Chem / Phys: Fluids

Question 1

This principle states that a change in pressure is transmitted, undiminished to all parts of an ideal (incompressible) liquid.

Answer 1

Pascal’s Principle

Question 2

Hydraulic Lifts are a common example of what principle?

Answer 2

Pascal’s Principle

Question 3

Because ideal fluids are ___ systems, allowing energy to be conserved in situations that for example, involve pumping fluids in an area between 2 pistons.

Answer 3

frictionless

Question 4

What principle states that an object that is submerged in fluid will be buoyed upwards by a buoyant force, and that the submerged portion of that object displaces an equal volume of water?

Answer 4

Archimedes’ Principle

Question 5

What force states that the mass of the displaced fluid places an upward force on the object displacing it, equal to (mass of displaced fluid)(g).

Answer 5

Buoyant Force!

Question 6

True / False: The buoyant force always opposes the force of gravity.

Answer 6

True!

Question 7

True / False: The buoyancy equation includes the density of the object submerged.

Answer 7

False! it includes the volume of the object submerged, which is multiplied by density of the fluid displaced to get the mass of the fluid displaced by the object

Question 8

If an object sinks in fluid, like a bowling ball in water, which force is greater? Buoyant or Gravitational?

Answer 8

Gravitational (net force is down, acceleration is down)

Question 9

If an object is in equilibrium, like an apple floating in water, where is the net force directing it?

Answer 9

the net force is zero and is not pulling the object in any direction ; for an apple floating in water, the buoyant force and gravitational forces are equal in magnitude

Question 10

What principle states that a molecule in the middle of a liquid sample will experience equal attractive forces on all sides of it?

Answer 10

Cohesion

Question 11

What principle states that a molecule in the surface of a liquid sample will experience greater attractive liquid forces than from the air above them? (think of it as the net force on that molecule pulling it towards the center of that liquid)

Answer 11

Cohesion

Question 12

What principle states that when liquid molecules experience greater attraction to another substance, like the surface of their container, than other liquid molecules?

Answer 12

Adhesion

Question 13

Why does water in a test tube form a convave meniscus (why does water rise up on the sides)? Explain in terms of cohesion and adhesion.

Answer 13

The water molecules are more attracted to the sides of the test tube than other water molecules. This is adhesion.

Question 14

What is apparent weight?

Answer 14

the net downward force on an object in a liquid

Question 15

A student finds a Convex Meniscus in one of their test tubes. What can they say about the cohesive / adhesive forces of that liquid?

Answer 15

the cohesive forces of this substance are greater than the adhesive forces

Question 16

If a frictional force is included, then you cannot apply Pascal’s Principle why?

Answer 16

Pascal’s Principle depends on the conservation of Energy

Question 17

This is a measure of a fluid’s internal resistance to flow, or in better terms, “how much a fluid wants to flow”. or even the internal friction of a fluid

Answer 17

Viscosity

Question 18

Which fluid has a higher viscosity: honey or air?

Answer 18

honey! think about pouring honey, or dropping something through honey, both could be done much more quickly in air

Question 19

True / False: Because ideal fluids behave conservatively, it is assumed that they have high viscosities.

Answer 19

False

Question 20

What kind of flow rate is described by Poiseuille’s Law?

Answer 20

Laminar Flow: a smooth & orderly flow (swim drafting, how fluid will flow to fill the space behind a moving object)

Question 21

When does Poiseuille’s Law become undependable?

Answer 21

when there is turbulance in the fluid ; when critical speed of the fluid is exceeded

Question 22

Moving against the flow of fluid is ____.

Answer 22

Upstream

Question 23

Moving with the flow of fluid is ___.

Answer 23

Downstream

Question 24

Which way do the upstream and downstream axes of fluid flow typically point?

Answer 24

upstream = left ; downstream = right

Question 25

When do we go from laminar (smooth) flow to turbulent fluid flow?

Answer 25

linear speed of fluid exceeds critical speed

Question 26

If there is turbulent flow, Bernoulli’s equation can / cannot be applied.

Answer 26

Cannot ; this is because energy is being dissipated in the form of “eddies” and the flow is not conservative

Question 27

The continuity equation depends on using an ideal fluid whose ___ is conserved, thus making flow rate constant at every point in the fluid.

Answer 27

Volume

Question 28

Low viscosity and laminar flow mean that energy is conserved in a dynamic fluid.

Answer 28

Yes but why

Question 29

What is Critical Speed?

Answer 29

the maximum velocity that laminar speed will still be observed (smooth fluid flow)

Question 30

Bernoulli’s Equation: what does 1/2(pv^2) stand for?

Answer 30

the dynamic pressure exerted by the fluid due to it’s movement (think of it as Kinetic Energy divided by Volume)

Question 31

What are the P’s on either side of Bernoulli’s Equation?

Answer 31

absolute pressure exerted by the fluid