Density and Pressure

m over v
mass per volume
specific gravity
density fluid


Density is a measure of mass per volume of a material and is an intensive property that does not depend on the quantity of material. The equation for density is mass (M) over volume (V). Specific gravity is another term for the density of a liquid, which compares the density of an object or substance to the density of water.

Buoyant force is the upward push that a fluid exerts on any object placed in that fluid. Archimedes' principle helps predict the buoyant force on an object, stating that the buoyant force is equal to the weight of the fluid displaced. Pressure results from a force being spread over some area and can be measured in absolute or gauge pressure. When it comes to pressure, gauge pressure is the amount of pressure over normal atmospheric pressure. To get the true (absolute) pressure from gauge pressure, add the atmospheric pressure above the liquid - under normal conditions, this is one atmosphere (1 atm).

Lesson Outline

<ul> <li>Density</li> <ul> <li>Measure of mass per volume of a material</li> <li>Example: Density of water is 1000 kg/m³</li> <li>Equation: Density = mass/volume (M/V)</li> <li>Specific Gravity - comparison of density to that of water</li> </ul> <li>Buoyant Force</li> <ul> <li>Upward push that a fluid exerts on objects</li> <li>Archimedes' principle: buoyant force is equal to the weight of displaced fluid</li> <li>Equation: Buoyant force = density × volume × acceleration of gravity</li> </ul> <li>Pressure</li> <ul> <li>Force spread out over an area</li> <li>Equation: Pressure = force/area (F/A)</li> <li>Unit: Pascal (Newton per meter squared)</li> <li>Depth in a liquid affects pressure</li> <li>Gauge Pressure vs. True (Absolute) Pressure</li> </ul> <li>Blood Pressure</li> <ul> <li>Systolic Pressure: Pressure during a heartbeat</li> <li>Diastolic Pressure: Pressure between heartbeats</li> </ul> </ul>

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What are density, pressure, and buoyancy?

Density is the mass per unit volume of a substance, and pressure is the force exerted on a surface area within a fluid. Buoyant force is the upward force exerted by a fluid against an object submerged in it. When an object is submerged in a fluid, it experiences a buoyant force that is determined by the density of the fluid and the volume of the displaced fluid.

What is Archimedes' principle, and how does it apply to understanding buoyant force in fluids?

Archimedes' principle states that the upward buoyant force exerted on a submerged object is equal to the weight of the fluid that the object displaces. In other words, an object submerged in a fluid experiences an upward force equal to the weight of the fluid it has displaced. This principle helps in calculating the buoyant force experienced by the object in different fluids and understanding the factors that affect the object's buoyancy or tendency to float or sink.

How is specific gravity used in comparing the densities of various substances, and how does it relate to buoyancy?

Specific gravity is the ratio of a substance's density to the density of a reference substance (typically water). It is a dimensionless value that helps in comparing the densities of different substances relative to the reference substance. A substance with a specific gravity greater than 1 is denser than the reference substance, while a specific gravity less than 1 indicates a less dense substance. If an object's specific gravity is less than the fluid's specific gravity, the object will float; if it is greater, the object will sink.

How are gauge pressure and absolute pressure different when measuring fluid pressures, such as blood pressure or underwater pressure?

Gauge pressure is the pressure relative to atmospheric pressure, which is the pressure that the fluid exerts without considering the influence of the Earth's atmosphere. Absolute pressure, on the other hand, includes atmospheric pressure and is the actual total pressure exerted on a surface. For example, blood pressure measurements are gauge pressures because they, too, are relative to atmospheric pressure.