"Force and Pressure" for Class 8 Science CBSE:-
Extra 20 important long questions and answers from the chapter:8
1. What is force? Explain different types of forces.
Ans: Force is a push or pull acting on an object that can change its motion, direction, or shape. It is measured in Newton (N).
Types of forces:
Contact Forces – Forces that act when objects are in direct contact.
Muscular force – Applied by muscles (e.g., lifting a book).
Frictional force – Opposes motion (e.g., rubbing hands together).
Non-Contact Forces – Forces that act from a distance.
Gravitational force – Pulls objects toward Earth (e.g., falling objects).
Magnetic force – Attraction/repulsion between magnets.
Electrostatic force – Force due to electric charges.
2. What are the effects of force on an object?
Ans: A force applied to an object can:
Change its state of motion – A stationary object may start moving.
Change its speed – A moving object can speed up or slow down.
Change its direction – A force can make an object move in a different direction.
Change its shape – Squeezing clay changes its shape.
Stop a moving object – Applying brakes stops a moving vehicle.
Overcome friction – Pushing a heavy box requires force to overcome friction.
3. What is friction? How is it useful and harmful?
Ans: Friction is the force that opposes the motion of an object when it moves over a surface.
Useful effects of friction:
Helps us walk – Prevents slipping.
Enables writing – Provides grip on paper.
Stops moving vehicles – Brakes use friction.
Holds objects together – Screws and nails stay in place due to friction.
Creates heat – Used in matchsticks to produce fire.
Harmful effects of friction:
Causes wear and tear – Machines and shoes wear out.
Reduces efficiency – Extra energy is needed to overcome friction.
Generates unwanted heat – Overheating in engines.
Slows down motion – Makes movement difficult in some cases.
4. Explain the term "pressure" and give examples.
Ans: Pressure is the force applied per unit area.
Pressure=force per unit area
Examples:
Knives have sharp edges – Reducing area increases pressure, making cutting easier.
School bags have broad straps – Increases area, reducing pressure on shoulders.
Camels have broad feet – Prevents sinking in sand by reducing pressure.
Tractors have large tires – Reduces pressure on soft soil.
High heels exert more pressure – Small area leads to higher pressure.
5. How does pressure vary in liquids?
Ans:
Liquids exert pressure in all directions – Water leaks from all holes in a bottle.
Pressure increases with depth – A diver feels more pressure deeper underwater.
Depends on the height of the liquid column – Higher the liquid, greater the pressure.
Acts perpendicular to surfaces – Pressure acts at right angles to container walls.
Independent of shape – Pressure at the same depth is equal in any container.
6. What is atmospheric pressure? How does it affect us?
Ans: Atmospheric pressure is the pressure exerted by air on everything on Earth.
Effects:
We don’t feel it – The pressure inside our body balances it.
Syringes and straws work – Removing air creates lower pressure, and liquid is pushed in.
Suction cups stick to walls – Air inside is removed, and higher external pressure holds it.
Airplane passengers feel discomfort – Less atmospheric pressure at high altitudes affects breathing.
Boiling point changes – Water boils at a lower temperature in mountains due to lower pressure.
7. Explain how friction can be increased and decreased.
Ans:
To increase friction:
Make surfaces rough – Adding sand to slippery roads.
Use grooved tires – Provides better grip.
Apply more force – Pressing objects together increases friction.
Use friction-enhancing materials – Rubber grips, textured gloves.
To decrease friction:
Make surfaces smooth – Polishing floors.
Use lubricants – Oil in machines reduces friction.
Use ball bearings – Reduce contact between moving parts.
Use streamlined shapes – Reduces air and water resistance in vehicles.
8. Why is it easier to walk on a rough surface than on a smooth one?
Ans:
Rough surfaces provide more friction, preventing slipping.
Smooth surfaces reduce friction, making walking difficult.
Friction helps in getting a better grip.
Walking on ice is difficult due to low friction.
Rubber soles increase friction for better walking.
9. How does pressure affect deep-sea divers and astronauts?
Ans:
Deep-sea divers experience high water pressure, requiring special suits.
Scuba tanks help divers breathe underwater.
Astronauts face low pressure in space, needing pressurized suits.
Low pressure at high altitudes causes breathing problems.
Special equipment is used to regulate pressure in submarines and spacecraft.
