Archimedes Principle and Buoyancy: Detail Explanation, applications and Examples

Archimedes Principle and Buoyancy

Archimedes Principle basically refers to the upward force exerted by water or any type of fluid when an object is immersed in it. For better understanding, we should first understand the basic terminology like Thrust, Upthrust, Flotation, Buoyancy, Pressure, etc. In this article, we will provide complete information regarding the Archimedes Principle along with its basics and applications.

Before understanding the Archimedes Principle we will first understand the core concept and terminology used in these principles.

Thrust and Up Thrust

Thrust is nothing but a force applied perpendicular in direction on the surface. Basically, Thrust is a type of force which have direction, as the force having direction comes under vector quantity. So, we can measure the Thrust in Newton. When the force is applied in the body in an upward direction those forces are called Up Thrust.


Pressure refers to the amount of force applied to an object at a particular unit area. So in simple terms, the force acting on that particular area is calculated using Pressure. The unit at which Pressure is measured is Newton per Meter square or Pascal. The formula of the Pressure is Thrust/ Area.

Application of Pressure

Here we explain the Pressure’s Application with real-life examples

  • Army Tanks: Everyone knows that Army Tanks have tonnes of weight therefore they may exert a large force on the ground. But on applying the concepts of pressure their wheels are designed in such a way that they are wide from the bottom. So because of provides a high surface area at the bottom, the tank does not exert that much force according to its weight.
  • School Bags: The strips of the School Bags are designed by applying this concept so that the weight of the school bags does not hurt the student’s shoulder. So by providing a wide surface area of a strip on the bag, it exerts less pressure.
  • Needle’s Tip: The tips of the needle are formed sharp so as to exert high pressure on the small surface area. so using this application will help the needle pierce the clothes easily.


Buoyancy: Buoyancy is the phenomenon by which water or any fluid exerts upward force (Upthrust) when an object is immersed in it. The upward force applied to the object is called buoyant force. For better understanding we can say that Buoyancy is nothing but an Upthrust exerted by the liquid. For example, when a cork is immersed in the water 2/3 of it parts help in float. when we apply force to sink at the bottom, then with the phenomenon of buoyancy it will automatically come to the surface of the water.

Factors Affecting Buoyancy

The upward force basically depends on two concepts density of the fluid at which the body is submerged and the volume of the body submerged.

  • Surface Area: Increasing the surface area of the body that is immersed in the fluid the upward force is also increased. Explaining the concept with a real-life example if you immerse a small piece of wood you can easily sink it inside the water but if you immerse the large plank of wood and apply force to sink in the water then you have to apply more force greater than the upthrust exert by the water. Hence it proves that surfaces matter most in buoyancy.
  • Fluid Density: Different fluids have different densities so the fluid having greater density exerts greater Upthrust in comparison to a fluid having less density.

Cause of Buoyancy

The main cause of Buoyancy is because of the molecules present in the fluid. When the fluid is at rest the molecules of the liquid exert a perpendicular force when they come in contact with the body. For example when the fluid is in any container then at the surface of the container it exerts the perpendicular force. The pressure or the upward force you feel is because of the collision of the molecules that takes place with the surroundings when the object is immersed within the liquid.

The force of Buoyancy is the same in all directions but different at increasing the depth. The buoyant force is the same in all directions because of the same no of molecules present in that particular depth which led to equal force exerted by the molecules at that place. The buoyant force is different at depth because of the increase in the molecules in the depth which led to more collisions between the molecules at that place hence exerting more force.

Effects of Buoyancy on Different Weight

Here we understand the concept of Buoyancy of Different weight objects. For Which (W) stands for the downward force applied by the object immersed in the fluid and (U) stands for the upward force exerted by the water. In this floatation of the object depends upon the net force between U and W.

  • Case 1: When W is Greater than U which means when the downward force exerted by the object is greater than the upward force exerted by the liquid then the object is going to sink. As there is no balancing of the force situation takes place so the greater force suppresses the smaller force and hence goes in the direction of the greater force so the object is going to sink into the liquid.
  • Case 2: When U is Greater than W which means when the Upthrust or upward force exerted by the liquid is greater than the Downward force exerted by the object then the object is going to float in the liquid. As there is no balancing situation taking place so the greater force suppresses the smaller force and hence goes in the direction of the greater force so the object is going to float in the liquid.
  • Case 3: When U is equal to W which means the force exerted by the object is equal to the upward force exerted by the liquid hence object is in the equilibrium situation. In a balancing situation, both forces cancel out each other so there is no motion of the object taking place.

Archimedes Principle

Archimedes’s Principle basically works on the phenomenon of Buoyancy and observes that “The upward force experienced by the object when it is placed in the liquid is equal to the weight of the fluid displaced by the object.” It is like when the object is placed it displaces the weight of the fluid and exerts the upward force. so the fluid displaced and the upward force exerted are equal.

The formula of the upward buoyant force is Fb =  ρ x g x V.

Where ρ denotes the density of the liquid, g denotes the acceleration caused by gravity and V denotes the volume of the liquid.

Archimedes Principle Application

  • Submarine: With the help of Archimedes Principles the submarine is designed in such a way that it helps to make submarine at any position underwater. There is an important component used in Submarines is the Ballast Tank it allows the entering and exit of water so that we can place the submarine in the position of which we want.
  • Hydrometer: Hydrometer works on the principle of Archimedes, it is the instrument used to measure the relative density. It consists of lead shots which help it in floatation so the deeper the hydrometer sinks the less the density of fluids.
  • Geology: The principles help in understanding the sedimentation profile by measuring the denser particle float on the liquid top.

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