Glossary
Acceleration due to gravity (g)
The constant acceleration experienced by objects falling freely near the Earth's surface, approximately 9.8 m/s² or 10 m/s².
Example:
When calculating the weight of an object, you multiply its mass by the acceleration due to gravity (g).
Apparent Weight (Wa)
The perceived weight of an object when it is submerged in a fluid, which is less than its true weight due to the buoyant force.
Example:
Lifting a heavy rock underwater feels easier because its Apparent Weight (Wa) is reduced by the water's upward push.
Archimedes' Principle
States that the buoyant force on an object submerged in a fluid is equal to the weight of the fluid displaced by the object.
Example:
A submarine adjusts its ballast tanks to displace more or less water, demonstrating Archimedes' Principle to control its depth.
Buoyancy
The upward force exerted by a fluid that opposes the weight of an immersed object.
Example:
When you push a beach ball underwater, the strong upward push you feel is buoyancy at work.
Buoyant Force (Fb)
The specific upward force exerted by a fluid on an object, equal to the weight of the fluid displaced by the object.
Example:
A ship stays afloat because the Buoyant Force (Fb) acting on its hull is equal to the ship's total weight.
Density (ρ)
A measure of mass per unit volume of a substance, indicating how much matter is packed into a given space.
Example:
Ice floats on water because its density is less than that of liquid water.
Equilibrium (Neutrally Buoyant)
The state where an object remains suspended at a constant depth within a fluid, neither rising nor sinking, because the buoyant force exactly equals its weight.
Example:
A fish can achieve Equilibrium by adjusting its swim bladder, allowing it to remain effortlessly at a specific depth without expending energy.
Floating
The condition where an object remains suspended on or within a fluid because the buoyant force acting on it is equal to or greater than its weight.
Example:
A log floating on a lake demonstrates that the water's upward push perfectly balances the log's downward weight.
Fluid
A substance that continuously deforms (flows) under an applied shear stress, including liquids and gases.
Example:
Both air and water are considered fluids because they can flow and take the shape of their container.
Net Force (Fnet)
The overall force acting on an object, which determines its acceleration according to Newton's second law.
Example:
If the upward buoyant force on a balloon is greater than its weight, there's a positive Net Force (Fnet) upwards, causing it to rise.
Pressure
The force exerted per unit area, which in fluids increases with depth and acts in all directions.
Example:
Deep-sea submersibles are built to withstand immense external pressure from the surrounding water.
Sinking
The condition where an object moves downwards through a fluid because its weight is greater than the buoyant force acting on it.
Example:
A rock dropped into a pond will sink because its density is much higher than water, resulting in a buoyant force less than its weight.
True Weight (Fg)
The actual gravitational force acting on an object, calculated as its mass multiplied by the acceleration due to gravity.
Example:
On a scale in air, your measurement reflects your True Weight (Fg), which is constant regardless of being in a fluid.
Volume of the object (V_object or V_displaced)
The amount of space an object occupies, which, when submerged, is equal to the volume of fluid it displaces.
Example:
To calculate the buoyant force on a fully submerged cube, you need its Volume of the object to determine how much water it pushes aside.