Mechanical Principles Midterm (test 2) Flashcards
Things that affect drag:
Increased air temp
Increased humidity
Increased altitude
All Decrease air density and drag
Drag definition
Collection of fluid forces that tend to oppose the actions an athlete is performing
Drag forces always act in opposite direction
Surface drag def
Aka skin friction or viscous drag
Drag derived from friction between the fluid Nd the object passing through the fluid boundary layer.
It is layer of air or water in direct contact with athlete
When does skin friction of surface drag increase
When relative velocity of fluid flow increases
Surface area of body over which the flow occurs increases
Increase the roughness of body surface
Increase the viscosity of fluid
Laminar flow
Smooth, parallel layers of fluid
Turbulent flow
Mixing of adjacent fluid layers and partial loss of the boundary layer
What is Form drag derived from
Aka profile drag and pressure drag
Derived from a pressure differential between the lead and read sides of a body moving through a fluid
What does the rear side of form drag create
A wake from swirling low pressure or turbulence
What does a streamlined shape due to form drag
Reduces form drag by reducing the turbulence created at the trailing edge
Form drag increases when
Increase in relative velocity of fluid flow
Magnitude of the pressure gradient between the front and rear ends of the Body increase
Surface area of the body perpendicular to the fluid flow increases
Wave drag def
Drag derived from the generation of waves at the interface between two different fluids, such as air and water
Which sports does wave drag effect?
Sports with lots of up and down movements
Breaststroke, Butterfly, boating
Wave drag wave created in front is what
A high pressure wall the resists forward movement
Wave drag increases with:
Vertical oscillation of the body with respect to fluid
Relative velocity of the body in fluid
Wave drag decreases when:
Stay under water as long as possible
Get as far out of the water as possible (hydroplane)
Wave drag in swimming
Swimmers want to make minimal wave
More prominent in open water swims
Lane lines minimized wave drag by dissipating moving surface water
Lift
A force acting on a body in a fluid in a direction perpendicular to the fluid flow
Resultant force equation
Resultant force= lift+ drag
Lift increases with
Increase velocity of fluid, surface area of flag side of foil, density of fluid
Bernoulis principle
Inverse relationship between relative velocity and relative pressure In a fluid flow
Regions of low pressure are associated with regions of high pressure
Creating lift
Bs principle + newtons 3rd law
Increased air pressure below the airfoil
Air is directed downward on the upper and lower surfaces
Magnus effect
Pressure differential created by a spinning body
Deviation in trajectory of a spinning object toward the direction of spin
What is a Fluid?
Both liquids and gases are fluids
What are fluids that commonly exert forces on the human body
air and water
Fluid Properties
Density - mass/volume
Viscosity – how thick the fluid; how much it clings
Hydrostatic Pressure def
Force exerted by a fluid (air or water)
Buoyancy def
Tendency for something to float
What direction is buoyant force?
always vertically upward, against gravity:
Example of buoyancy
torso is easier to float than legs bc more buoyant
what will happen to floating body until buoyant force and weight force are vertically aligned?
body will rotate
balance def
The ability to control equilibrium
Ability to keep the center of gravity (line or gravity) within their base of support (most of the time)
stability def
Amount of resistance used to prevent the loss of balance
Maintaining the line of gravity within the base of support
example of balance, good stability
sumo wrestler in low stance
example of good balance but bad stability
ballerina on toes
linear stability def
Resistance to being stopped or having direction changed
linear stability relation to mass
directly related. more mass more linear stability
Consequence more mass;
greater inertia to start movement and change direction
Rotary stability def
Resistance to being tilted, tipped-over, or spun
which sports use rotary stability the most?
grappling arts such as wrestling and judo
What must you maintain for rotary stability?
Need to maintain COG (line of gravity) within the base of support
The BLANK the COG is outside the base of support, the BLANK the torque gravity produces, and the BLANK it is to recover
greater greater harder
Opposing forces that jeopardize stability of rotary stabiliity
Gravity
Wind
Another body (may or may not be human)
When destabilized in rotary stability, what can be the axis of rotation?
any part of the body or the opponents body
Maximizing stability
Wider base
Lower COG
Greater mass; also greater inertia to start and change directions
where does COG’s Line of gravity (LOG) fall within
the center of base of support
When anticipating an oncoming force
shift……
COG/LOG to the edge of the base of support that is closest to the oncoming force
How do you Lower COG
Spread base of support wide in direction of oncoming force
To produce great force and or velocity in a specific direction:
Widen the base of support in the direction of the force output to aid in force output and to maintain balance.
What is going on with your stability as you are running or walking?
its oscillating between stable and unstable conditions
