Chapter 12 Friction Class 8 Notes | EduRev

Science - Short Notes for Class 8th

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Class 8 : Chapter 12 Friction Class 8 Notes | EduRev

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Chapter 12 – Friction 
Frictional Force – The opposing force exerted between two surfaces in contact is called force of friction. It is 
caused by irregularities in the surface.  
Frictional tries to stop a moving object i.e. it works in the direction of the motion. 
Factors effecting Frictional Force: 
1. Roughness of the surfaces – Rough surfaces have more irregularities, which lead to more frictional force 
between them.  
2. Area of contact – If the pressure on the surface is kept constant frictional force increases with area of 
contact. More area of contact means more roughness, which leads to more friction. 
3. Force applied – Increase in force will increase the area of contact by pushing the two surfaces close to 
each other, which leads to increased friction. 
 
Effects of friction 
1. It helps to stop a moving object. The object will never stop moving without friction. 
2. Friction produces heat, which helps in burning of matchstick. 
3. Rubbing of hands produces heat due to friction, which provide warmth during winters. 
Friction as evil 
1. It leads to wearing and tearing off shoes, tires and motor parts in engines. 
2. Heat is released during friction between various parts of the engine; it increases the energy consumption 
of the machine. 
Increasing the Friction 
1. By increasing the roughness such as in case of tires, sports shoes etc. 
2. By increasing the area of contact between the surfaces. 
3. By increasing the force on the object. 
Decreasing the Friction 
1. By increasing the smoothness of the object. 
2. By using lubricants such as powder on a carom board and oil between the machine parts. Air cushions 
are also used as lubricants in some cases to reduce friction. 
3. Wheels can reduce the friction as they reduces the area of contact between the surfaces. 
Types of Friction 
1. Sliding Friction – The frictional force between two surfaces when one or both of them slides over the 
other. E.g. Pushing a block of wood. 
2. Rolling Friction – The frictional force between two surfaces when one or both the surfaces roll over 
each other. E.g. A moving car or cart. Rolling friction is lower than the sliding friction because the area 
of contact is less in in rolling friction. 
3. Drag – The frictional force exerted by fluid (liquid and gases) on the objects is called drag. E.g. Force 
exerted by air on a moving car. 
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