Glossary
Archimedes' Principle
States that the buoyant force on a submerged object is equal to the weight of the fluid displaced by the object.
Example:
When you place an ice cube in a glass of water, Archimedes' Principle explains why it floats with a portion submerged, as the buoyant force equals the weight of the water it pushes aside.
Bernoulli's Equation
An equation derived from the conservation of energy for ideal fluids, relating pressure, fluid velocity, and height at two points along a streamline.
Example:
Engineers use Bernoulli's Equation to design efficient pipelines, predicting how pressure changes as water flows through pipes of varying diameters and elevations.
Bernoulli's Principle
States that for an ideal fluid in steady flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.
Example:
The lift on an airplane wing is explained by Bernoulli's Principle, where faster-moving air above the wing creates lower pressure, pulling the wing upward.
Buoyancy Force (F_b)
The upward force exerted by a fluid on an object submerged in it, opposing the object's weight.
Example:
A boat floats on water because the buoyancy force exerted by the displaced water is equal to the boat's weight.
Closed System
A fluid system that does not exchange matter or energy with its surroundings.
Example:
A perfectly insulated, sealed thermos containing hot coffee represents a closed system where neither mass nor heat can enter or leave.
Conservation of Energy
A fundamental principle stating that in a closed system, the total energy remains constant; energy can change forms but is never created or destroyed.
Example:
As water flows down a waterfall, its potential energy converts to kinetic energy, but the total conservation of energy of the water-Earth system remains constant.
Conservation of Mass
A fundamental principle stating that in a closed system, the total mass remains constant; mass cannot be created or destroyed.
Example:
When a balloon is inflated and sealed, the total mass of the air inside the balloon remains constant, demonstrating the conservation of mass.
Continuity Equation
An equation derived from the conservation of mass for ideal fluids, stating that the product of the cross-sectional area and the fluid velocity is constant along a streamline.
Example:
When you squeeze the nozzle of a garden hose, the water speeds up because the continuity equation dictates that a smaller area requires a higher velocity to maintain the same flow rate.
Density (ρ)
A measure of how much mass is contained in a given volume of a substance, defined as mass per unit volume.
Example:
A lead fishing sinker has a much higher density than a cork bobber of the same size, which is why the sinker sinks and the bobber floats.
Drag Force
A resistive force that opposes the motion of an object through a fluid, acting in the opposite direction of the object's velocity.
Example:
A swimmer feels a significant drag force from the water, which they must overcome to move forward.
Fluid Weight Force
The downward force exerted on a fluid due to gravity, calculated as the mass of the fluid multiplied by the acceleration due to gravity.
Example:
The fluid weight force of the water in a tall glass pushes down on the bottom of the glass.
Free-Body Diagram (FBD)
A visual representation used to analyze forces acting on an object, showing the object as a point or simple shape with arrows representing each force.
Example:
To determine if a hot air balloon will rise, one would draw a free-body diagram showing the upward buoyant force and the downward weight of the balloon and its contents.
Hydrostatic Pressure
The pressure exerted by a fluid at rest due to the force of gravity, acting equally in all directions at a given depth.
Example:
Divers experience increasing hydrostatic pressure as they descend deeper into the ocean, feeling the force of the water above them.
Intensive Property
A physical property of a system that does not depend on the system size or the amount of material in the system.
Example:
The intensive property of water's boiling point is 100°C, whether you have a cup or a swimming pool full of it.
Mass Flow Rate (Q)
The mass of a fluid passing through a given cross-sectional area per unit time, which remains constant in a closed system.
Example:
In a river, the mass flow rate of water is constant, meaning that if the river narrows, the water must flow faster to maintain the same amount of mass passing through per second.
Net Force
The vector sum of all individual forces acting on an object, which determines the object's acceleration according to Newton's second law.
Example:
If the upward buoyant force on a submerged object is greater than its downward weight, there is a positive net force upward, causing the object to accelerate upwards.
Open System
A fluid system that exchanges both matter and energy with its surroundings.
Example:
A boiling pot of water on a stove is an open system because steam (matter) escapes and heat (energy) is transferred to the air.
Pascal's Principle
States that a pressure change at any point in a confined incompressible fluid is transmitted undiminished to every portion of the fluid and to the walls of its container.
Example:
A hydraulic lift uses Pascal's Principle to multiply force; a small force applied to a small piston creates a much larger force on a larger piston.
Pressure (P)
The amount of force applied perpendicular to the surface of an object per unit area over which that force is distributed.
Example:
A person wearing snowshoes distributes their weight over a larger area, reducing the pressure on the snow and preventing them from sinking.