fluid mechanics Flashcards
fluid mechanics
object travelling through liquid or gas
drag force
a force that acts in opposition to motion and has negative effect on velocity (slows something down)
(fluid)
what is a drag force produced by
air resistance and friction
2 types of drag
- surface drag
2. form drag
surface drag
friction between the surface of an object and the fluid environment
form drag
impact of the fluid environment on an object
- The forces affecting the leading edge of an object increases form drag and the forces affecting trailing edge reduces form drag
- relates to streamlining and slipstream
streamlining
involving shaping a body so it can move as effectively and quickly through a liquid as possible
factors that reduce and increase drag (same as air resistance)
- velocity of moving body = greater the velocity the greater the drag
- cross sectional area = greater the CSA the greater the drag e.g. cyclists lean over handlebars
- shape and surface characteristics = clothing with ridges and aerodynamic helmets
the bernoulli principle
when air molecules exert less pressure the faster they travel and more pressure when slower
lift force
causes a body to move perpendicular to the direction of travel (allows discus to stay in the air for longer increasing the horizontal distance)
angle of attack
the tilt of a projectile relative to the air flow
how is lift achieved?
when different air pressures act on an object
optimum angle of attack for discus
25-40 degrees
explain movement of a discus
AOA changes flow of air around discus so air on top has longer distance than below. Air above travels at a faster velocity which creates lower pressure causing an upward lift force. If AOA is too great then lift is reduced and drag increases
- air tries to move from high to low pressure causing a lift force
explain movement of formula 1 sports cars
spoiler is angled so the lift force can act in a downward direction to push the car into the track. Air that travels above has a shorter distance than below due to the angle of the spoiler. Air above travels at a slower velocity at a higher pressure which creates a greater frictional force so tyres grip onto track
movement of cyclists
low streamlined position means that air travels a shorter distance above and longer below. Air above travels at a slower velocity at a higher pressure which creates a greater frictional force so tyres grip onto track
movement of speed skiers
need to stay in contact with the ice for faster speed because more downward acting lift means more force which melts the snow for friction free surface
