Q1. What is a force?

Answer: A force is a push or pull acting on an object arising due to the interaction between objects.

Q2. When does a force come into play?

Answer: A force comes into play when two objects interact with each other.

Q3. Give any two examples of force from daily life.

Answer: Pushing a door to open it and pulling a bucket of water from a well are examples of force.

Q4. Can we see a force? Explain briefly.

Answer: No, we cannot see a force, but we can observe its effects such as a change in shape or motion of an object.

Q5. What are the two main things needed to describe a force completely?

Answer: To describe a force completely, we must know its magnitude (strength) and direction.

Q6. Why is force called a vector quantity?

Answer: Force is called a vector quantity because it has both magnitude and direction.

Q7. What do we mean by “state of motion” of an object?

Answer: The state of motion of an object refers to whether it is at rest or moving and how fast and in what direction it is moving.

Q8. Name the SI unit of force.

Answer: The SI unit of force is the newton (N).

Q9. How can a force change the state of motion of an object?

Answer: A force can start a stationary object, stop a moving object or change the speed of a moving object.

Q10. Can a force change the direction of motion of an object? Give one example.

Answer: Yes. A batsman hitting a moving cricket ball can change its direction using force from the bat.

Q11. How can a force change the shape of an object?

Answer: A force can stretch, compress or bend an object, thus changing its shape, like stretching a rubber band.

Q12. State any two effects of force.

Answer: Force can change the speed of an object and can change its shape or size.

Q13. What happens when two forces act on an object in the same direction?

Answer: When two forces act in the same direction, the net force increases and equals the sum of the two forces.

Q14. What happens when two equal forces act on an object in opposite directions?

Answer: The forces cancel each other and the net force becomes zero, so the state of motion does not change.

Q15. What is a contact force?

Answer: A contact force is a force that acts only when two objects are in physical contact with each other.

Q16. Define muscular force.

Answer: Muscular force is the force exerted by the muscles of our body, such as in lifting, pushing or pulling objects.

Q17. Give one example where animals use muscular force.

Answer: A bullock pulling a cart is an example where the animal uses muscular force to move the cart.

Q18. What is friction?

Answer: Friction is the force that opposes the motion of one surface over another surface in contact.

Q19. Why is friction considered a contact force?

Answer: Friction acts only when two surfaces are in contact, so it is a contact force.

Q20. How does friction help us in walking?

Answer: Friction between our feet and the ground prevents slipping and gives us grip, helping us to walk safely.

Q21. Give one disadvantage of friction.

Answer: Friction causes wear and tear of machine parts and also wastes energy as heat.

Q22. State one method to reduce friction.

Answer: Friction can be reduced by oiling or greasing the moving parts of machines.

Q23. What is a non-contact force?

Answer: A non-contact force is a force that can act between objects without any physical contact between them.

Q24. Give one example of a non-contact force.

Answer: The gravitational force with which the Earth attracts objects towards itself is a non-contact force.

Q25. What is magnetic force?

Answer: Magnetic force is the force exerted by a magnet on another magnet or on magnetic materials like iron.

Q26. Give one example showing magnetic force.

Answer: A magnet attracting iron pins is an example of magnetic force acting at a distance.

Q27. What is electrostatic force?

Answer: Electrostatic force is the force between electrically charged objects, which can attract or repel each other.

Q28. Give one daily life example of electrostatic force.

Answer: A plastic comb rubbed on dry hair attracting small pieces of paper is an example of electrostatic force.

Q29. What is gravitational force?

Answer: Gravitational force is the force of attraction exerted by the Earth (or any mass) on objects towards its centre.

Q30. Why does a stone fall back to the ground when thrown upwards?

Answer: A stone falls back to the ground due to the gravitational force of the Earth pulling it downward.

Q31. What is pressure?

Answer: Pressure is the force acting per unit area of a surface.

Q32. Write the formula for pressure.

Answer: Pressure = Force ÷ Area (P = F / A).

Q33. Name the SI unit of pressure.

Answer: The SI unit of pressure is pascal (Pa).

Q34. How can you increase pressure for the same force?

Answer: For the same force, pressure can be increased by decreasing the area of contact.

Q35. Why do knives and needles have sharp tips?

Answer: They have sharp tips to reduce the area of contact so that the same force produces greater pressure, making cutting or piercing easier.

Q36. Why do porters use a thick cloth pad on their heads while carrying loads?

Answer: A thick cloth pad increases the area of contact and reduces pressure on the head, making it more comfortable to carry loads.

Q37. Why do camels have broad feet?

Answer: Camels have broad feet to increase the area of contact with sand and reduce pressure, so they do not sink into the sand.

Q38. What happens to pressure if force increases but area remains the same?

Answer: If force increases and the area remains the same, the pressure increases.

Q39. What are fluids?

Answer: Fluids are substances that can flow, such as liquids and gases.

Q40. Do liquids exert pressure? If yes, in which directions?

Answer: Yes, liquids exert pressure on the walls and bottom of the container and in all directions.

Q41. How does pressure in a liquid change with depth?

Answer: Pressure in a liquid increases with depth; the deeper you go, the greater the pressure.

Q42. Why are dams built thicker at the bottom than at the top?

Answer: Dams are thicker at the bottom to withstand the higher water pressure at greater depths.

Q43. How is gas pressure produced in a container?

Answer: Gas pressure is produced by continuous collisions of gas molecules with the walls of the container.

Q44. Give one example where gas pressure is used in daily life.

Answer: The air pressure inside a bicycle tyre helps it stay firm and support the weight of the rider.

Q45. What is atmosphere?

Answer: The atmosphere is the layer of air surrounding the Earth.

Q46. What is atmospheric pressure?

Answer: Atmospheric pressure is the pressure exerted by the air column of the atmosphere on the Earth’s surface and on all objects.

Q47. Why are we not crushed under atmospheric pressure?

Answer: We are not crushed because the pressure inside our body (from blood and body fluids) balances the atmospheric pressure outside.

Q48. How does a drinking straw work?

Answer: When we suck air from the straw, the air pressure inside it decreases and atmospheric pressure on the liquid surface pushes the liquid up into the straw.

Q49. How does a syringe fill with liquid?

Answer: Pulling the plunger increases space and lowers pressure inside the syringe, so atmospheric pressure pushes the liquid into it.

Q50. Give one use of atmospheric pressure in everyday objects.

Answer: Suction cups or suction hooks stick to smooth surfaces due to atmospheric pressure acting on them from outside.