CBSE · NCERT · Class 8 Science · Chapter 9

NCERT Solutions: Class 8 Science Chapter 9 - Friction

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Chapter-wise NCERT intext questions and exercise answers for Friction, grounded in the official textbook.

Questions are taken verbatim from the NCERT textbook; answers were grounded against the chapter's content during generation. Items needing review are marked.
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Exercises 10
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1Exercises10 questions
Q.1Fill in the blanks about friction.v
Answer:

(a) motion (b) nature (c) heat (d) reduces (e) less.

Q.2Arrange rolling, static and sliding frictions in decreasing order.v
  1. a. rolling, static, sliding
  2. b. rolling, sliding, static
  3. c. static, sliding, rolling
  4. d. sliding, static, rolling
Answer:

(c) static, sliding, rolling.

Q.3Friction on toy car in increasing order on wet marble, dry marble, newspaper and towel isv
  1. a. wet marble floor, dry marble floor, newspaper and towel
  2. b. newspaper, towel, dry marble floor, wet marble floor
  3. c. towel, newspaper, dry marble floor, wet marble floor
  4. d. wet marble floor, dry marble floor, towel, newspaper
Answer:

(a) wet marble floor, dry marble floor, newspaper and towel.

Q.4A book slides down a tilted desk. Show the direction of friction.v
Answer:

Friction acts up the inclined surface, opposite to the downward sliding motion.

Q.5Would soapy water on a marble floor make walking easier or difficult? Why?v
Answer:

More difficult, because soap reduces friction and makes the floor slippery.

Q.6Why do sportsmen use shoes with spikes?v
Answer:

Spikes increase friction with the ground and give better grip.

Q.7Who must apply a larger force: Iqbal pushing a lighter box or Seema a heavier box?v
Answer:

Seema, because a heavier box presses harder on the floor and produces greater friction.

Q.8Why is sliding friction less than static friction?v
Answer:

Once surfaces start sliding, their contact interlocking is reduced compared with the force needed to start motion.

Q.9Give examples showing friction is both friend and foe.v
Answer:

Friction helps us walk, write, hold objects and stop vehicles using brakes. It is a foe because it causes wear and tear, produces unwanted heat and wastes energy in machines.

Q.10Why must objects moving in fluids have special shapes?v
Answer:

Streamlined shapes reduce fluid friction or drag, allowing easier and faster motion.