Buoyancy Practice Questions
19 free Buoyancy practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
What is buoyancy?
- A The upward force exerted by a fluid on an object immersed in it
- B The downward force exerted by Earth on an object
- C The resistive force that opposes relative sliding motion between two solid surfaces in contact
- D The force produced only by magnets
Correct answer: The upward force exerted by a fluid on an object immersed in it
Buoyancy is the upward force exerted by a fluid on an object placed in it. This force acts opposite to the object's weight.
The upward force acting on an object in a liquid is called:
- A Frictional force
- B Buoyant force
- C Magnetic force
- D Elastic force
Correct answer: Buoyant force
The buoyant force is the upward force exerted by a liquid or gas on an immersed object. It is responsible for making objects feel lighter in water.
An object will float in a liquid if:
- A Its density is less than the density of the liquid
- B Its density is greater than the density of the liquid
- C It has no volume
- D It is always made of metal
Correct answer: Its density is less than the density of the liquid
An object floats when its average density is less than that of the liquid. In this case, the buoyant force can balance its weight before it is fully submerged.
An object will sink in a liquid if:
- A Its density exceeds that of the liquid
- B Its density is less than the density of the liquid
- C It is hollow in all cases
- D It displaces no liquid at all
Correct answer: Its density exceeds that of the liquid
An object sinks if its density is greater than the density of the liquid. Its weight is then greater than the maximum buoyant force the liquid can provide.
Why does a ship made of steel float on water?
- A Its shape lowers its average density below water
- B Steel is always much less dense than water itself
- C Water has no weight at all
- D The ship does not displace any water
Correct answer: Its shape lowers its average density below water
A steel ship is hollow and contains air, which lowers its average density. It displaces enough water to produce a buoyant force equal to its weight.
Why does a stone usually sink in water?
- A It is denser than water
- B It has no mass
- C It repels water magnetically
- D It becomes weightless in water
Correct answer: It is denser than water
A stone usually has a density greater than water. Therefore, its weight exceeds the buoyant force acting on it, so it sinks.
Why does an object feel lighter when immersed in water?
- A An upward buoyant force acts on it
- B Its mass becomes zero in water
- C Gravity stops acting on it entirely
- D Its volume disappears completely
Correct answer: An upward buoyant force acts on it
Water pushes upward on the object with a buoyant force. This upward force reduces the object's apparent weight.
The apparent loss of weight of an object in a liquid is equal to:
- A The weight of displaced liquid
- B The mass of the object in air
- C The temperature of the liquid
- D The height of the entire container
Correct answer: The weight of displaced liquid
The apparent loss of weight is due to the buoyant force. By Archimedes' principle, this force equals the weight of the liquid displaced.
Which factor directly affects the buoyant force on a fully submerged object?
- A Density of the fluid
- B Color of the object
- C Shape of the container only
- D Brightness of light
Correct answer: Density of the fluid
Buoyant force depends on the weight of the fluid displaced. For a fully submerged object of fixed volume, denser fluids exert greater buoyant force.
Why is it easier to float in seawater than in freshwater?
- A Freshwater has no buoyant force at all
- B Seawater has no gravity
- C Freshwater is always hotter
- D Seawater is denser than freshwater
Correct answer: Seawater is denser than freshwater
Seawater contains dissolved salts, which make it denser than freshwater. A denser liquid provides a greater buoyant force for the same displaced volume.
A hydrometer is used to measure:
- A Electric current strength
- B Air pressure levels only
- C Speed of sound waves
- D Density relative to water
Correct answer: Density relative to water
A hydrometer floats at different levels depending on the density of the liquid. It is used to measure the relative density or specific gravity of liquids.
Why does a hydrometer float higher in a denser liquid?
- A It becomes much heavier in a very dense liquid
- B The liquid completely removes gravity
- C It absorbs the liquid and then expands
- D It displaces less liquid to balance weight
Correct answer: It displaces less liquid to balance weight
In a denser liquid, a smaller volume of liquid has enough weight to balance the hydrometer's weight. Therefore, the hydrometer does not sink as deeply and floats higher.
Which of the following best explains why ice floats on water?
- A Ice has no weight
- B Water does not exert buoyant force
- C Ice is heavier than liquid water
- D Ice is less dense than water
Correct answer: Ice is less dense than water
Ice has a lower density than liquid water due to its open crystal structure. Therefore, it floats with part of its volume above the water surface.
When an object floats, the buoyant force is:
- A Always zero
- B Greater than gravity forever
- C Equal to the mass of the object only
- D Equal to the weight of the object
Correct answer: Equal to the weight of the object
A floating object is in equilibrium, so the upward buoyant force balances its downward weight. This is why it stays at the surface without sinking further.
When an object is completely submerged and still sinking, its weight is:
- A Equal to zero
- B Less than the buoyant force
- C Unrelated to any force
- D Greater than buoyant force
Correct answer: Greater than buoyant force
If a submerged object continues to sink, the downward force of its weight is greater than the upward buoyant force. The net force acts downward.
Which fluid can exert buoyant force?
- A Solids and metals
- B Liquids and solids
- C Liquids and gases
- D Gases and vacuum
Correct answer: Liquids and gases
A fluid is a substance that can flow, including liquids and gases. Both liquids and gases exert buoyant force on objects placed in them.
Why do hot air balloons rise?
- A Hot air has no mass at all
- B Gravity acts upward on the whole balloon
- C Hot air is less dense than cool air
- D The balloon does not displace air
Correct answer: Hot air is less dense than cool air
Heating air makes it expand and become less dense than the cooler air outside. The surrounding air provides a buoyant force that can lift the balloon.
Which principle explains why a submarine can float, sink, or remain suspended in water?
- A Reflection of light
- B Magnetic attraction effects only
- C Adjusting average density
- D Evaporation of water
Correct answer: Adjusting average density
A submarine changes its average density by taking in or expelling water from ballast tanks. This changes the balance between its weight and buoyant force.
If two objects have the same volume and are fully submerged in the same liquid, which one experiences greater buoyant force?
- A The heavier object always experiences greater buoyant force
- B The lighter object always experiences greater buoyant force
- C Both objects experience exactly the same buoyant force
- D The darker object experiences greater buoyant force
Correct answer: Both objects experience exactly the same buoyant force
For fully submerged objects in the same liquid, buoyant force depends on the volume of liquid displaced. If both objects have the same volume, they displace the same amount of liquid and experience the same buoyant force.