Tag: friction

Questions Related to friction

A sphere $S$ roll without slipping, moving with a constant speed on a plank $P.$ The fraction between the upper surface of $P$ and the sphere is sufficient to prevent slipping, while the lower surface of $P$ is smooth and rests on the ground. Initially, $P$ is fixed to the ground by a pin $N.$ If $N$ is suddenly removed:

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. S will begin to slip on P

  2. P will begin to move back wards

  3. the speed of s will decrease, and its angular velocity will increase

  4. there will be no charge in the motion of S and P will still be at rest

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Correct Option: D

Why do we sprinkle powder before playing carroms?

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. To increase friction

  2. To decrease friction

  3. To increase or decrease the friction depending on the type of the game played

  4. None of these

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Correct Option: B
Explanation:

It is done just to reduce the friction. On microscopic level, the powder particles offer rolling friction to the striker because of which the striker can be rolled around smoothly.

State whether the statements are true or false:
Oil is used to reduce the friction on door hinges.

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. True

  2. False

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Correct Option: A
Explanation:

Lubrication is another way to make a surface smoother. A lubricant is a slippery substance designed to reduce the friction between surfaces, Since the door hinges are exposed to the atmosphere the chances of corrosion increases and the surface becomes irregular enough to promote friction. Applying oil on the door hinges can reduce the amount of friction and thus it will decrease it.

Friction should always be avoided.

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. True

  2. False

Show answer
Correct Option: B
Explanation:
The given statement is false.
Friction is a necessary evil because without friction we will not be able to set our bodies in motion or stop the bodies which are in motion. Friction is absolutely necessary in our day to day activities. For eg it is the friction on the ground that helps us to walk and without friction it would not have veen possible to write on a paper.
Hence friction is important and cannot be avoided.

Friction is a force that oppose motion.

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. True

  2. False

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Correct Option: A
Explanation:

The given statement is true.

Friction always acts in opposite direction to movement i.e it opposes the motion of an object. Air resistance is a frictional force which opposes motion through air.

The efficiency of machine is reduced due to friction.

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Yes, the statement is true.

Friction introduces losses and decreases efficiency since friction generates heat which is an energy that should be converted in movement. That energy in the form of heat is a loss. Also friction increases increases the wear and tear of a machine thereby decreasing its efficiency.

A coin flicked across a table will stop, because :

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. It is heavy

  2. No force is acting on it

  3. Earth attracts the coin

  4. Table exerts a frictional force

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Correct Option: D
Explanation:

According to the first law of motion a body will remain in the state of rest or of uniform motion until or unless compelled by an external force.

In this case the coin will stop because an external force is exerted in the form of frictional force by the table that opposes the motion of the flicked coin.

Hence, correct answer is option $D$

The application of decreasing friction includes :

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. Ball bearing used in moving parts of a machine

  2. The streamlined shape of an aircraft

  3. The layer of air between the hull of a hovecraft.

  4. None of these.

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Correct Option: A,B,C
Explanation:

The application of decreasing friction is
(i) Ball bearings used in moving parts of a machine.
(ii) The stream lines shape of an aircraft.
(iii) The layer of air between the hull of a hovecraft.

Which of the following are done to increase  friction?

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. Making groove in the shoes

  2. polishing rough surface

  3. using ball bearing in wheels

  4. Creating an air cushion

Show answer
Correct Option: A
Explanation:

Soles of shoes are grooved because the grooves increases the friction and gives the good grip to the person while walking with shoes