Theory:

Advantages of friction:
 
Friction is required in our daily activities.
  • Friction is a very important part of our lives; if you want to hold anything, there need to be friction  between your hand and the material.
  • In a moving vehicle, friction is present between tyres and the road.
  • To tie a knot, type a letter, or write a word, there should be friction between your hand and the other body.
  • Because of the friction, writing with a pen on paper is quick and easy.
  • We can light a matchstick, sew clothes, and hammer a nail into the wall due to friction.
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A boy holds a lamb
Though friction hinders the motion of the body, it is a necessary element in our day to day life.
 
Disadvantages of friction:
  • In big machineries, friction should be strictly avoided for the smooth functioning of the machine without any wear and tear.
  • In a running machine, between two metal parts or screws, if they collide due to friction, chances are high that they rub against each other and there are chances of fire sparks also.
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Friction between two metal surfaces
 
Increasing and decreasing Friction
 
a) Area of contact
The area of the surfaces in contact can be increased to increase friction. For example, brake shoes in a cycle have to be adjusted so that they are as close as possible to the rim of the wheel, in order to increase the friction.
 
b) Using lubricants
 Lubricants are fluids that reduce the frictional force between two objects. For example, castor oil, ghee, grease, etc.
When applied over metal parts, lubricants fill up the gaps in irregular surfaces between objects in contact and provide a smooth layer between the two objects, thus reducing friction.
 
Lubricants are by design attached to the frictional portions in machinery, as shown in the picture below:
 
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Heavy machineries
  
c) Using ball-bearing
Sliding is replaced by rolling with the help of ball bearings, because rolling friction is lower than sliding friction. Lead shots are used in the bearing of a cycle hub for the same reason.
 
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Ball-bearing
Reference:
Boy holding a goat image : Image by Sasin Tipchai from Pixabay -https://pixabay.com/photos/boys-outdoor-thailand-baby-mammal-1807545/
Lubricant fitted machine :  Image by olafpictures from Pixabay  - https://pixabay.com/photos/germany-dortmund-zeche-zollern-2284072/
Spark image : Image by Free-Photos from Pixabay
https://commons.wikimedia.org/wiki/File:Angular-contact-ball-bearing_single-row_din628_type-b.png