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Q1. Pressure exerted by a block is maximum when
Pressure is defined as force per unit area (P = F/A). For a given force (weight of the block), pressure is inversely proportional to the area. This means that if the area is smaller, the pressure is greater. For example, a block standing on its narrow edge exerts more pressure than when lying flat because the area of contact is smaller. This is why sharp objects like nails and knives have small areas to increase pressure.
Q2. Buoyancy is experienced by objects when they are immersed in
Buoyancy is the upward force experienced by objects when they are immersed in fluids. Fluids include both liquids (like water) and gases (like air). When an object is placed in a fluid, the fluid exerts an upward force called buoyant force. This is why objects feel lighter in water and why ships float. Buoyancy does not occur in solids or in a vacuum because there is no fluid to exert the upward force.
Q3. A floating object rises because
For an object to float, the upward buoyant force exerted by the fluid must be greater than or equal to the downward weight of the object. When the buoyant force is greater than the weight, the object rises to the surface and floats. This happens when the object displaces enough fluid to create a buoyant force that can support its weight. Gravity is still present; it is the weight that is being balanced.
Q4. The force due to gravity always acts
The force due to gravity (weight) always acts vertically downward towards the centre of the Earth. This is a constant direction for all objects on Earth. It does not act upward, horizontally, or randomly. The downward direction of gravity is what causes objects to fall when dropped and is the force that creates weight. This downward force is balanced by the upward normal force when an object is at rest on a surface.
Q5. Lying on sand exerts less pressure because
When you lie down on sand, your body is spread over a larger area. Since pressure = force/area, increasing the area decreases the pressure for the same force (your weight). This is why lying on sand does not sink you in as much as standing on sand, where the area of contact is much smaller (only your feet). The weight (thrust) remains the same; only the area changes, reducing the pressure.
Q6. The same force acting on a larger area produces
Pressure is inversely proportional to area (P = F/A). For a constant force, if the area increases, the pressure decreases. This is why wide tyres on heavy vehicles reduce the pressure on the road, preventing damage. Similarly, snowshoes have large areas to reduce pressure and prevent sinking into soft snow. The force remains the same, but spreading it over a larger area reduces the effect of the force.
Q7. The SI unit of pressure is
The SI unit of pressure is the pascal (Pa), named after Blaise Pascal. One pascal is defined as one newton per square metre (1 Pa = 1 N/m²). Newton is the unit of force, watt is the unit of power, and joule is the unit of work and energy. The pascal is a smaller unit, so larger pressures are often expressed in kilopascals (kPa) or megapascals (MPa).
Q8. The effect of thrust depends on
Thrust is the force acting perpendicular to a surface. The effect or pressure produced by a given thrust depends on the area over which it is applied. The same force applied over a smaller area produces greater pressure and more effect. For example, a sharp knife cuts better than a blunt one because the force is concentrated over a smaller area. So the effect of thrust depends on the area, not just the force.
Q9. Pressure is defined as
Pressure is defined as the thrust (force acting perpendicular to a surface) divided by the area over which it acts. The formula is P = F/A, where P is pressure, F is thrust or force, and A is area. This definition tells us that pressure is the force per unit area. A larger force or a smaller area results in greater pressure.
Q10. Which quantity changes when the area changes?
When the area changes while the force (thrust or weight) remains constant, the pressure changes. Mass and weight are properties of the object and do not change when the area changes. Thrust is the force itself and also does not change. Only pressure changes because it depends on both force and area. For the same force, a larger area gives smaller pressure, and a smaller area gives larger pressure.
Q11. A nail has a pointed tip to
A nail has a pointed tip with a very small area. When a force is applied, this small area concentrates the force, producing a very large pressure. According to P = F/A, reducing the area increases the pressure for the same force. This high pressure allows the nail to penetrate into wood or other materials. This is the same principle used in knives, needles, and other sharp objects—they have small areas to increase pressure.
Q12. Buoyant force acts in
The buoyant force always acts in the upward direction, opposite to the weight of the object. This upward force is exerted by the fluid on the object. It is this upward force that makes objects feel lighter in water and allows objects to float. The buoyant force is due to the pressure difference between the bottom and top of the immersed object, with greater pressure at the bottom pushing upward.
