Friction Class 8 Chapter 9 Quiz" tests your understanding of the concepts of friction, including its causes, effects, types, and applications in daily life. This quiz covers static, sliding, and rolling friction, factors affecting friction, advantages, disadvantages, and methods to reduce or increase friction. It’s designed to reinforce key concepts and evaluate your knowledge effectively.
1) Why does a vehicle slow down when brakes are applied?
Answer: A vehicle slows down when brakes are applied because friction opposes its motion, causing it to decelerate.
2) What happens to a moving object when no external force is applied to it?
Answer: When no external force is applied to a moving object, friction between the object and the surface opposes its motion, eventually bringing it to a stop.
3) Why does a moving ball on the ground stop after some time?
Answer: A moving ball on the ground stops after some time due to the force of friction acting between the ball and the surface.
4) Why do we slip when we step on a banana peel?
Answer: We slip when we step on a banana peel because it reduces friction between our foot and the ground, making the surface slippery.
5) Why is it difficult to walk on a smooth and wet floor?
Answer: It is difficult to walk on a smooth and wet floor because the friction between the floor and our feet is greatly reduced, making it harder to maintain grip and balance.
6) What happens when a book is pushed on a table?
Answer: When a book is gently pushed on a table, it stops after moving a short distance. This happens because the force of friction opposes the motion of the book.
7) What is the force called that opposes the motion of an object?
Answer: The force that opposes the motion of an object is called the force of friction.
8) What happens when force is applied to an object in terms of friction?
Answer: When force is applied to an object, friction always acts in the opposite direction to the applied force, opposing the motion of the object.
9) Is friction the same for all surfaces?
Answer: No, friction is not the same for all surfaces. It depends on the smoothness and texture of the surfaces in contact.
10) What is used to measure the force of friction between the surface of the brick and the floor?
Answer: The force of friction between the surface of the brick and the floor is measured using a spring balance.
11) Why do the readings of the spring balance change in polythene and jute?
Answer: The readings change because different materials (polythene and jute) affect the smoothness and texture of the surface, thereby altering the frictional force.
12) What is a spring balance?
Answer: A spring balance is a device used for measuring the force acting on an object. It consists of a coiled spring that stretches when a force is applied. The stretching is measured by a pointer on a graduated scale, showing the magnitude of the force.
13) What is the effect of the surface on which the pencil cell moves?
Answer: The distance covered by the pencil cell depends on the nature of the surface. Smooth surfaces allow the pencil cell to move farther, while rough surfaces reduce the distance due to greater friction.
14) Could the smoothness of the pencil cell’s surface affect the distance it travels?
Answer: Yes, the smoothness of the pencil cell’s surface can also affect the distance it travels. A smoother surface reduces friction, allowing the pencil cell to move farther.
15) What happens if the pencil cell is wrapped with sandpaper?
Answer: Wrapping the pencil cell with sandpaper increases the friction between the pencil cell and the surface, reducing the distance it travels.
16) What causes friction between two surfaces?
Answer: Friction is caused by irregularities on the two surfaces in contact. Even surfaces that appear smooth have minute irregularities that interlock and resist motion.
17) Why is friction greater on rough surfaces?
Answer: Friction is greater on rough surfaces because they have a larger number of irregularities, leading to stronger interlocking between the surfaces.
18) Why is the distance covered by the pencil cell different on various surfaces?
Answer: The distance covered by the pencil cell varies because of differences in friction on different surfaces. Rough surfaces produce more friction, reducing the distance, while smoother surfaces have less friction, allowing the pencil cell to travel farther.
19) What causes friction?
Answer: Friction is caused by the interlocking of irregularities between two surfaces in contact.
20) How does pressing surfaces harder affect friction?
Answer: Increasing the pressure between two surfaces increases the force of friction.
21) Give an example of how pressure affects friction.
Answer: It is easier to drag a mat when no one is sitting on it compared to when someone is sitting on it, demonstrating the effect of increased pressure on friction.
22) How does the surface texture of objects affect friction?
Answer: Rough surfaces, like an earthen pot (kulhar) , have more irregularities and thus more friction than smooth surfaces, like a glass tumbler. A greasy or oily surface reduces friction as it fills the irregularities.
23) Why is friction important for walking?
Answer: Friction between our shoes and the ground allows us to push against the ground and move forward. Without friction, we would slip and slide.
24) How does friction affect writing?
Answer: Friction between the pen or pencil tip and the paper allows the ink or graphite to transfer, enabling us to write. Chalk sticks to the blackboard due to friction between the chalk and the board.
25) What is the difference between static and sliding friction?
Answer: Static friction: The force required to overcome friction and start an object moving from rest.
Sliding friction: The force required to keep an object moving at a constant speed.
26) Why is static friction generally greater than sliding friction?
Answer: When an object is at rest, the irregularities on its surface have more time to lock into the irregularities on the surface it's resting on. Once the object starts moving, these irregularities have less time to interlock, reducing the friction.
