Flashcards: MCAT Physics and Math 4.2: Hydrostatics

Hydrostatics is the study of fluids at rest and the forces and pressures associated with standing fluids.

Fluids with volumes that cannot be reduced by any significant degree through application of pressure

For fluids that are incompressible, a change in pressure will be transmitted undiminished to every portion of the fluid and to the walls of the containing vessel.

Hydraulic systems function and perform tasks through using a fluid that is pressurized.

mechanical advantage

isobaric

larger

smaller

An upward force exerted by a fluid that opposes the weight of a partially or fully immersed object.

The upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces.

F_buoy = ρ_fluidV_{fluid displaced}g = ρ_fluidV_submergedg

fluid itself

... its average density is less than the average density of the fluid it is immersed in.

... its average density is greater than that of the fluid.

... the same magnitude of buoyant force.

... the force of the liquid trying to return to the space from which it was displaced, thus trying to push the object up and out of the water.

... the percent of the object’s volume that is submerged (when the fluid is pure water).

The tendency of liquid surfaces at rest to shrink into the minimum surface area possible

The attractive force that a molecule of liquid feels toward other molecules of the same liquid

Consider the intermolecular forces between the separate molecules of liquid water. For those molecules below the surface, there are attractive intermolecular forces coming from all sides; these forces balance out. However, on the surface, the molecules only have these strong attractive forces from the molecules below them, which pulls the surface of the liquid toward the center. This establishes tension in the plane of the surface of the water; when there is an indentation on the surface (say, caused by a water strider’s foot), then the cohesion can lead to a net upward force.

The attractive force that a molecule of the liquid feels toward the molecules of some other substance

The curve in the upper surface of a liquid close to the surface of the container or another object, produced by surface tension

A backwards (convex) meniscus (with the liquid level higher in the middle than at the edges) occurs when the cohesive forces are greater than the adhesive forces.

backward meniscus

A concave meniscus, or curved surface in which the liquid “crawls” up the side of the container a small amount, will form when the adhesive forces are greater than the cohesive forces.