Lecture 27 - Aerodynamics in Sports

Question 1

What is drafting?

Answer 1

• 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)

Question 2

what is drag coefficient?

Answer 2

• C drag
• dependent on body position (more cross-sectional area = higher drag force) –> because larger wake behind you

Question 3

what is the projection angle?

Answer 3

• angle between the velocity vector and the horizontal ground
• the way the object is actually going

Question 4

what is the angle of attack?

Answer 4

• the angle between oncoming flow and the angle of the body (related to lift)
• between the velocity vector and object orientation?

Question 5

what is the attitude angle?

Answer 5

• the angle between the object orientation and the horizontal ground

Question 6

how are projection angle, angle of attack and attitude angle related?

Answer 6

• 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

Question 7

how do attitude angle and velocity change with a parabolic flight?

Answer 7

• 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

Question 8

what does an attitude angle pointing up imply?

Answer 8

• the object is experiencing lift for longer

Question 9

what is the center of pressure?

Answer 9

• 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

Question 10

how does CP relate to CM?

Answer 10

• they are usually not in the same spot
• CP usually causes torque by drag force to make the object rotate around the CM

Question 11

where does gravity act in an object?

Answer 11

• on the CM (center of mass)

Question 12

where do drag and lift act on an object?

Answer 12

• on the CP (center of pressure)

Question 13

if the air force pulls upwards and the CP is in front of the CM, will the resultant be nose up or nose down?

Answer 13

• nose up

Question 14

what is the vertical velocity of an object at the peak?

Answer 14

• none
• no projection angle (completely horizontal)

Question 15

how can you calculate the angle of attack?

Answer 15

• attitude angle - projection angle = attack angle
• rearrange depending on what you are given

Question 16

what causes a nose up rotation?

Answer 16

• 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

Question 17

how do ski jumpers make sure lift force works for them?

Answer 17

• creating an angle of attack

Question 18

what is the magnus effect?

Answer 18

• 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

Question 19

what is Bernoulli’s theorem?

Answer 19

• increase in velocity = decrease in pressure

Question 20

what is the result of the magnus effect in a slider/top spin?

Answer 20

• pulls the ball downward faster than gravity
• (forward spin)
• magnus force = down

Question 21

what is the result of the magnus effect in a back spin?

Answer 21

• keep the ball up longer
• magnus force = up

Question 22

what is the result of the magnus effect in a curveball?

Answer 22

• 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

Question 23

in golf, what is a slice?

Answer 23

• unintentional spin on ball
• clockwise spin if right handed
• controlled version of this is a fade

Question 24

in golf, what is a hook?

Answer 24

• unintentional spin on the ball
• counterclockwise if right-handed
• controlled version of this is the draw