10. How does a hydraulic system work?
Ans:
Hydraulic systems use liquids to transmit pressure.
Pressure applied at one point is transmitted equally throughout the liquid.
Used in hydraulic brakes, jacks, and lifts.
Follows Pascal’s Law – "Pressure in a confined liquid is transmitted equally in all directions."
Helps lift heavy loads with small force.
11. Explain why pressure is more in a liquid at greater depth.
Ans:
Liquids exert pressure in all directions – The deeper you go, the more pressure you experience.
Pressure increases with depth because the weight of the water above increases.
Example: Dams are thicker at the bottom to withstand high pressure.
Water at greater depth exerts more force on submerged objects.
Deep-sea divers wear special suits to withstand high pressure.
12. Why do gases exert pressure in all directions?
Ans:
Gas molecules move randomly and collide with container walls.
These collisions create pressure on all sides.
Example: Inflated balloons expand equally in all directions.
If a balloon is pricked, air rushes out due to high internal pressure.
Atmospheric pressure exists because of gas molecules in the air.
Gas pressure is used in air pumps, spray cans, and air brakes.
13. Why do astronauts experience weightlessness in space?
Ans:
Weightlessness occurs because there is no significant gravitational force acting on them.
In space, astronauts are in free fall, meaning they are continuously falling around Earth.
There is no force acting opposite to gravity to create a normal weight sensation.
This makes objects float inside a spacecraft.
On the Moon, gravity is 1/6th of Earth's, so astronauts feel lighter.
Special training is given to astronauts to adjust to weightlessness.
14. Why do deep-sea fish die when brought to the surface?
Ans:
Deep-sea fish live under high water pressure.
Their bodies are adapted to withstand high pressure.
When brought to the surface, the external pressure decreases suddenly.
Their internal pressure remains high, causing body expansion or organ damage.
This can lead to the rupture of their swim bladders.
Special pressurized tanks are used to keep deep-sea creatures alive.
15. How does a suction cup stick to a surface?
Ans:
When pressed, air inside the suction cup is removed.
This creates a low-pressure area inside the cup.
The higher external atmospheric pressure pushes the cup against the surface.
The cup remains stuck until air is allowed back inside.
Used in wall hooks, car phone holders, and suction toys.
Works best on smooth surfaces like glass.
16. Explain the working of a hydraulic brake.
Ans:
Hydraulic brakes work on Pascal’s Law.
When a driver presses the brake pedal, a small force is applied to the brake fluid.
The fluid transmits the pressure equally to all connected brake pads.
The pads press against the wheels, stopping the vehicle.
The system allows small effort to create a large stopping force.
Found in cars, buses, and trucks.
17. Why do sharp objects exert more pressure than blunt objects?
Ans:
Pressure is inversely proportional to area:
A sharp knife has a small area, so it applies greater pressure for the same force.
This makes cutting easier.
Blunt knives spread the force over a larger area, reducing pressure and making cutting harder.
High heels exert more pressure than flat shoes due to small contact area.
Used in needles, nails, and scissors.
18. Why do mountaineers carry oxygen cylinders while climbing high altitudes?
Ans:
At high altitudes, atmospheric pressure decreases.
This leads to lower oxygen levels in the air.
Breathing becomes difficult, leading to altitude sickness.
Oxygen cylinders provide a steady oxygen supply.
Symptoms of altitude sickness include dizziness, headache, and nausea.
Special training is given to climbers to adapt to low-pressure environments.
19. How does pressure help in filling a syringe?
Ans:
When the plunger is pulled back, it reduces pressure inside the syringe.
The higher atmospheric pressure outside pushes the liquid into the syringe.
When the plunger is pressed, liquid is forced out due to increased pressure.
Used in vaccinations, medical injections, and fuel injectors.
The process follows the principle of fluid pressure.
If the needle is blocked, high pressure may damage the syringe.
20. How does pressure work in a spray can?
Ans:
Spray cans contain liquid under high pressure.
When the nozzle is pressed, a small opening releases the liquid.
The higher internal pressure forces the liquid out as a fine mist.
Atmospheric pressure outside helps spread the spray evenly.
Used in perfumes, deodorants, insect repellents, and paints.
If a can is punctured or heated, it can explode due to sudden pressure release.
