1	Chapter 6 Fluids
2	Hydrostatic Pressure Hydrostatic Pressure is the force exerted by the fluid, like air or water. The air has weight, and is like blankets wrapped around the earth. At Sea Level air weighs about 14.7 pounds per square inch. That is about 1000 pounds on your head.
3	At Altitude Barometric Pressure Drops At sea level, the barometric pressure is 760 mm Mercury. At a mile high it drops to 630 mm Hg At 13,000 ft. it drops to 460 mm Hg At the top of Mt. Everest, 29,000 ft. it drops to 230 mm Hg.
4	With an Increase in Altitude there is a decrease in Oxygen At Sea Level we get about 159 mm Hg of PO₂ At 10,000 ft. it drops to 110 mm Hg At 16,000 ft. it drops to 85 mm Hg At 29,000 ft. (Mt. Everest) it drops to 48 mm Hg. Have you ever been above 10,000 ft.?
5	Water is more Dense than Air One cubic foot of salt water weighs more than one cubic foot of fresh water. As one goes under water the pressure rises much faster than air would. At a depth of 33 ft. the pressure increases by one atmosphere, which means that there is 2 atmospheres of pressure on the person, or 29.4 psi.
6	"At a depth of 66..." At a depth of 66 ft. the pressure increases to 3 atmospheres, or 44.1 psi At 99 ft. it increases to 58.8 psi The body can tolerate a lot of pressure but the cavities, inner ear, nasal sinuses, lungs, have to be balanced with the the water pressure. A liter of air at the surface shrinks by the depth: ½ at 33 ft., 1/3 at 66 ft., ¼ at 99 ft.
7	When Surfacing after Being at Depth the air expands At depth one breathes highly compressed air If the lungs have 3 liters of air at depth, it doubles its volume for every 33 ft. the body rises from the depth. Also, the air and particularly Nitrogen which had been dissolved in the blood, will bubble up in the blood if the person rises too rapidly, so they constantly exhale during ascent.
8	Buoyancy Related to hydrostatic pressure and pushes the body upward against gravity. The buoyancy force acting on an athlete’s body is equal to the weight of the water displaced by the body. As the athlete gets more of their body in the water the buoyancy force increase until the athlete is fully submerged.
9	"When the buoyancy force is..." When the buoyancy force is greater than the weight of the object, the object will rise in the water, or is pushed to the surface (it floats).
10	Body Types and Buoyancy A person with big bones, and massive muscles with little body fat is denser than the person with lots of body fat, and less muscle mass. Bone and muscle are denser than water and will sink. Fat is not as dense as water and will float
11	"English Channel Swimmers have large..." English Channel Swimmers have large amounts of body fat. This gives them more buoyancy force, more insullation, and more energy stores.
12	"A divers wet suit is..." A divers wet suit is made from foam rubber and has very little density. A heavily muscled athlete with body density greater than water will float with the wet suit on. As the diver descends in the water the compressive forces make the wet suit more dense, and it loses some of its buoyancy.
13	"To balance the reduction in..." To balance the reduction in buoyancy force from the compressed wet suit the diver blows air into a vest that helps the diver control their weight in the water.
14	Buoyancy Forces Vary With differences in water density The more dense the water the greater the buoyancy forces With differences in temperature. The higher the temperature the less dense the water.
15	Center of Buoyancy The center of buoyancy is the center of volume of the water displaced. The body has its largest volume in the thorax, however since most of the thorax is air filled lungs, the buoyancy force is greater on the thorax, than the legs where there is not as much volume but dense muscles and bones.
16	Floating Position Since the thorax has much volume but not much density, the buoyancy force pushes this part of the body upward. However, the legs are much denser than the thorax and will sink. The CG and the Center of Buoyancy are not the same, with the CB usually more superior in the body than CG.
17	"Figure 6.3" Figure 6.3
18	Drag Drag varies according to the: Type of fluid; water or air Temperature of the fluid Density of the fluid Viscosity (thick or thin) Size and shape of the athlete or object Surface of the athlete or object Velocity of the object or body relative to the airflow
19	"Relative motion Fig." Relative motion Fig. 6.5
20	Characteristics of air and water Both have density, but air is not as thick, dense or sticky as water Temperature, pressure, and what is in the fluid (like water in the air or salt in the water). Air temperature: the he warmer the air the thinner the air, density decreases. Barometric pressure: as air pressure increases so does the resistance of the air against moving objects, or as one gets higher in altitude the pressure decreases and so does the air resistance against the body.
