4. What kind of substances are known as lubricants?
a) Increase friction
b) Decrease friction
c) Increase or decrease friction
d) None of these
Answer: b) Decrease friction :cite[1]:cite[4]
5. Which of the following produces least friction?
a) Sliding friction
b) Rolling friction
c) Static friction
d) Fluid friction
Answer: b) Rolling friction :cite[4]:cite[10]
6. The shape of an airplane is like a:
a) Dog
b) Bird
c) Car
d) All of these
Answer: b) Bird :cite[1]:cite[4]
7. If we apply oil on door hinges, the friction will:
a) Increase
b) Decrease
c) Disappear altogether
d) Remain unchanged
Answer: b) Decrease :cite[2]:cite[4]
8. Friction due to fluids is called:
a) Drag
b) Drop
c) Dru
d) Drown
Answer: a) Drag :cite[4]:cite[10]
9. Which of the following is responsible for wearing out of bicycle tyres?
a) Muscular force
b) Magnetic force
c) Frictional force
d) Electrostatic force
Answer: c) Frictional force :cite[4]:cite[10]
10. What is the direction of force of friction acting on a moving object?
a) Same direction as motion
b) Opposite direction of motion
c) Perpendicular to direction of motion
d) Does not act on moving objects
Answer: b) Opposite direction of motion :cite[2]:cite[10]
Short Answer Questions (7 questions)
1. Why is it difficult to walk on a wet marble floor?
Hint/Answer: The wet marble floor has less friction due to the water layer, making it difficult to walk without slipping :cite[4]:cite[10].
2. Explain why the soles of shoes and tyres of vehicles are grooved.
Hint/Answer: Grooves are designed to increase friction by providing better grip on surfaces, preventing slipping :cite[10].
3. Give two examples where friction is undesirable.
Hint/Answer: Friction is undesirable in machine parts (causes wear and tear) and when trying to move heavy objects (requires more force) :cite[5]:cite[7].
4. Why do we shape airplanes like birds?
Hint/Answer: Airplanes are shaped like birds to reduce fluid friction (drag) by having a streamlined shape, allowing easier movement through air :cite[4]:cite[10].
5. Our hands become warm when we rub them. Why?
Hint/Answer: Rubbing hands together produces heat due to friction between the surfaces :cite[10].
6. What are lubricants? How do they help?
Hint/Answer: Lubricants are substances (like oil or grease) that reduce friction between moving surfaces by forming a thin layer :cite[1]:cite[4].
7. Why is rolling friction less than sliding friction?
Hint/Answer: In rolling friction, the area of contact is minimal (point of contact) and the surfaces don't get locked, whereas in sliding friction, larger surface areas are in contact and interlock :cite[10].
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