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Archimedes Principle, Buoyancy, Flotation, Pascal's Principle

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A series of free Online High School Physics Video Lessons.

In these lessons, we will learn

  • Archimedes' Principle
  • Buoyancy
  • Flotation
  • Pascal's Principle

Archimedes' Principle

Archimedes' principle states that the buoyant force on a fluid is equal to the weight of the displaced fluid.
To calculate the buoyant force, we use the equation
buoyant force = density of fluid × volume of displaced fluid × acceleration due to gravity.
In a completely submerged object, the volume of displaced fluid equals the volume of the object. If the object is floating, the volume of of the displaced fluid is less than the volume of the object but the buoyant force = the weight of the object.

How to find buoyant force for floating and submerged objects? How to demonstrate and explain Archimedes' principle?


Buoyant force is the force that a fluid exerts on a object that is immersed within it. It is called buoyant force because this force is a lifting force, often making the object buoyant. Buoyant force can be calculated using Archimedes' Principle.

Word Problems to help you understand buoyant force and Archimedes' Principle
1. Find the buoyant force on 4 × 10-4 of iron immersed in water.

2. Find the buoyant force on 20 kg of iron immersed in water.

3. Find the buoyant force of 75N of copper immersed in water.

4. A crown weighs 35N in air and 32N in water. Determine its density.

What is the relationship between buoyancy and density?
Explains the relationship between buoyancy and density using hot air balloons, fish and cruise ships as examples of objects using buoyant force.
Includes instructions for calculating the density of a rectangular prism and a liquid.
Includes a brief explanation of Archimedes' Principle and the role gravity plays in buoyant force.

Flotation or Floatation

In floatation, the buoyant force equals the weight of the floating object and the volume of the object is always greater than the volume of water displaced. Floatation can be calculated using Archimedes' Principle.

How the mass of a floating object is related to its buoyant force
1. What fraction of the volume of an iceberg is visible above oceanwater?

2. A raft is 25m × 10m × 20cm and weighs 20N. An 800N person climbs on the raft. How many centimeters of the raft are visible above the surface? What is the maximum weight the raft can support?

Explains and demonstrates how and why things float

Pascal's Principle

According to Pascal's Principle, in a uniform fluid, pressure depends only on height. There can be no pressure gradient except for that caused by liquid pressure. This is seen in hydraulic jacks which are used to lift heavy objects.
In a uniform fluid, pressure depends only on height.


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You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.

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