Drag

Question 1

fluid mechanics

Answer 1

The natural science of fluids (liquids or gases) in motion
In some cases fluid forces have little effect on an objects motion
drag
impacts horizontially
lift
impacts vertically

Question 2

boundary layer

Answer 2

A thin layer of air surrounding or “attached” to the ball
can be laminar or turbulent

Question 3

laminar flow

Answer 3

A type of fluid flow in which the fluid move smoothly in individual streams or layers
Flow that occurs in parallel to each other

Question 4

turbulent flow

Answer 4

Flow in which the velocity at any point varies erratically
When the nice neat pattern breaks down the flow becomes turbulent
Fluid often changes from laminar to turbulent when they go over an abrupt feature like wind going over a ridgeline of a mountain

Question 5

boundary layer seperation

Answer 5

Where the boundary layer breaks away from the ball
The earlier the separation the greater the pressure gradient between the front and back of the ball which leads to more drag

Question 6

factors affecting boundary layer separation point

Answer 6

velocity
surface roughness
shape

Question 7

velocity

Answer 7

○ Low velocity
§ the boundary layer clings to the surface so separation occurs well towards the rear
□ This results in minor drag
○ High velocity
§ Separation occurs further forward
This results in increased drag

Question 8

surface roughness

Answer 8

○ Rough surfaces create turbulent boundary layers, which reduces the affect of drag
§ Dimpled golf ball vs smooth
Swimsuits are designed to have rough surfaces

Question 9

shape

Answer 9

§ the boundary layer clings to the surface so separation occurs well towards the rear
□ This results in minor drag
○ Round ball
§ Separation occurs further forward
This results in increased drag

Question 10

lift/drag - fluid resistance relationship

Answer 10

lift = y
drag = x
fluid resistance: y=x

Question 11

fluid resistance

Answer 11

• As an object moves through a fluid, it disturbs it
  The greater the disturbance to the fluid, the greater the transfer of energy from object to fluid

Question 12

factors that affect fluid resistance

Answer 12

○ Density (air)
§ The denser the fluid, the more disturbed it becomes and hence the greater the resistance
○ Viscosity (liquid)
§ The more viscous the fluid the more disturbed it becomes and hence the greater the resistance
Swimmer vs runner

Question 13

types of drag

Answer 13

surface drag
form drag
wave drag

Question 14

surface drag

Answer 14

• The friction produced between a fluid and the surface of a moving object
  
  • Factors affecting surface drag
    ○ Relative velocity to moving object
    ○ Relative roughness of surface object
    ○ Viscosity of the fluid
    ○ Surface area of the object

Question 15

form drag

Answer 15

• The resistance created by the pressure differential between the front and the back of an object travelling through a fluid
  
  • Factors affecting form drag
    ○ The cross sectional area of the object presented to the fluid
    ○ Velocity of the object
    ○ Surface roughness
    ○ Shape of the object

Question 16

wave drag

Answer 16

• The creation of waves forms resistance at the point where air and water interact
  
  • Seen as the major form of drag affecting swimmers
  • Factors that affect wave drag
    ○ Relative velocity of the wave
    ○ Technique
    swim lower = less
    ○ Open water vs closed conditions (ocean vs pool)
    Lane ropes are used to reduce wave drag by helping dissipate waves through the surface of the water

Question 17

factors affecting drag

Answer 17

Drag coefficient
○ Measure used to quantify the drag or resistance of an object in a fluid environment
○ Directly related to cross sectional area

Mass
○ The greater mass of the ball the less effect of drag

Velocity
○ The faster the ball moves through the air, the earlier the boundary layer separates from the ball, creating a large pressure differential between the front and rear of the ball hence more drag

Surface roughness
○ Rougher surfaces allows the air stream to cling to the ball for longer periods of time, resulting in a smaller pressure differential and therefore less drag

Cross sectional area
○ A linear relationship exists between CSA exposed to fluid and drag

Shape
○ Round ball vs oval ball
○ NFL ball cuts through air more cleanly than a soccer ball
Oval shape encourages air to cling to surface all the way to the end of the tail meaning smaller pressure differential and less drag