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Which of the following is NOT true about Frictional force? A. Friction is the force which opposes the relative motion of two surfaces in contact. B. The force of friction that acts when a body is moving (sliding) on a surface is called sliding friction. C. Friction in machines wastes energy and also causes wear and tear. D. Rolling friction is much more than sliding friction, the use of ball bearings in a machine considerably reduces friction.

Which of the following is NOT true about Frictional force? A. Friction is the force which opposes the relative motion of two surfaces in contact. B. The force of friction that acts when a body is moving (sliding) on a surface is called sliding friction. C. Friction in machines wastes energy and also causes wear and tear. D. Rolling friction is much more than sliding friction, the use of ball bearings in a machine considerably reduces friction. Correct Answer D

CONCEPT:

  • Friction: The property of a surface that opposes the relative motion between two surfaces is called friction.

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Friction (f) = μ N

where μ is the coefficient of friction and N is the normal force

There are three types of friction:

  • Static friction: The friction that exists between an object at rest and a rough surface on which it is placed, such friction is termed as static friction.
    • The coefficient of friction due to this friction is called a static friction coefficient.
  • Kinetic friction/sliding friction: The friction between the two surfaces when there is a relative motion between the surfaces then it is called kinetic friction.
  • Rolling friction: When a block is rolling (usually a circular body like a ball, tire) on a surface then the friction acting is called rolling friction.

EXPLANATION:

  1. Friction opposes the relative motion between two surfaces. So the statement A is true.
  2. When the body is moving then the friction acting is called sliding friction. So statement B is true.
  3. Friction in machines wastes energy and also causes wear and tear. Statement C is also correct.
  4. In the case of rolling motion, there is no relative motion between the two contact surfaces. So there is no work done by the friction in a rolling motion. That's why the rolling friction is less than the sliding/kinetic friction. So statement D is not true.

Related Questions

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