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Consider the following statements: Polishing helps in increasing friction. Lubricating the machine helps in reducing friction. Usage of ball bearings is an effective way to reduce kinetic friction. Sand is spread over the tracks covered with snow to increase friction. Which of the above statements is correct.

Consider the following statements: Polishing helps in increasing friction. Lubricating the machine helps in reducing friction. Usage of ball bearings is an effective way to reduce kinetic friction. Sand is spread over the tracks covered with snow to increase friction. Which of the above statements is correct. Correct Answer 2) and 3) and 4) only

CONCEPT:

  • Frictional force: It is a type of contact force.
  • Contact forces: It arises when two bodies are in contact with some other object: solid or liquid
    • When two bodies are in contact mutual force arise due to newton's third law of motion.
    • The component of contact force normal to the surface is called normal reaction and the component parallel to the surface is called friction.
  • Static friction: It is the force of friction that balances the external force applied on the body and keeps the body at rest.
    • It opposes the impending motion of the body.
  • If fs is the static frictional force μs is the coefficient of static friction and N is the normal reaction force, the law of static friction may be written as:

⇒ fs ≤ μsN

The maximum value of static friction:

⇒ (fs)max = μsN

  • Kinetic friction: The frictional force that opposes the relative motion of two surfaces in contact.

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  • If fk is the kinetic friction, μk the coefficient of kinetic friction, and N is the normal reaction force, the law of kinetic friction may be written as:

⇒ fk = μkN

  • Rolling friction: When an object is rolled over the surface of another object an opposing force comes into action. This opposing force is called rolling friction.
    • The rolling body in contact with the plane gets slightly compressed and the motion relative to the plane is zero.
    • The net effect is that component of contact force parallel to the surface opposes the motion.

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​EXPLANATION:

  • Polishing helps in reducing friction. It makes the surface smoother and thereby reducing the friction.
  • Lubricants fill up the irregularities of the surface of the body. This smoothens the surface. So lubricating the machine helps in reducing kinetic friction.
  • Usage of ball bearings is an effective way to reduce rolling friction. Since the rolling friction between the ball bearings and the surface in contact is very small, power dissipation is reduced.
  • Sand is spread over the tracks covered with snow to increase friction. Driving becomes safer as the force of friction between the wheels of vehicles and the road increases.

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