4.4 Fluid Mechanics Flashcards
Fluid mechanics
Study of how an object or the human body that travels through any liquid or gas
Drag Force
Force that acts in opposition to motion that slows things down
2 types Surface and Form
Surface drag
Friction between the surface of an object and the fluid environment
Smooth surfaces reduces friction decreasing drag & increasing velocity
Form drag
Impact of the fluid environment on an object
The forces affecting the leading edge of an object increases form drag
The forces affecting trailing edge reduce form drag
Relates to streamlining
How does form drag make cycling in a splitstream easier?
Form drag offers less turbulent air for anything in the split stream
The cyclist (if less than 30cm away) uses the air pocket and uses up to 30 % less energy
Streamlining
Shaping a body so it can move as effectively and quickly through a fluid as possible
Factors that reduce and increase drag
The velocity of a moving body
The cross-sectional area of a moving body
The shape and the surface characteristics of a moving body
The velocity of the moving body
The greater the velocity the greater the drag force through a fluid
Air resistance also increases drag
The cross sectional area of a moving body
The larger the cross sectional area the amount of drag increases
Cyclists crouch low over the handle bars to reduce their csa
The shape and surface of a moving body
Streamlined, aerodynamic shape reduces drag
Speed skiers wear aerodynamic boots and form fitting suits
Cyclists wear areodynamic helmets with air ducts
Swimmers shave their bodies and wear bodysuits with a smooth surface
The Bernoulli Principle
Upward lift
Increase in the speed of a fluid occurs as a result of a decrease in pressure
A discus (airfoil shape) experiences upward lift force during flight increasing the horizontal distance it travels
Air that travels further, travels at a faster velocity creating low pressure and air that travels a short distance travels slower creating high pressure
Pressure gradient creates upward lift
Lift
Causes a body to move perpendicular to the direction of travel
Angle of attack
The tilt of a projectile relative to the air flow
For a discus the optimum angle is 25-40 degrees. Any higher and drag increases causing the discuss to stall.
Bernoulli Principle
Downward lift
Increase in the speed of a fluid occurs as a result of a decrease in pressure
Required by speed skiers, cyclists and racing cars, by pushing the object/body into the ground, greater frictional forces are created
F1 - spoiler angled so lift force acts in a downward direction maintaining tyres firm grip onto the track around corners
Cyclists- streamlined body position keeps firm grip on the track