27) What would happen if there were no friction between objects?
Answer: Without friction: Objects in motion would never stop, tyres of automobiles could not start, stop, or change direction, activities like fixing a nail on the wall or tying a knot would be impossible and the Construction of buildings would not be possible.
28) How does friction affect the soles of shoes and other materials?
Answer: Friction causes wear and tear:
The soles of shoes wear out due to continuous friction.
Materials like screws and ball bearings also get worn out over time.
Steps of foot over-bridges often appear worn out at railway stations because of friction.
29) Can friction produce heat? Give examples.
Answer: Yes, friction can produce heat. Examples include:
Rubbing palms together generates warmth.
Striking a matchstick against a rough surface produces fire.
The jar of a mixer becomes hot after running for some time.
30) What is the disadvantage of heat produced by friction in machines?
Answer: The heat generated by friction in machines leads to energy wastage and reduces efficiency.
31) Why is friction both useful and harmful?
Answer: Friction is useful because it helps in:
Starting, stopping, and changing the direction of motion.
Activities like tying knots and constructing buildings.
Friction is harmful because:
It causes wear and tear of materials.
It produces heat, leading to energy loss.
32) Why are the soles of shoes grooved?
Answer: The soles of shoes are grooved to provide a better grip on the floor, ensuring safe movement.
33) Why are the tyres of cars, trucks, and bulldozers treaded?
Answer: Treaded tyres increase friction, providing a better grip on the ground, which helps in safe and stable movement.
34) How do we deliberately increase friction?
Answer: Brake pads in bicycles and automobiles increase friction to stop the wheels.
Kabaddi players rub their hands with soil for a better grip.
Gymnasts use coarse substances on their hands to improve grip.
35) In which situations is friction undesirable?
Answer: Friction is undesirable when it causes inefficiency or wear, such as:
On carrom boards, where the powder is sprinkled to reduce friction.
On door hinges, where oil is applied for smooth movement.
In machines, where grease is used between moving parts to reduce friction.
36) What substances are used to reduce friction?
Answer: Lubricants like oil, grease, or graphite form a thin layer to reduce direct rubbing between surfaces.
An air cushion can also be used in some machines to minimize friction.
37) How does applying lubricants reduce friction?
Answer: Lubricants form a thin layer between moving surfaces, avoiding direct contact and interlocking of irregularities, making movement smoother.
38) Can friction ever be eliminated?
Answer: No, friction can never be eliminated because no surface is perfectly smooth. Some irregularities are always present.
39) Why is it easier to pull luggage fitted with rollers?
Answer: Rolling friction is smaller than sliding friction. Rollers reduce resistance, making it easier to pull luggage compared to sliding it.
40) What is rolling friction?
Answer: Rolling friction is the resistance to motion when one body rolls over the surface of another. It is smaller than sliding friction and makes rolling easier than sliding.
41) Why is the wheel considered one of the greatest inventions of mankind?
Answer: The wheel reduces friction by enabling rolling instead of sliding, making it easier to move heavy objects and improving efficiency in transportation and machinery.
42) How is rolling friction used in machines?
Answer: Rolling friction is utilized in machines by using ball bearings to reduce sliding friction. Examples include:
Ball bearings between hubs and axles of ceiling fans.
Ball bearings in bicycles.
43) What is the common name for gases and liquids in science?
Answer: The common name for gases and liquids in science is fluids.
44) What force do fluids exert on objects moving through them?
Answer: Fluids exert a frictional force on objects in motion through them.
45) What is the frictional force exerted by fluids called?
Answer: The frictional force exerted by fluids is called drag.
46) On what factors does the frictional force in a fluid depend?
Answer: The frictional force in a fluid depends on:
The speed of the object concerning the fluid.
The shape of the object.
The nature of the fluid.
47) Why do objects lose energy when moving through fluids?
Answer: Objects lose energy when moving through fluids because they have to overcome the frictional force acting on them.
48) How do scientists minimize friction in objects moving through fluids?
Answer: Scientists minimize friction by giving objects special shapes that reduce fluid resistance.
49) Where do scientists get inspiration for designing shapes that reduce fluid friction?
Answer: Scientists get inspiration from nature, as birds and fishes have evolved shapes that help them move efficiently in fluids with less energy loss.
50) Why are birds’ and fishes’ bodies shaped the way they are?
Answer: Birds' and fishes' bodies have evolved into streamlined shapes to help them move through fluids (air and water) efficiently, losing less energy in overcoming friction.
51) How does the shape of an aeroplane relate to nature?
Answer: The shape of an aeroplane is similar to the shape of a bird, as both are designed to reduce fluid friction and move efficiently through air.
52) Why are vehicles designed with special shapes?
Answer: Vehicles are designed with special shapes to reduce fluid friction, allowing them to move more efficiently through air or water.
