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To stop a moving object, a force must act in the opposite direction to the direction of motion. For instance, if you push your book across your desk, the book will move. The force of the push moves the book. As the book slides across the desk, it slows down and stops moving. The force that opposes the motion of an object is called friction.



Friction is the force that opposes the motion of an object. Friction can slow down or stops any moving objects.


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What effect does friction force have on motion?

  1. It opposes the motion of all objects.
  2. It slows down any moving objects.
  3. It counteracts the acceleration of an object.
  4. It prevents surfaces from sliding against each other.
  5. It causes objects to accelerate.



Friction plays a vital role in our daily life. Without friction we are handicap.

  1. It prevents slipping while walking.
  2. It stops cars from moving.
  3. We cannot fix nail in the wood or wall if there is no friction. It is friction which holds the nail.
  4. A horse cannot pull a cart unless friction furnishes him a secure Foothold.



Despite the fact that the friction is very important in our daily life, it also has some disadvantages like:

  1. The main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy.
  2. Due to friction we have to exert more power in machines.
  3. It opposes the motion.
  4. Due to friction, noise is also produced in machines.
  5. Due to friction, engines of automobiles consume more fuel which is a money loss.



There are a number of methods to reduce friction in which some are discussed here.

  1. Use of Lubricants

The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity.


  1. Use of Grease

Proper greasing between the sliding parts of machine reduces the friction.


  1. Use of Ball

Bearing In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings.


  1. Design Modification

Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction.


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Strategies & Activities

Step: Teacher revises the previous topic

Step 2: Teacher introduces the new topic.

Step3: Teacher endeavors to explain all the points to the pupils thoroughly.

Step 4: Teacher welcomes pupils’ questions.

Step 5: Teacher evaluates the pupils.


Assessment & Evaluation

  1. Define friction;
  2. State two instance of the application of friction in daily activities;
  3. Mention two advantages and disadvantages each of friction.


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