Buoyancy is a/an
- A.upward pressure
- B.downward pressure
- C.downward force
- D.upward force
Correct answer
Explanation
The correct answer is D, upward force. Buoyancy, or upthrust, is the upward force a fluid exerts on any object immersed in it.
A fluid presses on an object from all sides, but the pressure grows with depth, so the push on the lower surface is greater than the push on the upper surface. The difference is a net upward force called buoyant force. Archimedes' principle states that this force equals the weight of the fluid displaced by the object. If the buoyant force is greater than or equal to the object's weight, the object floats; if it is less, the object sinks. This is why a heavy steel ship floats: its hollow shape displaces a large weight of water.
A is wrong because buoyancy is a force measured in newtons, not a pressure measured in pascals, even though it arises from a pressure difference. B is wrong because buoyancy acts upward and is not a pressure. C is wrong because the downward force on an object is its weight; buoyancy opposes it.
Exam tip: buoyant force = weight of fluid displaced (Archimedes); an object floats when this equals its own weight.
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