Q1. Friction is a _________ force.

Ans: Contact

Q2. Friction always acts in the _________ direction to motion.

Ans: Opposite

Q3. SI unit of frictional force is _________.

Ans: Newton (N)

Q4. The force opposing relative motion between surfaces is _________.

Ans: Friction

Q5. True or False: Friction can produce heat.

Ans: True

Q6. The cause of friction is _________.

Ans: Irregularities of surfaces

Q7. Friction is more on a _________ surface.

Ans: Rough

Q8. Friction is less on a _________ surface.

Ans: Smooth

Q9. Static friction is _________ than kinetic friction.

Ans: Greater

Q10. Lubricants are used to _________ friction.

Ans: Reduce

Q11. The friction that allows walking is _________.

Ans: Static friction

Q12. Ball bearings are used to _________ friction.

Ans: Reduce

Q13. The friction in fluids is called _________.

Ans: Drag

Q14. Shape of aeroplanes is designed to reduce _________.

Ans: Air resistance

Q15. Sliding friction is _________ than rolling friction.

Ans: Greater

Q16. Matchstick lights due to _________.

Ans: Friction

Q17. True/False: Friction is always harmful.

Ans: False

Q18. Friction between tyres and road helps in _________.

Ans: Motion and stopping

Q19. Grease, oil, or powder used to reduce friction are called _________.

Ans: Lubricants

Q20. Fluid friction increases with _________.

Ans: Speed

Q21. Streamlined shapes are designed to _________ drag.

Ans: Reduce

Q22. Advantages of friction include _________ and _________.

Ans: Writing, walking

Q23. Disadvantage of friction is _________ of machines.

Ans: Wear and tear

Q24. Friction generates _________.

Ans: Heat

Q25. The least friction is offered by _________.

Ans: Rolling

Q26. Friction is necessary for _________.

Ans: Gripping

Q27. Sports shoes have grooves to _________ friction.

Ans: Increase

Q28. Which has less drag—bird or flat board?

Ans: Bird

Q29. Friction in fluids is also called _________.

Ans: Viscous force

Q30. The invention of _________ is due to friction.

Ans: Fire

 Short & Long Answer Questions 

Q31. Define friction.

Ans: The force that opposes motion between two surfaces in contact.

Q32. State two causes of friction.

Ans: Microscopic irregularities and interlocking of projections.

Q33. Why is friction a necessary evil?

Ans: It helps in walking/writing but also causes wear/heat.

Q34. Differentiate between static and sliding friction.

Ans: Static opposes starting motion, sliding acts during motion.

Q35. Why is sliding friction less than static friction?

Ans: Interlocking is less during motion.

Q36. Give one example where friction is desirable.

Ans: Writing with a pen.

Q37. Give one example where friction is undesirable.

Ans: Wear of machine parts.

Q38. Why do we use lubricants?

Ans: To fill gaps and reduce irregularities, lowering friction.

Q39. Why is rolling friction less than sliding friction?

Ans: Rolling reduces contact area and interlocking.

Q40. Give an example of rolling friction in daily life.

Ans: Ball bearings in machines.

Q41. Explain fluid friction.

Ans: Resistance offered by liquids or gases to objects moving through them.

Q42. Why do cars have streamlined shapes?

Ans: To reduce air drag.

Q43. Why do ships have streamlined shapes?

Ans: To reduce water resistance.

Q44. Why are tyres of vehicles grooved?

Ans: To increase grip and prevent slipping.

Q45. Why are soles of shoes patterned?

Ans: To increase friction for walking safely.

Q46. What happens when friction is too high?

Ans: Excess heat, energy loss, wear and tear.

Q47. What happens when friction is too low?

Ans: Slipping, difficulty in movement.

Q48. Why do objects slow down when moving on a surface?

Ans: Opposing frictional force.

Q49. Why do we sprinkle powder on carrom board?

Ans: To reduce friction and allow smooth sliding.

Q50. Why do matchsticks light when rubbed?

Ans: Friction produces heat that ignites chemicals.

Q51. Why do brake pads wear out?

Ans: Due to high friction during braking.

Q52. Why is friction less on ice?

Ans: Smooth surface reduces irregularities.

Q53. Why is friction important for writing?

Ans: Friction between pen and paper leaves marks.

Q54. How does friction help in walking?

Ans: It provides grip for feet to push backward.

Q55. Give one method to increase friction.

Ans: Using rough surfaces or grooves.

Q56. Give one method to decrease friction.

Ans: Applying lubricants.

Q57. Explain why we use ball bearings in wheels.

Ans: To convert sliding into rolling, reducing friction.

Q58. Why do aeroplanes and birds have streamlined bodies?

Ans: To reduce air resistance.

Q59. Why is friction called self-adjusting?

Ans: It increases until maximum limit to oppose applied force.