21	"As humidity increases air resistance..." As humidity increases air resistance decreases as humidity increases oxygen and nitrogen molecules are replaced by lighter water water molecules, making humid air less dense when humidity changes to precipitation and the water is no longer in vapor form but liquid form and the resistance to moving objects increases. A baseball or golf ball will travel farther and faster in warmer air, at higher altitudes in humid air. Curve balls and knuckleballs need thicker air so that the air resistance causes the curves. Fastball goes faster at higher altitudes, as well as a cyclist, sprinter.
22	Fluid Viscosity measure of fluid flow or the fluid's stickiness and ability to cling to an object. Viscosity decreases slightly with an increase of temperature.
23	Surface Drag Surface drag combines with Form drag and Wave drag. Surface drag; viscous drag or skin friction boundary layer
24	Form drag Shape drag, profile drag, and pressure drag as one pushes through the air it causes turbulence to occur behind the object This is called wake and is an area of turbulence, low pressure and suction Amount of this drag depends on the high pressure in front, and the low pressure behind. The greater the difference the greater the drag
25	Figure 6.6
26	Efforts to reduce form drag and surface drag Body positions Eliminate bumps, projections and rough edges Smooth surfaces Fill in area at rear where the low pressure wake occurs streamline tear drop effect Spokes of front wheel on bicycle filled in. recumbant cycling Shell covers for cyclists and human powered vehicles and planes
27	Figure 6.7
28	Making use of the wake Drafting; second cyclist can go the same speed as the lead cyclist but expends less energy
29	Flights of balls Balls are blunt and produce considerable drag Bboundary layer flows smoothly over a smoothed surface ball At low velocities the laminar flow stays pretty much together As velocity increases the laminar flow breaks up and causes turbulence.
30	Figure 6.9 Laminar Flow and 6.10 Turbulent Flow
31	"As speed of ball increases..." As speed of ball increases and as the fluid flow becomes totally turbulent the place where the laminar flow separates from the ball gets further to the front Results in a larger wake area.
32	Figure 6.11
33	At Extremely High Velocities As the velocity increases further, above Figure 6.11, the place where the boundary layer separates from the ball shifts back to the rear and reduces the size of the low pressure wake.
34	Figure 6.12
35	Dimples Reduce Form Drag Dimples on a golf ball, as well as, fuzz on a tennis ball, and seams on a baseball or softball causes a turbulent boundary layer to form all around the ball – even at slower velocities than smooth balls. Although the surface drag is increased the form drag decreases, as well as the total drag
36	Wave drag When two fluids meet, water and air, produces waves which cause additional resistance to movement. At competitive speeds wave drag is greater than form or surface drag Surface and form drag increase by the square of the velocity Wave drag increases by the cube of the velocity Pool design can reduce waves Swimming longer underwater and hydroplaning reduce wave drag
37	Lift Two forces: one acting in the direction of the air flow, and the other acting perpendicular to the drag forces Drag and lift combine to produce a resultant force that most commonly pushes upward and backward.
38	Bernouli’s Principle: Figure 6.18
39	Figures 6.13
40	Figure 6.14
41	Angle of Projection – Between V and Hor. Angle of Attack – Between V and Attitude Angle of Attitude – Between Plane of Discus and Hor.
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44	Angle of Attack As angle of attack increases the greater the drag and lift up to a point where the lift disappears and the object stalls Lift increases when air or water is denser
45	Ski jumping, Fig. 6-15
46	Downward lift In auto racing where front and rear spoilers are angled to push car downward and increase friction to get better traction.
47	Figure 6.17
48	Lift and drag as propulsive forces Bernouli's principle; airfoil Swimmer's hand
49	Figure 6.20
50	The magnus effect: Fig. 6.25
51	"Top view of a pitch" Top view of a pitch Curve Ball Magnus Force to the left. Drag force opposite V of ball Resultant of Magnus F and Drag
52	Top spin produces a Magnus Force Pushing the Ball Downward
53	Backspin Produces an Upward Magnus Force which Keeps the Ball Up Longer