Fluid Mechanics in Physical Activity

Fluid Mechanics = study of objects that TRAVEL THROUGH a FLUID (liquid/gas)

Minimising AR/ Fluid Friction MAXIMISES VELOCITY

Fluid Friction = OPPOSES MOTION through fluids which INHIBITS VELOCITY

Factors affecting AR/ Fluid Friction/ Drag:

• VELOCITY - High velocity = High AR
• Frontal cross-sectional AREA - High Area = High AR
• SURFACE - Rough = High AR
• TEMP - High Temp (low density) = Low AR
• ALTITUDE - High Altitiude (low density) = Low AR

• Streamlining creates a SMOOTHER AIR FLOW around an object by REDUCING the bodies frontal cross-sectional AREA
• AEROFOIL = most streamlined shape with a curved upper surface & flat under surface

• Body launched into the AIR subjected to WEIGHT and AR forces
• NOT affected by FRICTION and REACTION forces
• Flight path = affected by WEIGHT of object & amount of AR experienced

PARABOLA = UNIFORM curve that is SYMMETRICAL about its highest point

• W > AR = PARABOLIC (E.g. Shot put)
• AR > W = NON - PARABOLIC (E.g. Shuttlecock)

AR becomes dominant when:

• High VELOCITY
• Large Frontal cross-sectional AREA
• ROUGH surface
• LOW mass

• Direction of motion = reflects Parabolic or Non-Parabolic nature
• AR OPPOSES motion & acts from the COM
• Weight acts DOWNWARDS from COM

GREATER velocity, area & roughness = High AR

(E.g. Shuttlecock = HIGH velocity & roughness with LOW wieght)

GRAETER mass = High WEIGHT

(E.g. Shot put = HIGH weight with LOW velocity, area & roughness)

• Calculates the NET force acting on body in FLIGHT
• Net Force = SUM of all FORCES acting on a body
• Net Force represents ACCELERATION of a body & in which DIRECTION

If Net Force arrow is CLOSER to WEIGHT = W > AR (Parabolic flight path)

If Net Force arrow is CLOSER to AR = AR > W (Non-Parabolic fight path)

In drawing inlude:

• DIRECTION of motion
• AR OPPOSES motion from COM
• Weight acts DOWNWARDS from COM
• Use dotted line to complete diagram
• SOLID DIAGONAL arrow represents Net Force

Lift Force = acts PERPENDICULAR to the DIRECTION of travel of an object in a fluid

Angle of Attack = angle at which a projectile is TILTED from the HORIZONTAL

                         = most lift force occurs at 17 DEGREES

Bernoulli Principle = molecules in a fluid exerts LESS pressure the FASTER they travel

                              = molecule in a fluid exerts MORE pressure the SLOWER they travel

How does it work?

• Lift force is present when projectiles adopt an AEROFOIL shape
• ANGLE of attack affects the SIZE of the LIFT force
• GREATER the ANGLE = GREATER LIFT force (until 17 DEGREES)
• Air will travel FURTHER over the object
• Air travel at a HIGH VELOCITY to combat distance
• Creates area of LOW PRESSURE above the object
• Creates PRESSURE GRADIENT = LIFT force (object travels FURTHER in air)