Q13. Liquids and gases are together called
Liquids and gases are together called fluids because they can flow and take the shape of their containers. Both liquids and gases are fluids because their particles can move freely past each other. This property is important for understanding buoyancy and pressure, as fluids exert pressure in all directions. Plasma is a different state of matter, and solids have fixed shapes.
Q14. A completely immersed object will float if
For a completely immersed object to float to the surface, the buoyant force must be greater than its weight. When this happens, there is a net upward force that pushes the object up. If the buoyant force equals the weight, the object will remain suspended in the fluid. If the weight is greater, the object will sink. Floating occurs when the buoyant force is greater than or equal to the weight.
Q15. When swimming in water, a person feels lighter because of
When a person swims in water, they feel lighter because of the buoyant force exerted by the water on their body. The water pushes upward against the person, partially supporting their weight. This reduces the effective weight and makes them feel lighter. This same principle allows people to float and swim. Gravity still acts downward, but the buoyant force reduces the net downward force.
Q16. Pressure in a confined fluid is transmitted
According to Pascal’s law, pressure applied to a confined fluid is transmitted undiminished in all directions. This means that if you apply pressure at one point in a fluid, it is transmitted equally to all parts of the fluid. This principle is used in hydraulic systems, such as car brakes and hydraulic lifts, where a small force applied at one point can produce a large force at another point.
Q17. The upward force exerted by a fluid is called
The upward force exerted by a fluid on an object immersed in it is called the buoyant force. This force is also known as upthrust. It is the force that makes objects feel lighter in water and allows them to float. Pressure is the force per unit area, thrust is the force perpendicular to a surface, and weight is the downward force due to gravity.
Q18. The reason a sheet of iron sinks is
A sheet of iron sinks because the buoyant force acting on it is less than its weight. The buoyant force depends on the volume of fluid displaced. Since iron is denser than water, it displaces a volume of water whose weight is less than the weight of the iron. As a result, the buoyant force is insufficient to support the weight, and the sheet sinks. This is why heavy materials like iron sink, while lighter or hollow materials float.
Q19. Buoyant force depends on
The buoyant force depends on the density of the fluid and the volume of fluid displaced. According to Archimedes’ principle, the buoyant force is equal to the weight of the fluid displaced, which depends on the density of the fluid. A denser fluid (like salt water) exerts a greater buoyant force than a less dense fluid (like fresh water). The mass or shape of the object does not directly determine the buoyant force; only the volume displaced and fluid density matter.
Q20. A solid exerts pressure due to its
A solid exerts pressure on the surface below it due to its weight. The pressure is the force (weight) divided by the area of contact. The weight of the solid is the downward force due to gravity. The shape and density affect the weight, but the direct cause of pressure is the weight (force) acting on the area. The formula P = F/A shows that the force (weight) creates the pressure.
Q21. The force acting on sand while standing is equal to
The force acting on the sand when a person stands on it is the weight of the person. This is the downward force exerted by the person on the sand. The weight is equal to the mass of the person multiplied by the acceleration due to gravity (W = mg). The pressure on the sand depends on this force divided by the area of the feet. The force itself is the weight, not the mass or area.
Q22. Buoyancy explains why objects
Buoyancy is the phenomenon that explains why some objects float while others sink in a fluid. The principle of buoyancy, first described by Archimedes, explains that an object will float if it displaces a volume of fluid whose weight is greater than or equal to the object’s weight. If the object’s weight is greater, it sinks. So buoyancy directly explains the behaviour of objects in fluids—whether they sink or float.
Q23. Pressure is measured in
Pressure is measured in newtons per square metre (N/m²), which is also called a pascal (Pa). Since pressure is force divided by area (P = F/A), the unit is the unit of force (newton) divided by the unit of area (square metre). This gives N/m². Newton (N) is the unit of force, kg/m² is not a standard pressure unit, and m/s² is the unit of acceleration.
Q24. To keep an object completely immersed, an external force must act
To keep an object completely immersed in a fluid, an external force must act downward. This is because the buoyant force acts upward and may be greater than the weight of the object. If the buoyant force is greater, the object would rise. To prevent it from rising, a downward force must be applied to keep it submerged. This is why you need to push a floating object down to fully immerse it.
