GSEB Class 8 Science Solutions Chapter 12 Friction

Question 1. Fill in the blanks:
(a) Friction opposes __________ between the surfaces in contact with each other.
(b) Friction depends on the __________ of surfaces.
(c) Friction produces __________.
(d) A sprinkling of powder on the carrom board __________ friction.
(e) Sliding friction is __________ than static friction.
Answer:
(a) relative motion
(b) nature
(c) heat
(d) reduces
(e) less.
In simple words: Friction works against things moving against each other. How much friction there is depends on what the surfaces are like. When things rub, friction makes heat. Putting powder on a carrom board makes less friction. Sliding friction is always smaller than static friction.

Exam Tip: For fill-in-the-blanks, always use precise scientific terms as answers.

Question 2. Four children were asked to arrange forces due to rolling, static, and sliding frictions in decreasing order. Their arrangements are given below. Choose the correct arrangement:
(a) rolling, static, sliding
(b) rolling, sliding, static
(c) static, sliding, rolling
(d) sliding, static, rolling
Answer: (c) Static, sliding, rolling.
In simple words: Static friction is the greatest, then comes sliding friction, and rolling friction is the smallest.

Exam Tip: Remember the order of friction types: static > sliding > rolling.

Question 3. Alida runs her toy car on a dry marble floor, wet marble floor, newspaper, and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be
(a) wet marble floor, dry marble floor, newspaper, towel.
(b) newspaper, towel, dry marble floor, wet marble floor.
(c) towel, newspaper, dry marble floor, wet marble floor.
(d) wet marble floor, dry marble floor, towel, newspaper.
Answer: (a) wet marble floor, dry marble floor, newspaper, towel.
In simple words: The car will move easiest on the wet marble floor because it has the least friction. It will be hardest to move on the towel because it has the most friction.

Exam Tip: The smoother and wetter a surface is, the less friction it will have. Rougher, drier surfaces have more friction.

Question 4. Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
Answer: The book moves downwards. The frictional force acts opposite to the movement of the book. So, it acts upwards.

In simple words: When the book slides down the tilted desk, the friction force always pushes upwards against its movement.

Exam Tip: Frictional force always acts in the opposite direction to the motion or intended motion of an object.

Question 5. You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?
Answer: The layer of soap makes the floor very smooth, which lowers the friction. This means your foot cannot get a good hold on the ground. So, it becomes hard to walk on the soapy floor, and you might start to slip.
In simple words: It becomes harder to walk because soap makes the floor very smooth, reducing friction and making it difficult for your feet to grip.

Exam Tip: Less friction makes walking difficult because our feet need friction to push against the ground and move forward without slipping.

Question 6. Explain why sportsmen use shoes with spikes.
Answer: Athletes wear special shoes with spikes to boost the friction between their footwear and the ground. This extra grip helps them avoid slipping when they run or play.
In simple words: Sportsmen wear shoes with spikes to get more friction, which stops them from slipping while running or playing.

Exam Tip: Spikes or treads on shoes are designed to increase friction, providing better grip and preventing falls during activities.

Question 7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
Answer: The heavier object presses down more strongly against the floor, which causes more friction. Because of this extra friction, Seema will need to use a bigger force to move her heavier box.
In simple words: Seema will need to use more force because her box is heavier. Heavier objects create more friction as they press harder against the ground.

Exam Tip: The force of friction is generally greater for heavier objects because they exert a greater normal force on the surface.

Question 8. Explain why sliding friction is less than static friction.
Answer: When two objects are sliding, their rough surfaces don't have enough time to interlock or get stuck together properly. Because of this, they experience less resistance. That's why sliding friction is always smaller than static friction.
In simple words: Sliding friction is less than static friction because surfaces have less time to catch onto each other when moving, compared to when they are still.

Exam Tip: Static friction must be overcome to start movement, while sliding friction acts once an object is already in motion. It takes less force to keep an object sliding than to start it moving.

Question 9. Give examples to show that friction is both a friend and a foe.
Answer: Examples to show that friction is a friend and a foe:
Friction is a friend:
1. Friction helps us to hold and grab various items.
2. It permits us to walk easily on different surfaces.
3. It assists in slowing down or stopping objects that are moving.
4. It enables us to write on paper or a blackboard.
5. Objects stay in their position because of the rubbing force between surfaces.
Friction is a foe:
1. Friction causes objects to wear down and get damaged.
2. It damages various parts inside machines.
3. Machines and tools need regular upkeep, which wastes a lot of money.
4. It decreases the pace of moving things, so more effort is needed.
5. It stops objects from moving freely.
In simple words: Friction is helpful because it lets us grip things, walk, stop moving objects, and write. But it's also harmful because it causes things to wear out, damages machines, requires costly maintenance, slows things down, and prevents smooth movement.

Exam Tip: When asked for examples, try to provide a balanced list for both positive (friend) and negative (foe) aspects.

Question 10. Explain why objects moving in fluids must have special shapes.
Answer: Objects that move through liquids or gases need a particular shape. This unique shape is known as a streamlined shape. A streamlined design assists in reducing the drag or friction between the object and the fluid. These objects typically have pointed front ends, a slightly wider middle, and then narrow down at the back.
In simple words: Objects moving in liquids or air need a special streamlined shape. This shape helps them cut through the fluid easily and reduce friction, usually with a pointed front and a tapered back.

Exam Tip: Streamlining is crucial for vehicles (cars, planes, boats) to reduce air or water resistance and improve efficiency.