Have you ever wondered why a tiny iron nail sinks instantly to the bottom of a bucket, but a massive cruise ship made of millions of tons of steel floats perfectly on the ocean? Or why it is so easy to lift a heavy friend inside a swimming pool? The scientific answer to all of this is Buoyancy.
The mathematical calculation of this upward force was discovered by the ancient Greek genius Archimedes. Archimedes' Principle states that the upward buoyant force is exactly equal to the weight of the water displaced (pushed out of the way) by the object.
Whenever you submerge an object in a fluid (like water or air), the fluid pushes back against the object.
Definition: The upward force exerted by a fluid on an object completely or partially immersed in it is called Buoyancy (or the Buoyant Force / Upthrust).
Because of this upward push, objects inside water feel much lighter than their actual weight on land.
It is caused by pressure differences. When a block is put in water, the water pushes against it from all sides. However, water pressure drastically increases with depth. Therefore, the water pushing up against the bottom of the block is much stronger than the water pushing down on the top of the block. This unequal pressure creates a net upward push—the Buoyant Force.
Whether an object floats or sinks depends entirely on a tug-of-war between Gravity (pulling down) and Buoyancy (pushing up).
No! Buoyancy applies to all fluids, which includes **Gases**. The only reason a Hot Air Balloon or a Helium balloon floats up into the sky is because of the buoyant force exerted by the surrounding air!
SI Unit of Length
The SI unit of length is the metre (m). Defined as the distance light travels in vacuum in 1/299,792,458 seconds. Learn prefixes: km, cm, mm, nm, Å.
SI Unit of Pressure
The SI unit of pressure is the Pascal (Pa). 1 Pa = 1 N/m². Atmospheric pressure = 101,325 Pa. Learn formula, dimensional formula, and unit conversions.
SI Unit of Resistance, Resistivity, and Capacitance
Learn the SI units of electrical resistance (Ohm), resistivity (Ohm-meter), and capacitance (Farad). Understand their definitions and formulas.
SI Unit of Resistivity — Ohm-Metre (Ω·m)
The SI unit of resistivity is ohm-metre (Ω·m). Derived from ρ = RA/L. Definition, formula, dimension, and resistivity values of common materials explained.
What is the SI Unit of Time?
Learn the SI unit of time. Understand why the Second (s) is the universal standard for measuring time and how it is scientifically defined.
Turn this guide into revision flashcards, a practice exam, or an AI-generated podcast — free, no signup required.