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Friction is the force that resists the relative motion of material elements, solid surfaces, fluid layers from rolling or sliding against each other. Friction basically arises from the action of irregularities of the harder surface plowing across the softer one. There are four types of friction, namely,
- Static friction
- Sliding friction
- Rolling friction
- Fluid friction
Read More: Frictional Force
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Key Terms: Friction, Force, Static Friction, Rolling Friction, Sliding Friction, Fluid Friction
What is Friction?
[Click Here for Sample Questions]Friction is the resultant force that arises when two surfaces are sliding or rolling across one another. The resisting force that acts on an object when it is in motion is known as the force of friction. Friction is the force that reduces the velocity of an object as it works in the opposite direction to the general direction of the moving object.
The irregularity of the surface is directly proportional to the friction produced. Heat is produced due to friction which can be experienced by rubbing hands together quickly. In the following sections, we are going to discuss several types of friction.
Force of friction (F) = µn
The normal force is equal to the weight of the object which can be expressed as
F = µmg
Read More:
| Centripetal and Centrifugal Force | Derivation of Centripetal Acceleration | Coefficient of Static Friction |
| Aristotle Fallacy | Static Friction | Impending Motion |
Types of Friction
[Click Here for Sample Questions]There are 4 types of friction depending on the types of motion which are as follows:
- Static friction
- Sliding friction
- Rolling friction
- Fluid friction
Static Friction
[Click Here for Sample Questions]When two static surfaces are at rest with each other, the friction that acts between them is known as static friction. When a limited amount of force is applied to the body, the amount of static force is equal to the opposite direction. Sometimes the static friction reaches the saturation point when the force is increased.
Examples of Static Friction
- Static friction is created between your shoe and the road while hiking in the woods
- Heat is produced as a result of static friction created by rubbing the hands together
- A table lamp on the table
- Skiing on the ice
- Using paint rollers to paint the walls
Coefficient of Static Friction
The value of static friction ranges from zero to the minimum force required to put a body on the motion. The force required to overcome kinetic friction or to continue motion is always less than or equal to the minimum force to start motion or to control static friction. It is represented as:
Fsmax = µs η and Fs ≤ µs η
Where,
Fsmax = maximum static friction force
η = normal force
Fs = static friction force
µs = coefficient of static friction
Read More:
| Friction Force Formula | Impulse Formula | Centripetal Force Formula |
| Newton’s Second law of motion formula | Static Friction Formula | Difference between Force and Momentum |
Sliding Friction
[Click Here for Sample Questions]When a moving body is sliding over a surface, the force acting on it is sliding friction. It is easier to slide furniture after you start moving it than to move the furniture initially because static friction is stronger than sliding friction.
Examples of Sliding Friction
- The use of the brake of the bikes retards the wheels by creating sliding.
- Friction between bike rims and brake pads.
- Sliding of furniture/block across the floor.
- Two cards sliding against each other.
- Speedy car.
- Opening of a sliding window/door.
Coefficient of Sliding Friction
Formula for coefficient of sliding friction is given by,
Fs = µs . Fn
Where,
FS = force of sliding friction
µs = coefficient of sliding friction
Fn = normal force
Rolling Friction
[Click Here for Sample Questions]Rolling Friction is the weakest type of friction and provides less friction between the surfaces. Because of the weak nature of rolling friction; bicycles, cars, rollercoasters, skates, etc use wheels. The loss of energy through the twisting of the object is the main source of friction.
Examples of Rolling Friction
- Wheels of vehicles in motion
- Rolling of log on the ground
Coefficient of Rolling Friction
Formula for coefficient of Rolling friction is given by,
Fs = µr . Fn
Where,
µr = coefficient of rolling friction
Fs = force of rolling friction
Fn = normal force
Read More:
| Acceleration Inclined Plane | Difference between Momentum and Inertia | Force and Acceleration |
| Interaction of Forces | Laws of Friction | Mass and Momentum |
Fluid Friction
[Click Here for Sample Questions]Fluid friction is the kind of friction that is exerted by the fluid on the object that is moving through a fluid.
Examples of Fluid Friction
- Fluid friction is experienced by a swimmer in water when he/she is swimming.
- The flow of ink in pens
- Opening hands in water
Things to Remember based on Types of Friction
- Friction is the force that resists two bodies or substances that are touching from moving against each other smoothly.
- The coefficient of rolling friction is 100-1000 times less than that of the coefficient of sliding friction which is practically realized by the use of wheels in the place of the sled.
- The value of the coefficient of friction = FN. where, F = frictional force, N = normal force
- Some examples of friction are- ignition of matches, motions of a piston in a cylinder, writing on books and boards.
- The coefficient of friction is constant. It is represented by the ratio between load (L) and friction (F). both friction and load are measured in newtons or pounds.
