Archimedes Principle Quiz: Test Your Fluid Physics Knowledge

9th Grade

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| Attempts: 14 | Questions: 20 | Updated: Mar 13, 2026

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1. Archimedes’ principle states that the buoyant force equals:

The object’s mass

The weight of the fluid displaced

The object’s volume

The fluid’s temperature

Concept: Archimedes’ principle. Buoyant force is equal to the weight of displaced fluid. This links buoyancy directly to displaced volume and fluid density.

Explanation

Concept: Archimedes’ principle. Buoyant force is equal to the weight of displaced fluid. This links buoyancy directly to displaced volume and fluid density.

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About This Quiz

Archimedes Principle Quiz: Test Your Fluid Physics Knowledge - Quiz

This assessment focuses on Archimedes' Principle and its applications in fluid physics. It evaluates your understanding of buoyancy, density, and the behavior of objects submerged in fluids. Engaging with this content is essential for students and enthusiasts looking to deepen their grasp of fluid mechanics and its real-world implications.

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2. A larger displaced volume generally means a larger buoyant force (in the same fluid).

True

False

Concept: Displacement dependence. Displacing more fluid increases the weight of displaced fluid. That increases buoyant force.

Explanation

Concept: Displacement dependence. Displacing more fluid increases the weight of displaced fluid. That increases buoyant force.

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3. The buoyant force formula can be written as:

F_b = m/v

F_b = ρ_fluid · g · v_displaced

F_b = ρ_object · g · v_object always

F_b = g/ρ

Concept: Buoyant force formula. Buoyant force depends on fluid density, gravity, and displaced volume. It does not directly depend on object density except through how much volume is submerged.

Explanation

Concept: Buoyant force formula. Buoyant force depends on fluid density, gravity, and displaced volume. It does not directly depend on object density except through how much volume is submerged.

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4. In f_b = ρgv, ρ is the ______ of the fluid.

Concept: Meaning of ρ. ρ measures how much mass is in a given volume. A denser fluid provides more buoyant force for the same displaced volume.

Explanation

Concept: Meaning of ρ. ρ measures how much mass is in a given volume. A denser fluid provides more buoyant force for the same displaced volume.

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5. If you submerge the same object in fresh water and salt water (salt water is denser), the buoyant force is:

Smaller in salt water

Larger in salt water

The same in both

Zero in salt water

Concept: Fluid density effect. Higher fluid density increases ρ in ρgv. So the buoyant force increases in salt water for the same displaced volume.

Explanation

Concept: Fluid density effect. Higher fluid density increases ρ in ρgv. So the buoyant force increases in salt water for the same displaced volume.

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6. The apparent weight of an object underwater equals its true weight minus buoyant force.

True

False

Concept: Apparent weight relation. A scale measures the net force the object exerts on it. Buoyancy reduces that net force, making the object 'feel lighter.'

Explanation

Concept: Apparent weight relation. A scale measures the net force the object exerts on it. Buoyancy reduces that net force, making the object 'feel lighter.'

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7. An object weighs 20 N in air and has a buoyant force of 6 N in water. Its apparent weight underwater is:

26 N

14 N

6 N

3 N

Concept: Subtracting buoyant force. Apparent weight = 20 N − 6 N = 14 N. The buoyant force 'supports' part of the weight.

Explanation

Concept: Subtracting buoyant force. Apparent weight = 20 N − 6 N = 14 N. The buoyant force 'supports' part of the weight.

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8. If an object is fully submerged, the buoyant force depends on the object’s shape only through the volume it displaces.

True

False

Concept: Volume matters most. For full submersion, displaced volume equals object volume. Shape matters only in how it affects volume, not directly.

Explanation

Concept: Volume matters most. For full submersion, displaced volume equals object volume. Shape matters only in how it affects volume, not directly.

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9. A floating object displaces water whose weight is:

Always greater than the object’s weight

Always less than the object’s weight

Equal to the object’s weight

Unrelated to the object

Concept: Floating equilibrium. When floating, buoyant force equals weight. By Archimedes, that equals the weight of displaced fluid.

Explanation

Concept: Floating equilibrium. When floating, buoyant force equals weight. By Archimedes, that equals the weight of displaced fluid.

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10. If an object floats, its average density is ______ than the fluid’s density.

Concept: Density condition for floating. Lower average density means less mass per volume than the fluid. Then the object can balance its weight with partial submersion.

