Physics Lab
Physics Lab
  Complete and Continue  

Buoyant Force

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.

Study guide with the variables, equations and examples of buoyant force, displaced fluid and Archimedes' principle
2

Buoyant Force
1

Answers

3

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.

  • 2023 Q3 - - Tank of water with pipe and two blocks, fluids, forces, buoyant force, flow, Bernoulli's equation, continuity equation
  • 2022 Q1 - - (Part a) Block in tank of water hanging from string, fluids, forces, FBDs, buoyant force
  • 2021 Q2 - - (Parts b and c) Balloon held underwater, fluids, density, pressure, forces, buoyant force
  • 2018 Q4 - - (Parts a and c) Boat carrying steel bars, fluids, forces, buoyant force, flow, continuity equation
  • 2017 Q1 - - Water flowing through pipe, fluids, flow, continuity equation, Bernoulli's equation, conservation of energy, forces, FBDs, buoyant force

Buoyancy (PhET)
Jared Schmidt, Diana Lopez

Lab 1 - The Cartesian Diver
empty 2L plastic bottle with cap, drinking glass, water, plastic straw, scissors, paper clips, eyedropper (optional)
Rhett Allain

Lab 2 - Floating Eggs
2 glasses, 2 eggs, salt
Math and Science

Lab 1 - Fluid Dynamics (Pages 123-124, Activity 3)
scale, object that sinks in water, object that floats in water, water and three other liquids with different densities, graduated cylinder, at least four objects with irregular shapes
Openstax - College Physics for AP Courses Lab Manual - Student Version

Lab 2 - Buoyant Force
force sensor with hook, support for force sensor, overflow can, brass cylinder, aluminum cylinder, scale, thread, beakers, glass stir rod, pen, dish soap, water, meterstick
Pasco

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.

Buoyant Force
Complete and Continue