Chapter 4: Fluids Flashcards

Question

Again. What are the three equations from Pascal’s principle regarding pressure volume and work?

Answer 1

The question provided a radius and a force. We can use Pascal’s principle and proportion of force and area. We need to take the radius and calculate the area. Radius of a circle is pi r^2.

Answer 2

Archimedes principal deals with the buoyancy of objects when placed in a fluid. The principal states that a body wholly or partially immersed in a fluid will be buoyed upward by a force equal to the weight of the fluid that it displaces.

Answer 3

I figured out a super easy way to solve this problem using specific gravity ratio. If 50% of the wood is submerged, then that means its specific gravity is 0.5 compared to whatever fluid it is submerged in. That being said, it is really important to understand how to work through the forces of this question and I should be familiar with it.

Answer 4

The buoyant force equals the weight of the block. The weight of the block is equal to the mass of the block times acceleration due to gravity, and also equal to the density of the block times the volume of the block times the acceleration due to gravity. The buoyant force is equal to mass of the water times acceleration due to gravity, and is also equal to the density of water times of volume of water times the acceleration due to gravity. The final trick here is realizing that the volume of water equals the volume of the block of wood divided by two.

Answer 5

Any object will float if its average density is less than that of water. The whole of a ship would sync by itself, but all the air submerged beneath the water level, between the ships, lower decks, lowers the ships average density to be less than that of water. Duh.

Answer 6

Surface tension causes a liquid to form a thin but strong layer like a skin at the liquids surface. Surface tension results from cohesion, which is the attractive force that a molecule of liquid feels towards other molecules of the same liquid. On the surface, molecules only have 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 (like the foot of a water strider) then the cohesion can lead to a net upward force.

Answer 7

Cohesion is the attractive force that a molecule of liquid feels toward other molecules of the liquid. Adhesion is the attractive force that a molecule of the liquid feels toward the molecules of some other substance.

Answer 8

When cohesive forces are stronger than adhesive forces, the meniscus will convex. (Fluid crawls up the sides of the container) When cohesive forces are weaker than adhesive forces, the meniscus will be concave. (Liquid level higher in the middle than the edges) Convex meniscus are more common.

Answer 9

When cohesive forces are stronger than adhesive forces, the meniscus will convex. (Fluid crawls up the sides of the container) When cohesive forces are weaker than adhesive forces, the meniscus will be concave. (Liquid level higher in the middle than the edges) Convex meniscus are more common.

Answer 10

Fluid dynamics is the study of fluids and motion.

Answer 11

Viscosity is the resistance of a fluid to flow. Increased viscosity of fluid increases its viscous drag, which is a non-conservative force that is analogous to resistance.

Answer 12

Low viscosity fluids have low internal resistance to flow and behave like ideal fluids. Assume conservation of energy in low viscosity fluids with laminar flow. Fluids that have no viscosity are called inviscid. More viscous fluid will “lose” more energy to nonconservative forces. Viscosity should be assumed negligible on test day.

Answer 13

Laminar flow is smooth and orderly. Modeled with layers of fluid that flow parallel to each other. Turbulent flow is tough and disorderly. Turbulence causes the formation of eddies, which are swirls of fluid of varying sizes occurring typically on the downstream side of an obstacle.

Answer 14

What’s in the top image is a fluid within an invisible tube as it passes from P to Q. Flow rates at point P and point Q are the same, however, the linear speed is faster at P. This is essentially an expression of conservation of matter: if X liters of fluid pass a point and a given amount of time, then X liters of fluid must pass all other points in the system in the same amount of time. We can clearly state, without any exceptions, that flow rate (volume per unit time) is constant for a closed system and is independent of changes in cross-sectional area. This leads us to the continuity equation, which tells us that fluids will flow more quickly through narrow passages and more slowly through wider passages.

Answer 15

The continuity equation arises from the conservation of massive fluids.

Answer 16

Ask KC about this equation. I want to really understand it well. Absolute pressure, dynamic pressure, static pressure. First, the flow rate within a closed space must be constant in all points (demonstrated by the continuity equation). Second, fluids that have low viscosity and demonstrate laminate flow can also be approximated to be conservative systems: the total mechanical energy of the system is constant if we discount the small viscous drag forces that occur in all real liquids. Combining these principles of conservation gets us to the Bernoulli’s equation. Bernoulli’s equation states that the sum of the static pressure and dynamic pressure will be constant with a closed container for an incompressible fluid, not experiencing viscous drag.

Answer 17

More energy dedicated toward fluid movement means less energy dedicated towards static fluid pressure. The inverse of this is also true: less movement means more static pressure. The faster a fluid moves, the lower pressure it will have.

Answer 18

Something to ask KC. So if velocity increases, dynamic pressure increases greatly, static pressure decrease decreases. I’m finding this counterintuitive because faster moving fluids exert less pressure.

Answer 19

First, we used the continuity equation to solve for the cross-sectional area at the bathroom. We then use Bernoulli’s equation to solve for the pressure required at ground level. This equation is cumbersome but worthwhile in doing multiple times as to become comfortable with continuity equation in Bernoulli’s equation.

Answer 20

The thing about this question is to really understand gauge pressure. Gauge pressure is ambient pressure (pressure at the surface) minus atmospheric pressure. P = absolute pressure: total pressure exerted on object submerged in fluid. (P = Po+(rho)gz) Po = incident or ambient pressure (pressure at the surface) Patm = atmospheric pressure IF ATMOSPHERIC PRESSURE AND INCIDENT PRESSURE ARE EQUAL, THEN GAUGE PRESSURE EQUALS (rho)gz Where rho is density of fluid, g is acceleration due to gravity, Z is depth of the object.

Answer 21

Two ways to solve this problem: do the calculation or absorb the problem and use your intuition and know how regarding buoyancy forces. We could quickly solve this problem on test day by recognizing that the answer choices contain an outlier (A), value slightly less than the weight of the anchor (B), the weight of the anchor (C), and the value slightly higher than the weight of the anchor (D). Since buoyant force is in the same direction as tension and their sum must equal the weight of the anchor, (B) is the most likely answer. Math way:

Answer 22

This question uses the continuity equation: V1A1=V2A2 Be cognizant these problems often diameter, or radius, and I need area in the continuity equation. The equation for the area of a circle is pi r squared or pie d squared over four. Pie D squared over for method done in orange in image. Got a little stuck on the algebra here when I was faced with a whole number multiplied by a fraction squared. Remember that if you score a fraction, you square the numerator and the denominator.

Answer 23

Venturi effect: for a horizontal flow, there is an inverse relationship between pressure and speed, and in a closed system, there is a direct relationship between cross-sectional area and pressure exerted on the walls of the tube. In the picture of fluids flowing through different diameter pipes: as the tube narrows, linear speed increases at point 2 (the narrow part). Thus, pressure exerted at the walls at point 2 decreases, causing the column above point 2 to have a lower height.

Answer 24

You can zoom into the books answer above the whiteboard image.

Answer 25

Answer on page 157