Q25. A plastic bottle floats because
A plastic bottle floats because the buoyant force exerted by the water on it is greater than its weight. The bottle displaces a volume of water whose weight is greater than the weight of the bottle. As a result, there is a net upward force, and the bottle floats. This happens because the bottle is less dense than water. The buoyant force supports the bottle’s weight.
Q26. Thrust per unit area is called
Thrust per unit area is defined as pressure. The formula is P = F/A, where P is pressure, F is thrust (force acting perpendicular to a surface), and A is the area over which the force acts. This is the fundamental definition of pressure. Weight is the force of gravity, force is the push or pull, and density is mass per unit volume.
Q27. Buildings have wide foundations to
Buildings have wide foundations to reduce the pressure they exert on the ground. The weight of the building is large, so if this weight were concentrated on a small area, the pressure would be very high and the building might sink into the ground. By spreading the weight over a larger area (wide foundation), the pressure is reduced. This is done to prevent the building from sinking or causing damage to the ground.
Q28. Which quantity remains same when a block is placed on different sides?
When a block is placed on different sides, the thrust (force) remains the same because the weight of the block is constant regardless of which side it rests on. However, the area of contact changes depending on which side is down. As a result, the pressure changes because pressure depends on the area. The surface in contact also changes. So the quantity that remains the same is the thrust (weight).
Q29. Standing on sand exerts more pressure because
When you stand, your feet have a small area of contact with the sand. The pressure is force divided by area. For the same force (your weight), a smaller area gives higher pressure. This is why your feet sink into sand when you stand but sink less when you lie down (larger area). The thrust remains the same; only the area changes, increasing the pressure.
Q30. In standing and lying positions, thrust is
Thrust is the force acting perpendicular to a surface. In both standing and lying positions, the force exerted by the person on the ground is equal to their weight. Weight does not change based on position, so the thrust (force) is the same in both positions. However, the pressure changes because the area of contact changes—standing has less area (more pressure), lying has more area (less pressure).
Q31. Another name for buoyant force is
Buoyant force is also called upthrust. It is the upward force exerted by a fluid on an object immersed in it. The term “upthrust” describes the direction of the force—it pushes objects upward. Drag is a force opposing motion through a fluid, thrust is the force perpendicular to a surface, and pressure is force per unit area. So upthrust is the correct term.
Q32. The SI unit of pressure is named after
The SI unit of pressure is named after Blaise Pascal, a French mathematician and physicist who made important contributions to the study of fluids and pressure. The unit is called the pascal (Pa). Newton is the unit of force, and Archimedes and Galileo are famous scientists but have no units named after them for pressure.
Q33. Weight of an object acts in which direction?
The weight of an object is the force of gravity acting on it. It always acts vertically downward, towards the centre of the Earth. This is the direction in which objects fall when dropped. The weight is directed downward regardless of the object’s position or motion. It does not act sideways, upward, or randomly.
Q34. The force acting perpendicular to a surface is called
The force acting perpendicular to a surface is called thrust. It is the force that is applied normally (at 90 degrees) to the surface. For example, when you push a wall, the force applied perpendicular to the wall is the thrust. Weight is a specific type of thrust (acting vertically downward), buoyancy is the upward force in fluids, and pressure is thrust per unit area. So thrust is the correct term for the force perpendicular to a surface.
Q35. The same force acting on a smaller area produces
For the same force, a smaller area produces more pressure because pressure = force/area. This is why sharp objects (with small area) exert more pressure and can cut or pierce. For example, a needle with a very small tip can penetrate fabric easily because the force is concentrated over a tiny area, creating high pressure.
Q36. When a person stands on loose sand, the force acting on sand is
When a person stands on loose sand, the force acting on the sand is the thrust, which is the weight of the person acting perpendicular to the sand surface. This thrust is what causes the sand to compress and the feet to sink. Pressure is the effect of this thrust divided by the area, friction opposes motion, and buoyancy is the upward force in fluids. So thrust is the correct term for the force.
Q37. When an object is immersed in water, it experiences
When an object is immersed in water, it experiences both upward and downward forces. The downward force is its weight due to gravity. The upward force is the buoyant force exerted by the water. The net force determines whether the object sinks, floats, or remains suspended. If the buoyant force is greater, the object rises; if weight is greater, it sinks.
