Question

explain why sliding friction is less than static friction

give example to show that friction is both a friend and a foe

explain why objects moving in fluids must have special shapes​

Answer 1

Answer:

During sliding, contact points do not get enough time to get interlocked properly. Therefore, less friction. But, when the object is at rest, the surfaces interlock well, therefore friction is more. This explains why sliding friction is less than static friction.

Examples to show that friction is a friend and a foe: Friction is friend: (i) Friction allows us to grip and catch different objects. (ii) It helps us to walk comfortably on the surface. ... Friction is foe: (i) Friction causes wear and tear in objects. (ii) It causes damage to the parts of machines.

Special shapes experience less fluid friction, therefore, can move easily through fluids. ... Keeping all these things into consideration the shape of the ship is made in such a way that it experiences less fluid friction i.e. drag.

Answer 2

Required Answer:

Answer 1st:

$\longmapsto$ Sliding friction is the frictional force offered when sliding an object whereas static friction is the force of friction in static or stationary situation. So, when the object made to slide, the contact of two points on its surface don't get enough time to interlock. That's why sliding friction ie smaller than static friction.

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Answer 2nd:

$\longmapsto$ Examples to show that friction is both a friend and a foe:

Friction as friend:

• Friction helps to walk and run : There is friction between our foot and the ground that helps us to walk. It prevents us from slipping.

• Friction helps in writing : Friction helps in writing, if there will be no friction we would not be able to hold a pen vertically. Friction that opposes slipping help us to hold the pen.

• Friction helps to produce heat : When we rub matchstick against the side of the matchbox, because of friction it lights up.

As foe (enemy):

• Cause waste of fuel : Since, machines are worked due to friction, in that case a large amount of fuel is wasted to run the machines .

• Production of heat by friction can cause damage : Since, friction also produces heat .So, the engines of car and other machinery can become hot after running some time.

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Answer 3rd:

$\longmapsto$ Objects moving in fluid must have special shapes because that special shapes help them to move through the fluid easily as that special shapes reduce the friction between their body and water.

For example : Fishes have streamlined body that reduces the friction between their body and water and helps them to swim.

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