Explanation

Concept: Density condition for floating. Lower average density means less mass per volume than the fluid. Then the object can balance its weight with partial submersion.

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11. A wood block floats with 60% of its volume submerged in water. Its density compared with water is closest to:

1.6 times water

1.0 times water

0.6 times water

0.06 times water

Concept: Fraction submerged. For floating, fraction submerged ≈ ρ_object / ρ_fluid. If 60% is submerged, density is about 0.6 of water.

Explanation

Concept: Fraction submerged. For floating, fraction submerged ≈ ρ_object / ρ_fluid. If 60% is submerged, density is about 0.6 of water.

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12. For a floating object, adding mass causes it to displace more water.

True

False

Concept: More weight → more displacement. The object must increase displaced volume so buoyant force grows. That is why it sits lower.

Explanation

Concept: More weight → more displacement. The object must increase displaced volume so buoyant force grows. That is why it sits lower.

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13. Which change increases buoyant force on a fully submerged object most directly?

Decrease g

Decrease ρ_fluid

Increase displaced volume

Make the object darker

Concept: f_b = ρgv. Increasing v increases buoyant force linearly (if ρ and g stay the same). Colour is irrelevant.

Explanation

Concept: f_b = ρgv. Increasing v increases buoyant force linearly (if ρ and g stay the same). Colour is irrelevant.

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14. An object can sink even if it experiences a buoyant force.

True

False

Concept: Buoyancy always exists. Buoyant force exists for any submerged object, but it may be smaller than weight. If weight is greater, the object sinks.

Explanation

Concept: Buoyancy always exists. Buoyant force exists for any submerged object, but it may be smaller than weight. If weight is greater, the object sinks.

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15. Which statements are correct?

Buoyant force depends on fluid density

Buoyant force depends on displaced volume

Buoyant force depends on object’s mass directly

A floating object displaces its own weight of fluid

Concept: Key relationships. Mass affects floating indirectly through how much volume must be submerged. The direct dependence is on ρ, g, and v.

Explanation

Concept: Key relationships. Mass affects floating indirectly through how much volume must be submerged. The direct dependence is on ρ, g, and v.

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16. A sealed container floats higher in water than in oil because:

Water is always warmer

Water’s density is higher, so less volume needs to be submerged

Oil has no buoyancy

The container changes mass

Concept: Higher ρ means more buoyant force per volume. In denser water, a smaller displaced volume can balance the same weight. So the container sits higher.

Explanation

Concept: Higher ρ means more buoyant force per volume. In denser water, a smaller displaced volume can balance the same weight. So the container sits higher.

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17. Neutral buoyancy occurs when buoyant force equals weight and net force is zero.

True

False

Concept: Neutral buoyancy. With net force zero, the object neither rises nor sinks. This often corresponds to equal average density with the fluid.

Explanation

Concept: Neutral buoyancy. With net force zero, the object neither rises nor sinks. This often corresponds to equal average density with the fluid.

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18. If an object’s density is exactly equal to the fluid density, it will most likely:

Float with half its volume submerged

Sink to the bottom

Remain suspended if placed fully in the fluid (neutral buoyancy)

Rise rapidly to the top

Concept: Equal densities. Equal density means weight equals buoyant force for full submersion. It will not accelerate up or down if fully submerged and not touching boundaries.

Explanation

Concept: Equal densities. Equal density means weight equals buoyant force for full submersion. It will not accelerate up or down if fully submerged and not touching boundaries.

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19. The buoyant force changes if the fluid density changes (for example, with temperature).

True

False

Concept: Density variation. Heating often lowers fluid density, reducing buoyancy for the same volume displaced. This can change floating depth.

Explanation

Concept: Density variation. Heating often lowers fluid density, reducing buoyancy for the same volume displaced. This can change floating depth.

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20. Grade 9 wrap-up: A good way to check a buoyancy calculation is to ask whether the result matches:

The object’s colour

The weight of the displaced fluid for the same volume

The object’s temperature only

The container’s shape only

Concept: Archimedes as a consistency check. Buoyancy should match displaced fluid weight. If your result doesn’t scale with ρ and v correctly, something is off.

Explanation

Concept: Archimedes as a consistency check. Buoyancy should match displaced fluid weight. If your result doesn’t scale with ρ and v correctly, something is off.

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