Class 8 Science Chapter 12 Notes- Friction Notes

In this post, we will discuss Class 8 Science Chapter 12 notes pdf Friction Notes. Class 8th science ch 12 notes help students in revision. Friction notes class 8, we will learn about. You can also download the Friction notes class 8 pdf for further study. NCERT notes for the Class 8 Science Chapter 12 are designed by our subject expert team.

In this Class 8th Science Ch 12 Notes pdf, we will learn about Friction.

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Class 8 Science Chapter 12 notes Overview

Recall experience

  • Have you seen a moving ball on the ground stopping itself after some time?
  • Why do we slip when we step on a banana peel?
  • Why the moving object slows down self after some time when no external force is applied to? The answer to such questions is friction.
  • If an object started moving, it would never stop if there were no friction.

Force of Friction

Friction is the force that resists motion when the surface of one object comes in contact with the surface of another.

Class 8 Science Chapter 12 Notes  A boy falls down when he steps on a
banana peel
A boy falls down when he steps on a
banana peel
  1. If you apply the force along the left, friction acts along the right.
  2. If you apply the force along the right, the friction acts along the left direction.
  3. In both cases, the force opposes the motion.
  4. The force of friction acts between the two surfaces

Types of Friction:

a. Static Friction: When a body is at rest, the force of friction acting on it is known as static friction. This force is always equal and opposite to the applied force on the object. The force which is working, when the body is just at the point of sliding on the surface is known as limiting friction.

b. Sliding friction: The frictional force which opposes the sliding motion between two surfaces which are in contact. Sliding friction is generally smaller than static friction.

c. Rolling Friction: The frictional force which is present between the two surfaces when one body rolls over the other body. The rolling frictional force is usually smaller than the sliding frictional force.

Factors affecting Friction

  • Friction depends on the nature of surfaces in contact.
  • For a given pair of surfaces, friction depends upon the state of smoothness or roughness of surfaces.
  • Friction is less for smooth surfaces.
  • Friction is more for rough surfaces.
  • Friction is independent of the area of contact.
  • Friction depends on how hard the two surfaces are pressed together.

Friction: A Necessary Evil

Friction has advantages so considered a friend but due also has some disadvantages,  then it is a foe. Depending on the situation, friction could be helpful or could be a problem. Therefore, it is a necessary evil.

Advantages of Friction:

  1. It is friction between pen and paper which allows us to write on paper.
  2. The frictional force between our feet and the ground allows our movements like standing, walking and running.
  3. The frictional force between the surface of the road and the tyres of our vehicles allows the vehicles to move on the road without slipping.
  4. Vehicles can not be started or stopped or turned to change the direction of motion without friction.
  5. A nail can not tie a knot on the wall without friction.

Disadvantages of Friction

  1. Due to friction, moving objects tend to stop or slow as their motion is opposed.
  2. Due to friction heat is generated leading to wastage of energy in machines.
  3. Friction is responsible for the wear and tear of moving parts of machinery, soles of shoes, and tyres on the road after some time.

Effects of Friction

  1. Friction generates heat.
  2. Friction is responsible for causing wear and tear in tyres. 
  3. Frictional force always opposes motion.

Increasing and Reducing Friction

In some situations, friction is undesirable and we want to minimise it. or in some situations, friction is desirable and we want to increase it.

Increasing Friction

  1. The soles of shoes are grooved because they provided the shoes with better grip and increase friction so we can move easily.
  2. We can increase friction by using brake pads in the brake system of bicycles and automobiles.
  3. Gymnasts apply some coarse substances on their hands to increase friction for better grip.

Reducing Friction

  1. Friction can be reduced by providing wheels, hence used in suitcases, and school bags of kids.
  2. The frictional force acting between the sliding surfaces of two objects can be reduced by making the surfaces in contact smooth by polishing them.
  3. Sliding friction between the moving parts of vehicles and machinery can be reduced by applying oil, grease, graphite or any other lubricant.
  4. We can reduce friction by changing sliding friction replaced by rolling friction by using rollers like ball bearings are used between the hub and the axles in the moving parts of machines and vehicles.

Fluid Friction

Air is very light and thin. Yet it exerts a frictional force on objects moving through it. Similarly, water and other liquids exert a force of friction when objects move through them.

The frictional force exerted by fluids is also called drag.

  • Fluid Friction on an object depends on its speed with respect to the fluid.
  • Fluid Friction also depends on the shape of the object and the nature of the fluid.
  • The common name of gases and liquids is fluids.
  • For flow in the water, an object has to overcome Fluid friction. In this process, they lose energy.

What we learn Class 8 Science Chapter 12 Notes Friction Notes

In Class 8th Science Ch 12 Notes pdf / Friction Notes

  • Friction opposes the relative motion between two surfaces in contact. It acts on both surfaces.
  • Friction depends on the nature of surfaces in contact.
  • For a given pair of surfaces, friction depends upon the state of smoothness of those surfaces.
  • Friction depends on how hard the two surfaces are pressed together.
  • Static friction comes into play when we try to move an object at rest.
  • Sliding friction comes into play when an object is sliding over another.
  • Sliding friction is smaller than static friction.
  • Friction is important for many of our activities.
  • Friction can be increased by making a surface rough.
  • The sole of the shoes and the tyres of the vehicle are treaded to increase friction.
  • Friction is sometimes undesirable.
  • Friction can be reduced by using lubricants.
  • When one body rolls over another body, rolling friction comes into play. Rolling friction is smaller than sliding friction.
  • In many machines, friction is reduced by using ball bearings.
  • Fluid friction can be minimised by giving suitable shapes to bodies moving in fluids.

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