Why does a boat float in water but a boat anchor sinks? What actually causes something to float?
The answer is the buoyant force. This is an upwards force that acts on any object submerged in a fluid. But there's nothing magical about it - the buoyant force is just the net force caused by the fluid pressure, and since pressure increases with depth the net force is upwards.
While taking a bath, an ancient Greek physicist named Archimedes discovered that the upward buoyant force on a submerged object is equal to the weight of the fluid that the object displaces (known as Archimedes' principle).
In this lesson we'll learn about the buoyant force, how it works and how to calculate it.
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Free-Response Questions
Fluids (previously in AP Physics 2)
Note: These are questions from AP Physics 2 exams before 2025. For some questions only parts of the question are relevant to the Fluids unit in AP Physics 1 as noted below.
Why does a boat float in water but a boat anchor sinks? What actually causes something to float?
The answer is the buoyant force. This is an upwards force that acts on any object submerged in a fluid. But there's nothing magical about it - the buoyant force is just the net force caused by the fluid pressure, and since pressure increases with depth the net force is upwards.
While taking a bath, an ancient Greek physicist named Archimedes discovered that the upward buoyant force on a submerged object is equal to the weight of the fluid that the object displaces (known as Archimedes' principle).
In this lesson we'll learn about the buoyant force, how it works and how to calculate it.
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