Buoyancy and Archimedes' Principle

Upthrust in Fluids, Archimedes' Principle and Floatation

• Buoyancy, upthrust (F_B), definition, different cases, experimental determinations of relative density (R.D.) of a solid.
• Scope: Buoyancy, Archimedes' principle, properties of upthrust, and floating objects. Examples include application to ships, submarines, icebergs, balloons.
• Archimedes' principle: Relationship between the density of a floating body and the density of the fluid in which it is floating, and the fraction of the volume immersed.
• Principle of flotation: Density of the floating body is related to the density of the liquid in which it floats.
• Simple numerical problems on Archimedes' principle.
• Application to ships and submarines relating calculation and floatation.

Buoyancy and Upthrust

• When a body is partially or wholly immersed in a liquid, an upward force acts on it. This upward force is known as upthrust or buoyant force (F_B).
• The upward force exerted on a body by the fluid in which it is submerged, is called the upthrust or buoyant force.
• The property of a liquid to exert an upward force on a body immersed in it is called buoyancy.
• Experiments demonstrate buoyancy
  • Pushing an empty can into water: If you push a can into water, you feel an upward force opposing the push. The more you push the can underwater the bigger the upward force becomes until the can is fully submerged.
  • Pushing a cork into water: A cork placed on the surface of water floats, with some of its volume underwater. If the cork is submerged and released, it returns to the surface.
• Explanation:
  • When a can or cork is placed in water, two forces act on it: (i) its weight (W) pulling downwards and (ii) the upthrust (F_B) pushing upwards.
  • It floats when the two forces are equal in magnitude (W=F_B).
  • When the can or cork is pushed deeper the upward force increases until it becomes maximum (F'_B) when it is completely immersed.
  • When released, if F'_B is greater than W, it will rise to the surface. If F'_B is less than W, it continues downwards until W=FB
  • To keep the object immersed, an external force (F’_B-W) is required.

Test your knowledge on buoyancy, upthrust, and Archimedes' Principle with this quiz. Explore the relationship between density, flotation, and the applications of these principles in real-world scenarios like ships and submarines. Solve numerical problems to enhance your understanding of these concepts.