Friction

Definition of Friction:

• Friction is a force that opposes the motion of one object over another. It acts between the two surfaces in contact.

Types of Friction:

1. Static Friction: The force of friction that acts between the two stationary surfaces.
2. Sliding (Kinetic) Friction: The force of friction that acts between two surfaces when one surface slides over another.
3. Rolling Friction: The friction experienced by a rolling object on a surface.

Comparison of Friction Types:

Static friction > Sliding friction > Rolling friction

Causes of Friction:

• Interlocking of surfaces due to presence of tiny hills and valleys.
• Force of adhesion between the atoms/molecules of two surfaces.

Factors Affecting Friction:

• Directly proportional to the force with which two surfaces are pressed together. For example, the weight of the body if it is placed on a horizontal surface.
• Depends on the nature of the surfaces in contact.
• Does not depend on the area of the surfaces in contact.

Advantages of Friction:

• Enables walking
• Enables movement of wheels .
• Helps in holding objects.
• Essential for braking.
• Necessary for writing with pens or chalk.

Disadvantages of Friction:

• Causes wear and tear.
• Generates heat and loss of energy.
• Reduces the efficiency of machines.

Ways to Increase Friction:

• Increasing roughness of the surface in contact.
  • Using treaded tires.
  • Grooved soles on shoes.
  • Rough and dry surfaces.

Ways to Reduce Friction:

• Polishing surfaces.
• Applying oil or grease, lubricants.
• Using ball bearings.
• Streamlining the shape of objects.
• Sprinkling soft powder.

Drag or Fluid Friction:

• The friction between a solid and a liquid or gas.
• Depends on the speed, shape, size of the object, and nature of the fluid.