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.

Multiple-Choice Questions

Answers

• Crash Course - Fluids at Rest (5:55)
• Michel van Biezen - Buoyancy Force
• Michel van Biezen - Archimedes Principle: Density of an Object
• Matt Anderson - Will It Float? Archimedes Principle
• Matt Anderson - How Much of an Iceberg is Under Water?

• Organic Chemistry Tutor - Archimedes Principle, Buoyant Force
• Organic Chemistry Tutor - How to Calculate the Fractional Volume Submerged

• Walter Lewin - Hydrostatics, Archimedes' Principle, Bernoulli's Equation
• Hyperphysics - Fluids

• oPhysics - Buoyancy simulation
• BU - Buoyancy simulation
• BU - Apparent weight and buoyancy simulation

Other Resources

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.