Q60. Differentiate between static, sliding, and rolling friction.

Ans: Static (before motion), sliding (during sliding), rolling (least, during rolling).

Q61. Why is it difficult to move a heavy box at rest?

Ans: High static friction.

Q62. Why is it easier to move the box once it starts sliding?

Ans: Sliding friction is less than static.

Q63. Why do rockets have pointed shapes?

Ans: To cut through air, reducing drag.

Q64. Why do swimmers wear special suits?

Ans: To reduce fluid resistance.

Q65. Why do tyres wear out after long use?

Ans: Due to continuous friction with road.

Q66. Why does rubbing hands produce heat?

Ans: Friction converts kinetic energy into heat.

Q67. How is friction both useful and harmful in daily life?

Ans: Helps in grip and writing, but causes wear and energy loss.

Q68. Explain how lubrication reduces friction.

Ans: It fills gaps, smoothens surface, reduces interlocking.

Q69. Why is it difficult to ride a bicycle without grease on its chain?

Ans: High friction without lubrication.

Q70. Explain why objects moving in air experience resistance.

Ans: Due to air molecules colliding against object’s surface.

 Numerical / Application Questions 

Q71. A box requires 100 N force to just start moving. What is the limiting friction?

Ans: 100 N

Q72. A 5 kg block lies on surface, μ = 0.4, g=10. Find friction.

Ans: F = μN = 0.4×50=20 N

Q73. A 10 kg block on table, μ=0.3. Find max static friction. (g=10)

Ans: N=100 N, Fs=0.3×100=30 N

Q74. A block weighs 200 N, μ=0.25. Find limiting friction.

Ans: F=0.25×200=50 N

Q75. A box of mass 20 kg requires 80 N to move. Find μ. (g=10)

Ans: N=200 N, μ=80/200=0.4

Q76. A 50 N block slides with force 15 N. If μ=0.3, does it move?

Ans: N=50, Fs=15 N < μN=15 N → Just starts moving

Q77. A 5 kg block, μ=0.2. Find frictional force. (g=10)

Ans: N=50, F=0.2×50=10 N

Q78. Weight=100 N, μ=0.1. Find force needed to slide it.

Ans: F=0.1×100=10 N

Q79. A 200 N block is pulled with 60 N. μ=0.25. Will it move?

Ans: Max friction=0.25×200=50 N < 60 → Yes

Q80. A 300 N block, μ=0.2. Find limiting friction.

Ans: 0.2×300=60 N

Q81. A 25 kg block on floor, μ=0.4. Find force required to move it. (g=10)

Ans: N=250, F=0.4×250=100 N

Q82. Force=40 N applied, μ=0.2, mass=15 kg. Will it move? (g=10)

Ans: N=150, Fs=30 N < 40 → Yes

Q83. A car tyre has μ=0.5. Weight=1000 N. Max friction?

Ans: 0.5×1000=500 N

Q84. A truck weight=20,000 N, μ=0.4. Find limiting friction.

Ans: 0.4×20,000=8000 N

Q85. A person pushes box of mass 10 kg with 25 N. μ=0.2. g=10. Will it move?

Ans: N=100, Fs=20 N < 25 → Yes

Q86. Frictional force=50 N, area=0.5 m². Pressure?

Ans: 50/0.5=100 Pa

Q87. A scooter tyre μ=0.6, weight=2000 N. Max friction?

Ans: 1200 N

Q88. A horse pulls cart of 1000 N. If μ=0.4, normal=1000 N, friction=?

Ans: 400 N

Q89. A block of 15 kg slides. μ=0.3. Find force needed. (g=10)

Ans: N=150, F=45 N

Q90. Car of mass 1000 kg, μ=0.5. Max braking force?

Ans: N=10000, F=5000 N

Q91. μ=0.25, block weight=400 N. Limiting friction?

Ans: 0.25×400=100 N

Q92. A 2 kg block slides with μ=0.1. g=10. Find friction.

Ans: N=20, F=2 N

Q93. A 500 N block, μ=0.3. Force required?

Ans: 0.3×500=150 N

Q94. A block 50 kg, μ=0.4. Find max static friction. (g=10)

Ans: N=500, F=200 N

Q95. μ=0.2, mass=30 kg, g=10. Frictional force=?

Ans: N=300, F=60 N

Q96. A 10 kg block needs 45 N to slide. μ=? (g=10)

Ans: N=100, μ=45/100=0.45

Q97. A car mass 800 kg, μ=0.5. Max friction?

Ans: N=8000, F=4000 N

Q98. A bike of weight 1500 N, μ=0.4. Max friction?

Ans: 600 N

Q99. Block mass=40 kg, μ=0.35. Force required? (g=10)

Ans: N=400, F=140 N

Q100. A 1000 N block on surface, μ=0.2. Find limiting friction.

Ans: 0.2×1000=200 N