Theory:

What is the difference between a worn-out tyre and a new tyre?
The only difference between the worn-out tyre and the new tyre is the tread. New tyres have tread in them, whereas the old tyre has no tread. Due to friction, the tread gets damaged in the old tyres. This causes less grip between the road and the tyres. So, it is difficult to stop the moving car with old tyres. One has to replace the old tyre with a new one to avoid accidents.
 
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Old worn-out tyres
 
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New tyres
 
In the above example, we add tread to increase the friction. There are countless situations in our real-life where we increase the friction. To get a better grip, kabaddi players rub their hands with soil. Gymnasts apply some coarse substance on their hands for better grip.
 
But in some situations, friction is undesirable, and we would want to minimize it.
 
Why do you sprinkle fine powder on the carrom board?
 
While playing carrom, you must have used powder to make the striker move smoothly over the board. So to reduce the friction between the board and the striker, we are using powder. The powder fills the gap present in the irregularities and makes the striker move smoothly over the board.
 
When we apply oil, grease, or graphite between a machine's moving parts, a thin layer is formed, and moving surfaces do not directly rub against each other. The interlocking of irregularities is avoided due to the presence of oil or greases between them.
Lubricants:
The substances which we use to reduce friction are called lubricants.
The presence of an air cushion between the moving parts reduces friction in some machines. In some devices, it may not be advisable to use oil or grease as a lubricant.
shutterstock_1166332111.jpgThe presence of powder reduces the friction between the striker and the board.
shutterstock_117283822 (1).jpgWe use oil and grease in some moving parts to reduce friction.
shutterstock_1823531798.jpg A few drops of oil are poured on the hinges of a door for smooth movement.