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While discussing about friction, a teacher gave a number of examples to explain the concept. Some of the examples where friction is useful in our day-to-day life as quoted by the teacher are given below : A. We are able to write because of friction between the tip of the pen and the paper. B. We are able to walk because of friction between our feet and the ground. C. A ball thrown vertically upwards comes back to us due to friction. D. We are able to stop a moving vehicle by applying brakes because of friction. The correct examples were

While discussing about friction, a teacher gave a number of examples to explain the concept. Some of the examples where friction is useful in our day-to-day life as quoted by the teacher are given below : A. We are able to write because of friction between the tip of the pen and the paper. B. We are able to walk because of friction between our feet and the ground. C. A ball thrown vertically upwards comes back to us due to friction. D. We are able to stop a moving vehicle by applying brakes because of friction. The correct examples were Correct Answer D, A and B

Concept:

  • Friction: The property of a surface that opposes the relative motion between two surfaces is called friction.
  • Friction opposes the relative motion between two surfaces. 
  • It is denoted by f and the SI unit of the frictional force is Newton (N).

  • Friction (f) = μ N, where μ is the coefficient of friction and N is the normal force

There are four types of friction:

Static friction:

  • It is defined as the frictional force that acts between the surfaces when they are at rest with respect to each other.
  • Example: Creating heat by rubbing both hands together.

Sliding friction:

  • It is defined as the resistance that is created between any two objects when they are sliding against each other.
  • Example: Sliding of the block across the floor.

Rolling friction:

  • It is defined as the force which resists the motion of a ball or wheel and is the weakest type of friction.
  • Example: Wheels of the moving vehicles.

Fluid friction:

  • It is defined as the friction that exists between the layers of the fluid when they are moving relative to each other.
  • Example: The flow of ink in pens.

  •  A ball thrown vertically upwards comes back to us due to gravity.

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