Fluid mechanics

Question 1

What are the two types of forces exerted by fluids?

Answer 1

Buoyant force and dynamic force

Question 2

What is fluid mechanics?

Answer 2

The study of forces that fluids exert on objects moving through them

Question 3

What is buoyancy force?

Answer 3

• Due to immersion of the object

- pressure from water weight above, beside, below

Question 4

what is dynamic force?

Answer 4

• Due to relative movement of the fluid

- Drag force, lift force

Question 5

what happens when you submerge an object deeper and deeper?

Answer 5

increase in above and below pressure

Question 6

equations for buoyancy force?

Answer 6

R lower - R upper = Buoyant force

Question 7

which is always higher, R lower of R upper?

Answer 7

R lower

Question 8

what is archimede’s Principle?

Answer 8

the buoyancy force will always equal the water weight displaced… weight always equals object in the end

Question 9

how does buoyant force affect an object?

Answer 9

buoyant for will always act up on the object, related to weight of fluid displacement.

Question 10

how can you determine if an object will sink or swim?

Answer 10

difference between the buoyant force and weight of the object

Question 11

what happens when the buoyant force is equalled to the weight ?

Answer 11

static equilibrium

Question 12

what happens if BF is bigger than mg?

Answer 12

the object will rise

Question 13

what happens if the BF is smaller than mg?

Answer 13

The object will sink

Question 14

what is density?

Answer 14

the amount of matter in a given volume

Question 15

equation for density?

Answer 15

P = m/v

Question 16

what is muscles density in respect to water?

Answer 16

1000kg/m^3, more dense than water… will sink

Question 17

what is fats density in respect to water?

Answer 17

less dense than water… will rise… olive oil on water

Question 18

where does the buoyancy act on a body?

Answer 18

centre of volume

Question 19

where does force of gravity act upon a body?

Answer 19

centre of mass

Question 20

what is dynamic fluid force?

Answer 20

force due to relative motion

Question 21

what is dynamic fluid force affected by?

Answer 21

• density of fluid
• SA of object
• (relative velocity)^2

Question 22

what is the most important in determining fluid forces?

Answer 22

relative velocity

Question 23

what is relative velocity?

Answer 23

difference between objects velocity and fluids velocity

Question 24

what is drag force?

Answer 24

component of fluid force that opposes (parallel/opposite direction) the relative motion of object

Question 25

what is surface drag?

Answer 25

sum of fiction forces acting between fluid molecules on surface and object

Question 26

what is form drag?

Answer 26

how fluid molecules travel around an object due to the objects shape

Question 27

what is skin friction/viscosity drag (surface drag)?

Answer 27

• molecules slide past object’s surface, friction creates layer called boundary layer

Question 28

what can a swimmer do to minimize friction of boundary layer?

Answer 28

minimize surface drag by shaving and using swim caps

Question 29

what is surface drag affected by?

Answer 29

• coefficient of drag (roughness of fluid and viscosity of fluid)
• fluid density
• objects cross section
• relative velocity ^2

Question 30

what is the fluid travelling around a smooth object called?

Answer 30

Laminar flow

Question 31

what does the divergence of fluid depend on?

Answer 31

shape of object

Question 32

what does converge of fluid depend on?

Answer 32

natural flow of rebalance pressure

Question 33

what is form drag produced by?

Answer 33

shape and size of object

Question 34

what is fluid pressure like when object passes it?

Answer 34

high pressure in the front, low pressure in the back

front pressure slows down object and back pressure pulls object (both slowing down object)

Question 35

what is the ideal shape than minimizes form drag?

Answer 35

shape that cuts through fluid and slowly allows fluid to recreate original trajectory

Question 36

what is form drag affected by?

Answer 36

• shape of object
• drag coefficient
• density of fluid
• cross section of object
• relative vel ^2

Question 37

why are there dimples on a golf ball?

Answer 37

dimples diminish form drag by changing laminar flow, holding molecules closer to the mall

Question 38

what is lift force?

Answer 38

dynamic force component that acts perpendicular to motion of object

Question 39

what is lift force caused by?

Answer 39

lateral deflection of fluid molecules

Question 40

how does deflection work?

Answer 40

object exerts lateral force on molecules, molecules do the same but opposite direction, causing lift

Question 41

what is lift force proportional to?

Answer 41

lateral acceleration of fluid molecules and mass of molecules

Question 42

what can alter lift force?

Answer 42

shape of object

Question 43

what is the Magnus effect?

Answer 43

air flow on an object causing spin

Question 44

what is bernoulli’s principle?

Answer 44

• fast fluid exert less force than slow fluid

ball spinning in direction of fluid is less pressure. vice versa.

Question 45

what happens to spinning a ball?

Answer 45

changes relative velocity of fluid on that object (magnus effect)

Question 46

what is topspin?

Answer 46

molecules on the top slow down due to friction as bottom molecules don’t change speed. therefore more pressure on the top, net downward. Vice versa for backspin.