Willer Academy

Class 8 Science Test

Chapter: Friction

Multiple Choice Questions (10 questions)

1. Friction always ____________

• a) helps the motion
• b) opposes the motion
• c) both of these
• d) none of these

Answer: b) opposes the motion :cite[1]:cite[4]

2. Which type of surface produces less friction?

• a) Rough surface
• b) Smooth surface
• c) Both have same friction
• d) None of these

Answer: b) Smooth surface :cite[1]:cite[4]

3. Friction is a __________

• a) Non-contact force
• b) Contact force
• c) Magnetic force
• d) Electrostatic force

Answer: b) Contact force :cite[1]:cite[4]

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].