving layers of a fluid in liquids relative to each other. Honey has more fluid friction than water because more viscous fluids are thicker. Its examples include flow of ink in pen and swimming. Its formula is given as

F = µ A u / y

Here µ is coefficient of fluid friction, A is the area of top layer, u is the velocity of top layer and y is the separation between two layers.

Uses of friction

Friction is crucial in a variety of everyday processes. Friction converts some of the energy of motion into heat when two things rub together. This is why rubbing two sticks together causes a fire to start.

Friction is also to blame for the deterioration of bicycle gears and other mechanical components. To reduce friction between moving parts, lubricants, or liquids, are frequently utilized.

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