Friction class 8 notes: Class 8 science ch 9 notes
| Textbook | Ncert |
| Class | Class 8 |
| Subject | Science |
| Chapter | Chapter 9 |
| Chapter Name | Friction |
| Medium | English |
Are you looking for Class 8 Science chapter 9 notes? Now you can download Friction class 8 notes pdf from here. In this chapter, we will study about frictional force, factors affecting friction, types of friction, methods to increase or reduce friction, and advantages & disadvantages of friction.
🌀 Friction :-
Friction is the force that opposes the relative motion or the tendency of such motion between two surfaces in contact. It acts on both the surfaces and depends on the nature (roughness or smoothness) of the surfaces in contact.
🔍 Types of Friction :-
🔒 Static Friction: The friction that comes into play when we try to move an object at rest, but it does not move. Example: Trying to push a heavy box lying on the floor, but it does not move.
⛸️ Sliding Friction: The friction that comes into play when an object slides over another. Example: A book sliding on a table.
🚗 Rolling Friction: When one body rolls over the surface of another body, the resistance to its motion is called rolling friction. Example: A toy car moving on the floor.
🐠 Fluid Friction: The friction experienced by objects moving through fluids (liquids or gases). Example: A fish swimming in water or an aeroplane flying in air.
🔸 Note: Fluid friction can be reduced by giving objects a streamlined shape.
⚙️ Cause of Friction :-
Friction is caused by the irregularities on the two surfaces in contact. Even those surfaces which appear very smooth have a large number of minute irregularities on them. Irregularities on the two surfaces lock into one another.
When we attempt to move any surface, we have to apply a force to overcome interlocking. This opposing force is what we call friction. Thus, the microscopic irregularities of the surfaces and the interlocking between them are the main causes of friction.
🔗 Interlocking :-
Irregularities on the two surfaces in contact may interlock with each other, which increases friction.
📊 Factors Affecting Friction :-
🪨 Roughness of the Surface: The rougher the surface, the greater the friction. Smooth surfaces have fewer irregularities, so friction is less.
⚗️ Nature of the Materials in Contact: Different materials have different levels of molecular attraction. For example, rubber on a road (tar) produces more friction, while ice on metal produces less friction.
💪 Normal Force / Pressure Applied: The greater the pressure applied on the surfaces, the more the friction. Friction increases with the force with which one object is pressed against another.
🔩 Interlocking of Irregularities: The more strongly the microscopic irregularities of two surfaces interlock, the greater the friction between them.
⚖️ Friction: A Necessary Evil :-
🔴 Why Friction is Harmful (Enemy):
❌ Reduces Efficiency of Machines: A part of the energy is lost as heat due to friction, which reduces the efficiency of machines.
❌ Causes Wear and Tear: The moving parts of machines rub against each other, leading to slow wear and damage over time.
❌ Leads to Energy Loss: The mechanical energy of moving objects is converted into heat energy due to friction, which is not useful for work.
❌ Limits Speed: Vehicles like buses, trains, airplanes, and rockets cannot increase their speed beyond a certain limit because friction opposes motion.
✔️ Why Friction is Useful (Friend):
✔️ Helps in Construction Work: Friction allows bricks to hold together and makes the construction of buildings possible.
✔️ Enables Writing: We are able to write on a blackboard or paper due to the friction between chalk and board, or pen and paper.
✔️ Helps Us Walk: Without friction between our feet and the ground, walking would be impossible—we would slip and fall.
✔️ Controls Vehicles: Friction between the tyres and the road helps vehicles stop when brakes are applied.
🔧 Increasing and Reducing Friction :-
➖ Ways to Reduce Friction:
🛢️ Using Lubricants: Substances like oil, grease, or graphite reduce friction between surfaces. They form a thin layer between surfaces to reduce direct contact.
🛞 Using Wheels or Rollers: Rolling is easier than sliding. That’s why we use wheels to reduce friction in moving objects.
✨ Making Surfaces Smooth: Polishing or smoothing a surface decreases irregularities and reduces friction.
🐬 Streamlined Shapes: Objects moving in air or water (like airplanes, or boats) are given streamlined shapes to reduce fluid friction.
➕ Ways to Increase Friction:
🪨 Making Surfaces Rough: Rough surfaces have more irregularities, increasing friction. For example, tyre treads increase friction to prevent slipping.
🧪 Choosing the Right Materials: Some materials, like rubber, create more friction than smooth materials like metal or plastic.
📥 Increasing the Weight or Force: Pressing two surfaces harder increases their contact and therefore increases friction.
🧂 Apply friction-enhancing substances: Like sand or grit on icy roads to avoid slipping.
🛢️ lubricants :-
The substances that are applied between two surfaces to reduce friction are called lubricants.
🌊 Ways to Reduce Fluid Friction :-
When objects move through fluids (like air or water), they lose energy due to fluid friction. To reduce this loss, objects are given a streamlined shape — a smooth, narrow shape that allows them to cut through the fluid easily.