- The coefficient of static friction is Fsmax = µsη and Fs ≤ µsη
- The coefficient of sliding friction is Fs =µs . Fn
- The coefficient of rolling friction is Fs = µr. Fn
- Fluid friction is experienced by a swimmer in water when he/she is swimming
Check out PYQ on Friction:
Sample Questions based on Types of Friction
Ques: If the frictional force of an object is 80N and the normal force is 50N. What is the coefficient of friction? (2 marks)
Ans: Given, F = 80N and N= 50N
Coefficient of friction (µ) = FN
= 8050
= 1.6 N
Ques: A horizontal force of 15N pushes a 5 kg box on the horizontal table, will the box move if the coefficient of the fraction is 0.4? (2 marks)
Ans: The weight of the box is 5g whereas the mass is 5 kg. the vertical forces are in equilibrium. therefore, the maximum possible friction is the pushing force, 15N is less than this which is why it will not be able to overcome the friction. The box is not expected to move.
Ques: An object with a 10kg mass is placed on a smooth surface. 15N is the static friction between the two surfaces. What is the coefficient of static friction? (2 marks)
Ans: given, m= 10kg, F = 30N
Normal force (N) = mg
So, N = 10 * 9.81 = 98.1N
Coeffient for static friction (µ) = FN
µ = 3098.1
µ = 0.305
Ques: On a surface, a block of mass M= 10kg is inclined at angle ? which is 45?. The coefficient of static friction (µs) between the surface and the block is 0.5. (i) what is the minimum force required to avoid slipping? (ii) what is the maximum force required to prevent slipping? (3 marks)
Ans: the minimum force to prevent slipping = the minimum force required to prevent the block from sliding down the incline
Fmin = 10 g sin (45°) – 10 g cos (45°) * 0.5
The maximum force required to prevent the block from slipping = the maximum force required without causing the block to slide up the incline.
Fmax = 10 g sin (45°) + 10 g cos (45°) * 0.5
Fmin = 34.65N, Fmax = 103.94 N
Ques: What is friction? Name its types. (3 marks)
Ans: When two surfaces are sliding or rolling across one another, the force between the two surfaces is known as friction. The resisting force that acts on an object when it is in motion is known as the force of friction. Friction is the force that reduces the velocity of an object as it works in the opposite direction to the general direction of the moving object.
There are four main types of friction:
- Static friction
- Sliding friction
- Rolling friction
- Fluid friction
Ques: What is sliding friction? Write few examples of sliding friction. (4 marks)
Ans: When a moving body is sliding over a surface, the force acting on it is sliding friction. It is easier to slide furniture after you start moving it than to move the furniture initially because static friction is stronger than sliding friction.
Examples of sliding friction are:
- The use of the brake of the bikes retards the wheels by creating sliding friction between bike rims and brake pads.
- Sliding of furniture/block across the floor
- Two cards sliding against each other
- Speedy car
- Opening of a sliding window/door
Ques: What is meant by static friction? Write few examples of it. (4 marks)
Ans: When two static surfaces are at rest with each other, the friction that acts between them is known as static friction. When a limited amount of force is applied to the body, the amount of static force is equal to the opposite direction. Sometimes the static friction reaches the saturation point when the force is increased.
Examples of Static Friction:
- Static friction is created between your shoe and the road while hiking in the woods
- Heat is produced as a result of static friction created by rubbing the hands together
- A table lamp on the table
- Skiing on the ice
- Using paint rollers to paint the walls
Ques: A block of mass 10 kg is placed on a long trolley. The coefficient of the friction between the block and trolley is 0.2 and the trolley accelerates from rest with 0.5 m/s2 for 20 s. Then find the friction force. (3 marks)
Ans: Given, the mass of the block m = 10 kg
Acceleration of the trolley a =
According to Newton’s second law of motion, the force on the block by the motion of the trolley is given by the relation:
F = ma
10 x 0.5 = 5 N
Ques: Name the factors on which the frictional force exerted by a fluid on an object that is moving through it depends. (3 marks)
Ans: The factors on which the frictional force exerted by a fluid on an object that is moving through it depends, are as follows:
- The shape and weight of the object that is moving through the liquid.
- The nature or viscosity of the liquid.
- The speed with which the given object is moving.
Ques: State the dependency of the frictional force on the viscosity of the liquid. (3 marks)
Ans: Viscosity refers simply to the degree of thickness of the liquid. The more the viscosity thicker is the liquid more friction will be offered by the liquid to an object moving through it. Therefore, more the viscosity more the friction of liquid.
Ques: What is meant by rolling friction and write some examples. (3 marks)
Ans: It is the weakest type of friction that resists the motion of an object rolling over a surface. Because of the weak nature of rolling friction; bicycles, cars, rollercoasters, skates, etc use wheels. The loss of energy through the twisting of the object is the main source of friction.
Examples of Rolling Friction:
- Wheels of vehicles in motion
- Rolling of log on the ground
Ques: Frictional force always acts in the opposite direction to the direction of the motion of a body. Explain. (3 marks)
Ans: Frictional force always acts in the opposite direction to the direction of the motion of a body as friction is a reaction force that occurs due to the irregularities on the surfaces in contact, therefore it opposes the relative motion between two surfaces so that the body can be kept at rest. And friction is zero when the body is at rest.
Read More:
| Impulse Units | Newton’s Second Law of Motion | Newton’s Third Law of Motion |
| Inertia | Banking of Roads | Pseudo Force |
| Tension Force | Kinetic Friction | Motion in Physics |
Class 11 Physics Guides:
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