Quiz #5

Question 1

What is a fluid?

Answer 1

Substance with no fixed shape
Yields easily to external pressure
A gas or (especially) a liquid

Ex. Air, water

Question 2

What are the 2 types of forces exerted on an object by a fluid environment?

Answer 2

Buoyant force

Dynamic force

Question 3

Buoyant force:

Answer 3

Due to immersion in water

Equal to weight of the volume displaced by the object

Upward force equal in magnitude to the weight of water displaced by the immerse object

Question 4

Dynamic force:

Answer 4

Due to relative motion in a fluid

Question 5

2 types of Dynamic forces:

Answer 5

Drag force

Lift force

Question 6

Drag force:

Answer 6

Acts in opposition to the relative motion of the object with respect to the fluid

X-axis component of the resultant dynamic fluid force

Question 7

Lift force:

Answer 7

Acts perpendicular to the relative motion of the object with respect to the fluid

Question 8

Balance of forces (buoyant force and weight):

Answer 8

Object sinks: weight > buoyant force
Object floats: buoyant force > weight
Object hovers: weight = buoyant force

Question 9

Floating is determined by:

Answer 9

Volume of object immersed

Weight of the object compared to the weight of the same volume of water

Question 10

What affects drag force?

Answer 10

Surface smoothness (surface drag)
Cross-sectional area (form drag)

Question 11

Surface drag:

Answer 11

A.K.A skin friction or viscous drag

Friction between the object’s surface and the fluid:
-Boundary layer of fluid has lowest velocity
-Slowed down by friction
-Dependent on the smoothness of object’s surface and
amount of surface area
-Skin, clothing

Question 12

Form drag:

Answer 12

More significant effects than surface drag

AKA Shape or Pressure Drag

Molecules bounce off object and strike other fluid molecules
-Molecules are pushed back into the object

Molecules follow the curvature of the object’s surface as the object moves past it

Laminar/Turbulent flow

Question 13

Laminar flow:

Answer 13

Fluid moving toward the object

Ordered into layers

Question 14

Turbulent flow:

Answer 14

Fluid moving when adjacent layers do not flow parallel to one another

Separate from the surface of the object in a fluid

Question 15

How do we minimize drag in sport?

Answer 15

Reduce the area of the object that touches the fluid

 - Less fluid molecules collide with the object
 - Pointed leading edge
 - Swimsuits

Question 16

Wave drag:

Answer 16

Present at interface of water and air

Wave pushes back against swimmer
-Other waves form around swimmer due to pressure
differences

Question 17

Magnus effect:

Answer 17

Lift force caused by a spin

Pressure difference on opposite sides of a ball result in topspin or backspin

Question 18

Bernoulli’s Principle :

Answer 18

Fast-moving fluids exert less pressure laterally than do slower-moving fluids

Fast relative velocity = ↓ pressure
Slow relative velocity = ↑ pressure