Question

Three examples where friction is (a)useful (b) not useful

Answer 1

three useful example are following:-

• it helps in walking , running.
• It helps to writing and making drawing
• It helps to hold the nails and screws on the wall and the wood

three unuseful example are following:-

• It causes wear and tear.
• it reduce the speed of moving vehicle to great extent.
• it causes between branches of trees which rub against each other , forest fire occurs.

I hope this answers help you.

thanks

Answer 2

$\huge{\textsf{\red{\underline{\underline{Advantages\;of\;Friction}}}}}$

✿ It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it becomes difficult to walk due to low friction of ice.

✿ We can not fix nail in the wood or wall if there is no fiction. It is friction which holds the nail.

✿ A horse cannot pull a cart unless friction furnishes him a secure Foothold.

$\huge{\textsf{\red{\underline{\underline{Disadvantages\;of\;Friction}}}}}$

✿ The main disadvantage of friction is that it produce heat in various parts of machines. In this way some useful energy is wasted as heat energy.

✿ Due to friction we have to exert more power in machines.

✿ It opposes the motion.

✿ Due to friction, noise is also produced in machines.

✿ Due to friction, engines of automobiles consume more fuel which is money loss.

$\huge{\textsf{\red{\underline{\underline{Methods\;of\;reducing\;Friction}}}}}$

✿ Use of lubricants:

The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity.

✿ Use of Grease:

Proper greasing between the sliding parts of machine reduces the friction.

✿ Use of ball bearing:

In machines where possible, sliding friction can be replaced by rolling friction by using ball bearing.

✿ Design modification:

Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction.