When a body immersed fully or partially in a fluid it experiences an upward force that is equal to the weight of the fluid displaced by it.

Archimedes' principle:

Archimedes' principle is a fundamental principle in physics that explains the buoyant force experienced by an object immersed in a fluid. It was discovered by the ancient Greek mathematician and scientist, Archimedes of Syracuse, in the 3rd century BC.

Key Points:
- Archimedes' principle states that when an object is immersed in a fluid, it experiences an upward buoyant force equal to the weight of the fluid displaced by the object.
- The buoyant force acts in the opposite direction to the force of gravity and is responsible for the apparent weight loss of an object when submerged in a fluid.
- The principle is based on the concept that the pressure exerted by a fluid increases with depth. Therefore, the pressure on the bottom of the object is greater than the pressure on the top, resulting in a net upward force.
- The magnitude of the buoyant force can be determined using the formula: Fb = ρ × V × g, where Fb is the buoyant force, ρ is the density of the fluid, V is the volume of the fluid displaced, and g is the acceleration due to gravity.
- According to Archimedes' principle, an object immersed in a fluid will float if its weight is less than or equal to the buoyant force acting on it. Conversely, if the weight of the object is greater than the buoyant force, it will sink.
- The principle is applicable to both liquids and gases. However, in the case of gases, the buoyant force is often negligible due to their low density compared to solids or liquids.

Applications of Archimedes' principle:
- The principle explains why objects made of less dense materials, such as wood or plastic, float in water while denser materials, like metal, sink.
- It is the basis for designing and constructing ships, submarines, and other floating vessels, as it helps determine their stability and buoyancy.
- The principle is used in determining the purity of gold and other precious metals by measuring their buoyant force in a fluid.
- It is also utilized in various industries, such as oil and gas, to measure the density of fluids and determine the level in tanks or containers.

Overall, Archimedes' principle is a fundamental concept that helps us understand the behavior of objects submerged in fluids and has numerous practical applications in various fields.