Chapter 8 - Fluid Mechanics

Question 1

What are force fluids?

Answer 1

exert on objects in them or moving through tem

Question 2

What are the two types of forces applied in fluid environments? What do they do?

Answer 2

Buoyant force: Due to object’s immersion in the fluid
- related to size of object immersed in water and how much it is immersed

dynamic force: due to object’s relative motion in the fluid

Question 3

What are the two components of dynamic force?

Answer 3

Drag force and lift force

Question 4

What is pressure and the formula?

Answer 4

Weight (force) of water all around the object

P = F/A

Question 5

How is pressure different on top of an object then on the bottom of an object?

Answer 5

the pressure on the bottom of an object sumberged in water is higher than at the top.

*this is what creates buoyancy

Upward force on the bottom of a submerged object is greater than the downward force on the top becuase pressure increases with depth in a fluid. Since force = pressure x area, and pressure is higher at greater depth, the bottom experiences more pressure and thus more force

Question 6

What is buoyant Force?

Answer 6

the upward force exerted by a fluid (like water or air) on an object that is immersed in it

*acts opposite to gravity and makes things float or feel lighter in water

Question 7

𝐹𝑏 = 𝑊𝑤 what does this formula mean?

Example?

Answer 7

The buoyant force Fb acting on an object is equal to the weight of the fluid displaced Ww.

Example: A boat floats because it displaces a volumne of water whose weight equals the boat’s weight

Question 8

What is specific gravity? What is specific gravity is less then or greater then?

Answer 8

ratio of weight of an object to the weight of an equal volume of water

SG > 1 : substance is denser than water - will sink

SG < 1: substance is less dense than water - will float

SG =1: Same density as water

Question 9

What is density and the formula?

Answer 9

ratio of mass to volume

P = m/v

P in this case mean = density

Question 10

What is density? and how does the formula correlate with density?

Answer 10

Density is a measure of how MUCH MASS is packed into a certain volume.

• it tells how “heavy” or “light” a substance is

High density = lot of mass in a space

low density = little mass in a big space

Question 11

What are example of buoyancy of human bodies specific gravity?

Muscle and bones
fat

Answer 11

muscle and bones > 1.0 denser then water

fat < 1.0 = less dense than water

Question 12

What is dynamic fluid forces?

Answer 12

Exerted on object by fluid when object moves within fluid or when fluid moves past an object immersed in it

*forces exered on a body moving through a fluid (motion)

Question 13

𝐹 ∝ 𝜌𝐴𝑣2 what does this formula mean?

Answer 13

The faster an object moves through fluid, the greater the force ( since it increases with the swaure of velocity

• a larger object (greater area) experiences more force
• a denser fluid (like water vs air) creates more force

Question 14

What does dynamic fluid depend on?

Answer 14

• Velocity of the object (faster = more force)
• fluid density
• shape and surface of the object
• cross sectional area
• viscosity of the fluid

Question 15

What is drag force?

Answer 15

a resistive force a fluid exerts against the motion of an object moving through it

*acts opposite direction of the object’s motion

Question 16

What is surface drag?

Answer 16

Friction forces acting between fluid molecules and object’s surface

Question 17

How does surface drag work?

Answer 17

• fluid particles nar the object’s surface stick to it due viscosity
• as the object moves, the fluid particles near the surfaces are dragged along with it
• the fluid stickiness and the roguhness of the object’s surface causes friction which can resists motion

Question 18

What is form drag?

Answer 18

Sum of impact forces of collisions between fluid molecules and objects

*caused by the shape and size of the object relative to teh flow of the fluid

Question 19

What is the difference between surface drag and form drag?

Answer 19

Surface drag:
a drag due to friction between the surface of the object and the fluid it’s moving through

Form drag: is the drag (pressure drag) that arises due to the shape and size of an object moving through a fluid

*cause by pressure difference between the front and rear of the object which creates resistance

Question 20

How is a car streamline design help with form drag?

Answer 20

the design helps in providing less form drag than a boxy car because the streamlined shape allows air to flow more smoothly over it, reducing turbulence and resistance

Question 21

Factors of surface drag.

Answer 21

• roughness of surface, viscosity

Question 22

What is laminar flow?

Answer 22

Movement of fluid molecules in adjacent layers parallel to one another, closely following the shape of the object
*move at constant speed

Question 23

What is turbulent flow?

Answer 23

a fluid molecules moving where adjacent layers do not flow parallel and are separated from the surface of the object.

Question 24

Can turbulent flow increase drag?

Answer 24

yes

Question 25

What are ways to minimize drag?

Answer 25

- Smooth surfaces (like gear) -streamline shape (position of a body like speed skating) - faster velocities: form drag - slower velocities: surface drag *(because to reduce friction?) - reduce cross-sectional (frontal area)

Question 26

What are ways to increase drag froce?

Answer 26

paddles and oars - running with a parachute - running underwater

Question 27

what is a lift?

Answer 27

A type of force that acts perpendicular to the motion of the object. - a force that pushes the plane upwards

Question 28

What does Bernoulli's Principle say?

Answer 28

an increase in velocity of the fluid results in a decrease in pressure. A decrease in velocity results in higher pressure

Question 29

How does the Bernoulli's Principle apply to airfoils and wing shapes? How does this affect lift?

Answer 29

1) air traveling over the top of the wing has to cover a longer distance in the same amount of time, which causes it to speed up. ***** AS the air SPEEDS UP, the pressure on the top wing decreases 2) air moving under the bottom of the wing doesn't need to travel as far, so it moves slower. ***** the pressure on the bottom of the wing is higher than the pressure on the top ** these difference in pressure creates lift creating an upward force

Question 30

What is the magnus effect?

Answer 30

Spining an object cause the air on one side (where the spin is going in the same direction as the motion) move faster on the oppoiste side, the spin is going in the opposite direction of motion, airflow is slower this result in lift

Question 31

g

Answer 31

center of pressure is the point where the force acts on object moving thorugh a fluid but torqu is produced when center of pressure is not in line with the line

Question 32

Torque

Answer 32

a rotational force that causes an object to spin or rotate. If the center of pressure is not aligned with the center of gravity, a torque is generated causing the frisbeel to tilt or flip

Question 33

How are mass of object experience changes of acceleration in dynamic forces?

Answer 33

Objects with similar size and shape will experience same dynamic fluid forces, but object with more mass will experience less acceleration