B.2.2 Fluid Mechanics

3 stages of projectile motion

• Initial velocity - affects both height and range

• angle of projection - determines height and accuracy

• height of release - higher release increases flight time and range

Projectile

• any object propelled into the air where only gravity and air resistance act on it

• centre of mass follows a parabolic path even if body segments move mid-flight

Environmental conditions

• external factors affect air and water density, changing the force on objects

External environmental factors

• rising temperature decreases density, decreases drag, and causes projectiles to travel further

• rising humidity decreases air density and drag

• lower air pressure lowers drag and causes longer flight distances

• higher salinity increases buoyancy

Laminar air flow

• air flow is smooth, layers don’t mix and separates early so more form drag

Drag Forces

• drag opposes motion of body through a fluid (air or water)

• total drag = surface drag + force drag + wave drag

Types of drag

• surface drag (skin friction) - depends on velocity, surface area, and smoothness

• form drag (pressure drag) - depends on shape, frontal area, velocity

• wave drag - only in water at surface and increases with speed and wave size

Example of drag reduction

• swimmers wear smooth suits to cut surface drag and streamline body to reduce form drag

Air resistance

• opposes motion which affects shape and distance of flight path

• light objects are more affected by air resistance

• heavy objects resist drag and follow more symmetrical trajectories

Flight path

• high velocity means more drag and faster deceleration so shorter range

Turbulent air flow

• air flow is more swirly with mixed layers that separate later so less form drag

drag reducers in sport

• rough surfaces can trigger turbulence to reduce drag like dimples on a golf ball

Centre of mass

• point which an objects mass is evenly distributed

• determines stability, the axis of rotation and trajectory

• centre of mass can be outside the body (high jump)