"Force and Pressure" for Class 8 Science CBSE:-
Extra 30 short questions and answers from the chapter:8
1. What is force?
Ans: A force is a push or pull acting on an object that can change its state of motion, direction, or shape. It is measured in Newtons (N).
2. What are the effects of force?
Ans: A force can:
Change the speed of an object.
Change the direction of motion.
Change the shape of an object.
3. What is the SI unit of force?
Ans: The SI unit of force is Newton (N). One Newton is the force required to accelerate a 1 kg mass by 1 m/s².
4. Name two types of forces with examples.
Ans:
Contact Force – Example: Frictional force, Muscular force.
Non-Contact Force – Example: Gravitational force, Magnetic force.
5. What is frictional force?
Ans: Frictional force is the force that opposes the motion of an object when it moves over a surface. Example: A ball rolling on the ground slows down due to friction.
6. Define pressure and give its formula.
Ans: Pressure is the force applied per unit area. It is given by the formula:
Pressure= force per unit area
SI unit: Pascal (Pa).
7. Why do sharp knives cut better than blunt knives?
Ans: A sharp knife has a smaller surface area, which increases the pressure for the same applied force, making cutting easier.
8. What is gravitational force?
Ans: Gravitational force is the force of attraction exerted by the Earth on all objects, pulling them toward its centre. Example: A ball falls when dropped.
9. Why do camels have broad feet?
Ans: Broad feet increase the surface area, reducing pressure on the sand, preventing camels from sinking.
10. What is a non-contact force? Give an example.
Ans: A non-contact force is a force that acts without direct physical contact. Example: Magnetic force – A magnet attracts iron from a distance.
11. Why does a car stop when brakes are applied?
Ans: The frictional force between the brake pads and wheels opposes the motion and gradually stops the car.
12. How do liquids exert pressure?
Ans: Liquids exert pressure in all directions. This is observed when water leaks equally from multiple holes in a bottle.
13. How does pressure vary with depth in a liquid?
Ans: Pressure increases with depth. Example: The deeper you dive in a swimming pool, the more pressure you feel.
14. What is atmospheric pressure?
Ans: The air around us exerts pressure due to its weight, called atmospheric pressure. It is measured by a barometer.
15. Why do deep-sea divers wear special suits?
Ans: Deep-sea divers experience high water pressure at great depths. Special suits help withstand this pressure.
16. What happens to atmospheric pressure as we move up a mountain?
Ans: Atmospheric pressure decreases with altitude because the weight of air above decreases.
17. Why does a rubber sucker stick to a smooth surface?
Ans: When pressed, air inside the sucker is removed, creating a low-pressure region. The higher external air pressure holds it in place.
18. Why is it difficult to walk on sand?
Ans: Sand has a larger surface area, reducing pressure, making it difficult to push against the ground.
19. What is muscular force? Give an example.
Ans: Muscular force is the force exerted by the muscles of the body. Example: Lifting a book.
20. Why are school bags provided with broad straps?
Ans: Broad straps increase the surface area, reducing the pressure on the shoulders, making it comfortable to carry heavy loads.
21. What happens when air is removed from a sealed can?
Ans: The external atmospheric pressure crushes the can, as there is no internal air to balance it.
22. Why does a straw work when drinking juice?
Ans: Sucking the straw reduces air pressure inside it, so the higher atmospheric pressure pushes the juice up into the mouth.
23. Why do people living in high altitudes experience difficulty in breathing?
Ans: At high altitudes, atmospheric pressure is lower, reducing oxygen levels, making breathing difficult.
24. Why do astronauts wear pressurized suits?
Ans: In space, there is no atmospheric pressure. Pressurized suits prevent the body from expanding due to the lack of external pressure.
25. Why do train wheels produce sparks when stopping suddenly?
Ans: The friction between the wheels and tracks generates heat, causing sparks.
26. Why do vehicles have grooved tires?
Ans: Grooves increase friction between the tire and the road, preventing slipping.
27. Why does a ball stop rolling after some time?
Ans: Due to frictional force between the ball and the ground, which slows it down and eventually stops it.
28. What is the role of friction in everyday life?
Ans: Friction helps in:
Walking without slipping.
Holding objects.
Stopping vehicles when brakes are applied.
29. How does an increase in surface area affect pressure?
Ans: Increasing surface area reduces pressure. Example: A wide wooden plank on soft ground prevents sinking.
30. Why is atmospheric pressure not felt by humans?
Ans: The pressure inside our body balances the external atmospheric pressure, so we do not feel it.
