Physics 3.5: Fluids

Question 1

density

Answer 1

scalar quantity and therefore has no direction

Question 2

Hydrostatics

Answer 2

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

Question 3

Pascal’s principle

Answer 3

*conservation of energy (assuming the absence of frictional forces)

Question 4

Work due to pressure and volume (fluids)

Question 5

Bouyant Force (F_bouy)

Answer 5

A body wholly or partially immersed in a fluid will be buoyed up by a force equal to the weight of the fluid that it displaces.

F_bouy=(V_{fluid displaced}) (ρ_fluid)g=(V_{object submerged})(ρ_fluid)(g)

Question 6

cohesion

Answer 6

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

Question 7

adhesion

Answer 7

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

Question 8

viscosity

Answer 8

resistance of a fluid to flow

• *Because viscosity is a measure of a fluid’s internal resistance to flow, more viscous fluids will “ lose” more energy to friction.
• The SI unit of viscosity is the newton · second/m² (N· s/m²).

Question 9

ideal fluids

Answer 9

no viscosity and are described as inviscid.

Question 10

LAMINAR AND TURBULENT FLOW

Answer 10

Laminar: smooth/orderly

Turbulant: rough and disorderly

Question 11

Critical Belocity

Answer 11

N_Ris a dimensionless constant called the Reynolds number, η is the viscosity of the fluid, ρ is the density of the fluid, and D is the diameter of the tube.

V_c=N_Rη /ρD

Question 12

streamlines.

Answer 12

streamlines indicate the pathway followed by tiny fluid elements (sometimes called fluid particles) as they move.

The velocity vector of a fluid particle will always be tangential to the streamline at any point.

Streamlines never cross each other.

Question 13

The Continuity Equation

Answer 13

tells us that fluids will flow more quickly through narrow passages and more slowly through wider ones.

v₁A₁=v₂A₂=a constant rate of flow

Question 14

BERNOULLI’S EQUATION

Answer 14

P₁ + (ρv₁²)/2 + ρgy₁ = P₂ + (ρv₂²)/2 + ρgy₂ = a constant

• energy conservation: More energy dedicated towards fluid movement means less energy dedicated towards fluid pressure.
• Newton’s second law– relates forces and accelerations: When two points within a fluid are at different static pressures, the fluid will experience a net force from the point of higher pressure to that lower pressure and will flow (and accelerate) in that direction.** **

Question 15

Elastic Properties of Solids

Answer 15

a measure of the response of a solid to an application of pressure

Moduli: Youngs, Shear, Builk

For all three moduli, a largenumber represents a more rigid material, while a small number represents a more malleable material.

Question 16

Young’s modulus, Y

Answer 16

the ratio of stress over strain

Y= (F/A)/ΔL/L)

**Yield strength **is the point of shape change beyond which a material will not return to its original dimensions once the applied force is removed (think of a crumpled piece of paper).

_ ultimate strength_ will be reached if more stress applied, beyond which point the object will rupture (think of a broken rubber band).

Question 17

shear modulus

Answer 17

S= (F/A)/(x/h)

shear: shapre change due to force applied parallel to an object’s surface rather than perpandicular to it

Question 18

bulk modulus

Answer 18

indicates the degree to which a material will experience a change in its volume in relation to an applied pressure

B=(F/A)/ΔV/V)

• speed of sound in a material is proportional to the square root of the bulk modulus of that material.
• Because gases have small bulk moduli, liquids have larger bulk moduli, and solids have the largest, sound will travel fastest through solids and slowest through gases

Question 19

Gauge Pressure

Answer 19

difference between surface pressure and absolute pressure In liquids, gauge pressure is caused by the weight of the liquid above the point of measurement

Question 20

Absolute Pressure

Answer 20

is the sum of all pressures at a certain point within a fluid; it is equal to the pressure at the surface of the fluid (usually atmospheric pressure) plus the pressure due to the fluid itself

Question 21

Pressure

Answer 21

• Defined as a measure of force per unit area;
• it is exerted by a fluid on the walls of its container and on objects placed in the fluid

It is a scalar quantity; i

• magnitude only, and no direction
• The pressure exerted by a gas against the walls of its container will always be perpendicular(normal) to the container walls

Question 22

Essential Equations: Fluids