Lecture 27 - Aerodynamics in Sports Flashcards
What is drafting?
- when you stay in the person in front of you streamline, you experience less drag because you don’t have to break the air in front of you
- you are in a low-pressure wake meaning you experience less drag
- elite athletes do it (therefore it’s right)
what is drag coefficient?
- C drag
- dependent on body position (more cross-sectional area = higher drag force) –> because larger wake behind you
what is the projection angle?
- angle between the velocity vector and the horizontal ground
- the way the object is actually going
what is the angle of attack?
- the angle between oncoming flow and the angle of the body (related to lift)
- between the velocity vector and object orientation?
what is the attitude angle?
- the angle between the object orientation and the horizontal ground
how are projection angle, angle of attack and attitude angle related?
- positive attitude with negative projection angle has a positive angle of attack (imagine landing a plane)
- uses 3 lines and three different combinations to find 3 different angles
how do attitude angle and velocity change with a parabolic flight?
- if the pathway isn’t straight, the velocity follows tangent to the pathway
- the projection angle is always changing
- the attitude angle may or may not change
what does an attitude angle pointing up imply?
- the object is experiencing lift for longer
what is the center of pressure?
- the combined effect of the forces add up to act on the center of pressure
- the air applies force to the entire “wetted” surface of the object
how does CP relate to CM?
- they are usually not in the same spot
- CP usually causes torque by drag force to make the object rotate around the CM
where does gravity act in an object?
- on the CM (center of mass)
where do drag and lift act on an object?
- on the CP (center of pressure)
if the air force pulls upwards and the CP is in front of the CM, will the resultant be nose up or nose down?
- nose up
what is the vertical velocity of an object at the peak?
- none
- no projection angle (completely horizontal)
how can you calculate the angle of attack?
- attitude angle - projection angle = attack angle
- rearrange depending on what you are given
what causes a nose up rotation?
- the center of pressure in front of center of mass
- with upwards attitude
- CP moves behind CM as angle of attack lowers (end of flight) –> nose down
how do ski jumpers make sure lift force works for them?
- creating an angle of attack
what is the magnus effect?
- due to rotation, one side is moving faster than the other relative to the flow, the faster side experiences lower pressure so lift occurs/acts there
- causes backspins/curveballs
- rotating with flow = low pressure, rotating against flow = high pressure
what is Bernoulli’s theorem?
- increase in velocity = decrease in pressure
what is the result of the magnus effect in a slider/top spin?
- pulls the ball downward faster than gravity
- (forward spin)
- magnus force = down
what is the result of the magnus effect in a back spin?
- keep the ball up longer
- magnus force = up
what is the result of the magnus effect in a curveball?
- magnus force = sideways
- rotating on a vertical axis (spin basketball on finger)
- high pressure one side, determine right angles to see where ball will go
in golf, what is a slice?
- unintentional spin on ball
- clockwise spin if right handed
- controlled version of this is a fade
in golf, what is a hook?
- unintentional spin on the ball
- counterclockwise if right-handed
- controlled version of this is the draw