Question

explain fully the terms friction and limiting friction. state the laws of limiting friction .justify the statement that friction is a necessary and a evil. give some familiar methods for reducing friction
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Answer 1

Answer:

Friction is a force that opposes motion between any surfaces that are touching. Friction can work for or against us.Friction occurs because no surface is perfectly smooth. Even surfaces that look smooth to the unaided eye make look rough or bumpy when viewed under a microscope. Look at the metal surfaces in the Figure below. The aluminum foil is so smooth that it's shiny. However, when highly magnified, the surface of metal appears to be very bumpy. All those mountains and valleys catch and grab the mountains and valleys of any other surface that contacts the metal. This creates friction.

Answer 2

Friction:

whenever 2 surfaces move against eachother a force of resistance is generated in opposition to direction of motion, this force is termed as friction. The root cause of friction force is the intermolecular interaction. The molecules of both surfaces attract the other surface molecules which hinder the movement.

eg- when on black borad you write something woth chalk and leave it for some days you will find that chalk is difficult to erase this is beacuse of molecular attraction between chalk and blackborad molecules.

LIMITING FRICTION : When the 2 surfaces are in rest they have static friction in between them. To move them against each other we must apply the force more than friction. The maximum static friction after which the body will start moving is called limiting friction.

FRICTION IS A NECESSARY EVIL-

Friction is very harmful but at the same time its very useful too. so its referred to as necessary evil. Because of friction only we are able to move on ground, write on paper with pen, move on vehicles, you can hold things in your hand, the spin in cricket ball is also a result of friction itself. It has some disadvantages too like, it cause wear and tear of machines part, it wastes energy as too overcome frcition we apply more energy than it... hence we can say that even it is disadvantageous but life will be impossible in absence of it. So its a necessary evil.

REDUCING FEICTION-

1. oiling makes surface smooth and surfaces easily slide.

2. greasing is same as oiling

3. lubrication also makes surface smooth

4. reducing area of contact between surfaces as friction os directly proportional to area of contact.

5.for objects moving in fluids the body should be streamlined.

6. where objects are rolled use of ball bearing is useful.

hope its helpful