Class 8 Science Chapter 9 Important Question Answers - Friction

Q1: Why do objects slow down and eventually stop when no external force is applied to them?
Ans: Objects slow down and stop because of the force of friction acting in the opposite direction of their motion.

Q2: Explain how the force of friction opposes the applied force on an object.
Ans: The force of friction opposes the applied force by exerting a force in the opposite direction to the motion, making it difficult for the object to move.

Q3: Is the force of friction the same for all surfaces? Does it depend on the smoothness of the surfaces?
Ans: No, the force of friction is not the same for all surfaces. It depends on the roughness or smoothness of the surfaces in contact. Rough surfaces have greater friction compared to smooth surfaces.

Q4: How do irregularities on surfaces contribute to the force of friction?
Ans: Irregularities on surfaces create interlocking between them, which increases friction. Even seemingly smooth surfaces have microscopic irregularities that contribute to friction.

Q5: Explain the difference between static friction and sliding friction.
Ans: Static friction is the force required to overcome the initial resistance of an object at rest, while sliding friction is the force required to keep an object moving at a constant speed.

Q6: Why is friction described as a necessary evil in the chapter?
Ans: Friction is necessary because it allows us to walk, write, drive vehicles, and perform various tasks. However, it is also considered evil because it wears out materials, produces heat, and leads to energy loss.

Q7: How does friction play a role in the ability to hold objects, like a glass tumbler?
Ans: Friction provides the grip necessary to hold objects. Without friction, it would be difficult to hold objects securely, especially if they are smooth or greasy.

Q8: Why is friction essential for walking on wet and slippery surfaces?
Ans: Friction provides the necessary traction to prevent slipping on wet and smooth surfaces. Without friction, walking on such surfaces would be extremely challenging.

Q9: How does friction affect the ability to write with a pen or pencil?
Ans: Friction between the pen or pencil tip and the writing surface allows ink or graphite to be transferred, enabling writing. Without friction, writing would not be possible.

Q10: Explain how friction plays a crucial role in stopping vehicles and turning them.
Ans: Friction between vehicle tires and the road surface allows for braking, stopping, and changing direction. Without friction, vehicles could not be controlled.

Q11: Why is reducing friction necessary in some situations? Provide examples.
Ans: Reducing friction is necessary to increase efficiency and reduce wear and tear. Examples include using lubricants like oil or grease to reduce friction in machines and applying powder on carrom boards.

Q12: How do lubricants reduce friction in machines?
Ans: Lubricants form a thin layer between moving surfaces, preventing direct contact and reducing friction. This makes movement smoother and more efficient.

Q13: Explain the concept of rolling friction. Why is it easier to roll an object than to slide it?
Ans: Rolling friction is the resistance to motion when one body rolls over another. It is easier to roll an object than to slide it because rolling friction is smaller than sliding friction.

Q14: Why are ball bearings used in machines like ceiling fans and bicycles?
Ans: Ball bearings are used to replace sliding friction with rolling friction, making machines more efficient and reducing wear and tear.

Q15: How does fluid friction affect objects moving through air and liquids? Why is it important to minimize fluid friction in design?
Ans: Fluid friction affects objects by creating resistance as they move through air or liquids. Minimizing fluid friction is important to reduce energy loss. Engineers take inspiration from nature to design shapes that minimize fluid friction, as seen in the shapes of vehicles like airplanes.