Fluid Dynamics

Question 1

What are fluids?

Answer 1

anything that flows; exert force

Question 2

Hydrostatic pressure

Answer 2

force of fluids supporting its weight

Question 3

Describe the density of water vs air and salt water vs fresh water

Answer 3

water > air; salt > fresh

Question 4

Name two types of fluid forces

Answer 4

1. BUOYANT FORCE

2. DYNAMIC FORCE

Question 5

Buoyant force

Answer 5

ALWAYS ACTS VERTICALLY

upward force - downward force

Question 6

Specific gravity

Answer 6

ratio of weight and equal volume of water

Question 7

Archimedes Principle

Answer 7

weight = vol. of fluid displaced

Question 8

“ball rocket in water”

Answer 8

the reaction force depends on how much water is pushed out of the way. Force will act upward

Question 9

floaters vs sinkers

Answer 9

floater= object < 1.0
sinker= object > 1.0

Question 10

When an object moves within a fluid, what forces are exerted ON the object?

Answer 10

Dynamic force

Question 11

What is the most potent variable in DFF?

Answer 11

relative velocity

Question 12

Relative Velocity

Answer 12

velocity of object - fluid velocity
(+) same direction
(-) opposite direction

Question 13

What is drag force

Answer 13

acts parallel of opposite force

SLOWS DOWN THE OBJECTS RELATIVE VELOCITY

Question 14

Name 3 types of drag forces

Answer 14

1. Surface Drag
2. Form Drag
3. Wave Drage

Question 15

another name for surface drag

Answer 15

“skin friction”

Question 16

Describe fluid molecules in surface drag

Answer 16

fluid molecules slow down as they slide past the object’s surface

Question 17

What can cause surface drag?

Answer 17

• roughness of surface
• cross sectional area
• viscosity
• square of velocity

Question 18

When air temp is warm…

Answer 18

• density decreases

- viscosity increases

Question 19

At a higher altitude…

Answer 19

density decreases

Question 20

When humidity is high…

Answer 20

viscosity decreases

Question 21

In salt water..

Answer 21

density, drag, and buoyancy increase

Question 22

Object/person will travel faster and farther–

Answer 22

• in warm weather
• at higher altitudes
• on humid days

Question 23

Describe molecules in form drag

Answer 23

fluid molecules bounce off surface of object moving through it; MOLECULES WILL STRIKE OTHERS AND PUSH BACK ON OBJECT

Question 24

Laminar flow

Answer 24

molecules flow close surface to reduce form drag

Question 25

Turbulent flow

Answer 25

molecules flow past an object separate from surface * change of shape too drastic * relative velocity is too fast

Question 26

Why do cyclists draft

Answer 26

- conserves energy | - reduces drag

Question 27

Wave drag

Answer 27

interface between air&water | excessive up and down

Question 28

How to reduce wave drag

Answer 28

- swim under water as long as possible - hydroplane - gutters in pools

Question 29

how to minimize drag in general

Answer 29

SHAPE&SURFACE density CROSS SECTIONAL AREA relative velocity

Question 30

Lift force

Answer 30

acts perpendicular to motions of object NOT ALWAYS UPWARD caused by lateral deflection of molecules

Question 31

Bernouli's Principle and how it relates to lift

Answer 31

faster molecules produce lower pressure (lift) slower molecules produce higher pressure LIFT will occur in the direction of faster moving molecules

Question 32

Magnus effect

Answer 32

DIFFERENT FLOW SPEEDS ON DIFFERENT SIDES OF THE SPINNING BALL 1 side= high pressure 1 side= low pressure

Question 33

Why are bicycle helmets tapered posteriorly?

Answer 33

reduces pressure/form drag and fills in area of low pressure

Question 34

describe 3 things an athlete can do to reduce drag forces on his/her body

Answer 34

1. what they wear 2. cross sectional area 3. smooth surface

Question 35

how does the spin of a tennis ball affect its flight?

Answer 35

Magnus effect | *there are different pressures on each side of the ball as it rotates.

Question 36

name the different drag forces effected by putting dimples on a golf ball

Answer 36

form drag decreases and surface drag increases

Question 37

why do swimmers shave their bodies?

Answer 37

reduce surface drag