SEBA Class 8 Science Chapter 7 Friction Solutions English Medium to each chapter is provided in the list so that you can easily browse through different chapters SEBA Class 8 Science Chapter 7 Friction Question Answer and select need one. SEBA Class 8 Science Chapter 7 Friction Solutions Download PDF. SEBA Class 8 Science Texbook Solutions English Medium.
SEBA Class 8 Science Chapter 7 Friction
Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. SEBA Class 8 General Science Textual Solutions in English are part of All Subject Solutions. Here we have given Class 8 Science Textbook Question Answer, SEBA Class 8 Science English Medium Textbook Solutions for All Chapters, You can practice these here.
Friction
Chapter: 7
PART – I
EXERCISE
1. Fill in the blanks:
(a) Friction opposes the __________ between the surfaces in contact with each other.
Ans: Friction opposes the motion between the surfaces in contact with each other.
(b) Friction depends on the _________ of surfaces.
Ans: Friction depends on the nature of surfaces.
(c) Friction produces ____________.
Ans: Friction produces heat.
(d) Sprinkling of powder on the carrom board ___________ friction.
Ans: Sprinkling of powder on the carrom board reduces friction.
(e) Sliding friction is ________ than the static friction.
Ans: Sliding friction is less than the static friction.
2. Four children were asked to arrange forces due to rolling, static and sliding frictions in a 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.
Ans: (c) Static, sliding, rolling.
3. Alida runs her toy car on 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 and 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.
Ans: (a) Wet marble floor, dry marble floor, newspaper and towel.
Explanation:
(a) Wet marble floor offers the least friction (slippery surface).
(b) Dry marble floor has slightly more friction than wet marble.
(c) Newspaper adds more roughness and thus more friction.
(d) Towel has the roughest texture, hence offers the maximum friction.
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.
Ans: When the writing desk is tilted and the book starts sliding down, the force of gravity pulls the book downward along the slope. However, frictional force always acts in the opposite direction of motion. Since the book is sliding downward, the frictional force acts upward, along the surface of the desk, opposing the motion. This friction tries to stop or slow down the sliding of the book. The smoother the surface, the lesser the friction, and the faster the book slides. The rougher the surface, the greater the friction, and the slower the book’s motion down the slope.
5. You spill a bucket of soapy water on a marble floor accidently. Would it make it easier or more difficult for you to walk on the floor? Why?
Ans: If you spill a bucket of soapy water on a marble floor, it would make it more difficult to walk on the floor.
Reason:
Soapy water reduces the friction between your feet and the floor. Friction is the force that helps us walk by providing grip. When friction decreases, the floor becomes slippery, and it becomes hard to maintain balance while walking. As a result, you may slip and fall. Therefore, the presence of soapy water lowers the friction, making it difficult and unsafe to walk on the marble floor.
6. Explain why sportsmen use shoes with spikes.
Ans: Sportsmen wear shoes with spikes to increase the friction between their shoes and the ground. While running or playing, they need a strong grip so that they do not slip and can move quickly and safely. The spikes dig into the ground, which increases the surface contact and provides better grip. This helps the player to run faster, stop suddenly, or change direction without falling. On smooth or wet surfaces, friction is low, and the risk of slipping is high. Spiked shoes solve this problem by increasing friction and giving the sportsman more control during the game.
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?
Ans: Seema will have to apply a larger force than Iqbal because she is pushing a heavier box. The force of friction between an object and the floor depends on the weight of the object. A heavier object presses more firmly against the surface, which increases the frictional force. As a result, more effort is required to move it. Since Seema’s box is heavier, the friction between the box and the floor is greater compared to Iqbal’s lighter box. Therefore, Seema has to apply a greater force to overcome the higher friction and move the heavier box forward.
8. Explain why sliding friction is less than static friction.
Ans: When an object is not moving, it sticks more strongly to the surface. This is called static friction, and it is strong.
When the object starts moving, it slides over the surface. The contact between the two surfaces becomes less. This is called sliding friction, and it is weaker.
So, sliding friction is less than static friction because it is easier to keep an object moving than to start moving it.
9. Give examples to show that friction is both a friend and a foe.
Ans: (i) Matchstick lights up when struck against the rough surface — friction helps produce heat.
(ii) Brakes work in bicycles, motorcycles, and cars because friction slows down the wheels.
(iii) Nails and screws stay fixed in walls or wood because friction holds them in place.
Friction as a Foe (Harmful):
(a) Machine parts wear out quickly due to continuous rubbing (friction).
(b) Overheating in engines happens because friction produces unwanted heat.
(c) Extra fuel is used in vehicles to overcome friction which reduces mileage.
10. Explain why objects moving in fluids must have special shapes.
Ans: Friction is a natural force that resists motion, and fluid friction (drag) can be a big challenge for anything moving through air or water. To overcome this, nature has gifted animals like birds and fish with streamlined bodies that help them move easily. Humans have applied the same idea in the design of vehicles like airplanes, boats, and cars.
So, the special streamlined shape is not just a design choice it is essential for efficient movement in fluids. It helps save energy, improves speed, and ensures smooth motion.
Therefore, we can say that objects moving in fluids must have special shapes to overcome the frictional force of the fluid and to move smoothly and efficiently.
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