Q38. The weight of an object acts
The weight of an object always acts vertically downward, towards the centre of the Earth. This is the direction of the gravitational force. It acts downward regardless of the object’s location or the presence of other forces. The weight does not act horizontally, upward, or randomly—it is always directed downward.
Q39. A bucket of water feels heavier when taken out because
When a bucket is in water, it experiences an upward buoyant force from the water, which supports some of its weight and makes it feel lighter. When the bucket is taken out of the water, this buoyant force is no longer present (or is reduced to just air buoyancy, which is negligible). As a result, the full weight of the bucket is felt, making it seem heavier. The actual weight hasn’t changed; the buoyant force has decreased.
Q40. Fluids exert pressure on
Fluids exert pressure on all surfaces in contact with them—both the base (bottom) and the walls (sides) of the container. This is because fluid pressure acts in all directions. At any point in a fluid, pressure is exerted equally in all directions. This is why the bottom and sides of a water tank experience pressure, and this pressure increases with depth.
Q41. Pressure exerted by a block is minimum when
Pressure is minimum when the area of contact is largest because pressure is inversely proportional to area (P = F/A). For the same force (weight), a larger area gives smaller pressure. This is why lying down on sand (larger area) exerts less pressure than standing (smaller area). So the block exerts minimum pressure when it rests on its largest face.
Q42. The thrust exerted by a wooden block is equal to its
The thrust exerted by a wooden block on a surface is the force it applies perpendicular to the surface. This force is equal to the weight of the block (mg). The area affects the pressure but not the thrust. The thrust is simply the force, which for a block at rest on a horizontal surface is equal to its weight. Pressure is thrust divided by area, so it is different.
Q43. When released, a floating bottle moves
When a floating bottle is pushed down and then released, it moves upward because the buoyant force is greater than its weight. This net upward force causes the bottle to rise until it reaches the surface where it floats. If the bottle is already floating and released from rest, it remains at the surface. But if it is pushed deeper, it rises back up due to the buoyant force.
Q44. As an object is pushed deeper into water, the buoyant force
As an object is pushed deeper into water, the buoyant force increases until the object is fully immersed. This is because the buoyant force depends on the volume of fluid displaced. As more of the object is submerged, it displaces more water, so the buoyant force increases. Once the object is fully immersed, the buoyant force becomes constant regardless of depth (assuming constant fluid density). So the buoyant force increases with depth until full immersion.
Q45. Pressure increases when
Pressure P = F/A. For a constant force, if the area decreases, the pressure increases. This is why sharp objects (like knives and needles) have small areas to create high pressure. If the area increases, pressure decreases. Force and weight decreasing would decrease pressure, not increase it. So pressure increases when area decreases.
Q46. One pascal is equal to
One pascal (Pa) is defined as one newton per square metre (1 N/m²). This is the SI unit of pressure. It means that when a force of 1 newton is distributed over an area of 1 square metre, the pressure is 1 pascal. N/m is not a standard unit, N is the unit of force, and kg/m² is not a standard pressure unit.
Q47. The upward force on an immersed object is exerted by
The upward force on an immersed object (buoyant force) is exerted by the fluid (liquid or gas) in which the object is immersed. The fluid exerts pressure on all surfaces of the object. The pressure is greater at the bottom of the object than at the top, resulting in a net upward force. Earth exerts the downward force (gravity), and the surface supports objects, but the upward force comes from the fluid.
Q48. Ships made of iron float because of
Ships made of iron float because of buoyancy. Even though iron is denser than water, the ship’s shape allows it to displace a large volume of water. The weight of this displaced water is greater than the weight of the ship. This creates a large buoyant force that supports the ship’s weight. So the ship floats. If the same iron were in a solid block, it would sink because it would displace less water.
Q49. Pressure exerted by fluids depends on
Pressure exerted by fluids depends on the density of the fluid and the depth. The formula for fluid pressure is P = ρgh, where ρ is density, g is acceleration due to gravity, and h is depth. This shows that fluid pressure increases with greater depth and with higher fluid density. Area, shape, and colour do not affect fluid pressure.
Q50. Knives have sharp edges to
Knives have sharp edges to increase the pressure they exert. A sharp edge has a very small area. When the same force is applied through a small area, the pressure is very high according to P = F/A. This high pressure allows the knife to cut through materials easily. If the edge were blunt, the area would be larger, pressure would be lower, and cutting would be difficult.