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# Biomechanics 4

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Projectiles and Fluid Mechanics

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### Biomechanics 4

1. 1. Biomechanics 4
2. 2. Learning Outcomes Be able to: • Name 3 things that effect how far a projectile travels horizontally • Explain what effects the optimal angle of release • Explain what a parabola flight path is and what causes deviations from parabola flight path. • Apply the Bernoulli Principle to a sporting situation • Explain the Magnus effect with relation to the spin placed on an object in flight.
3. 3. Projectile motion
4. 4. Projectiles e.g. • Athlete who propels themselves in to the air such as high jumper or long jumper in athletics • Object hit, thrown or kicked in to the air such as shot put, badminton shuttle, football • When an athlete breaks contact with the ground or objects are released, they become projectiles
5. 5. Release of projectiles Three factors effect the horizontal distance a projectile travels: • The angle of release • The velocity at release • The height at which released
6. 6. Optimal angle of release Depends on - release height & landing height RH>LH Optimal angle<45degrees E.g. Shot put RH = LH Optimal angle = 45 degrees E.g. Lofted pass in football RH<LH Optimal angle> 45degrees E.g. Bunker shot in golf
7. 7. Task 1 With a partner decide whether the optimum angle of release is equal to, less than or greater than 45 degrees. • Racing dive in swimming • High jump • Hockey flick/scoop • Long jump • Tennis serve
8. 8. Velocity of release Increase release velocity to increase horizontal distance travelled E.g. •Speed at run up for Long Jump •Speed of rotation on hammer throw
9. 9. Height of release Consider two shot putters Providing angle and velocity of release the same for both, the taller shot putter will achieve a greater distance because of height of release.
10. 10. Projectiles and forces in flight Projectiles that have a large weight force and small air resistance force e.g. shot puts, follow paths close to a true parabola.
11. 11. Deviations from parabolic flight path • Objects travelling at high speeds e.g. golf balls • Objects that have large cross sectional area e.g. footballs • Objects that do not have a smooth surface e.g. badminton shuttle ………all these incidents have distorted parabola. ……….the golf ball will follow a flight path closer to a true parabola than a table tennis ball because it is heavier
12. 12. Task 2 • Using the text books and iPads investigate how the “Bernoulli Principle” and the “Magnus Effect” affect the flight path of an object • And produce a short presentation using Explain Everything.
13. 13. Projectiles and lift If projectile can gain some lift during flight, it will stay in the air longer and achieve a greater horizontal distance. Best way to introduce this is to think of an aeroplane wing and how this works. Rounded shape pushes air over it and makes it travel further than air underneath the wing. Fast flow – pressure low Bernoulli Principle Thought: Formula 1 cars/sports cars have a spoiler designed to use this effect to push the car down to stay on the track.
14. 14. BERNOULLI EFFECT • ONLY TALK ABOUT THE BERNOULLI EFFECT IF THE OBJECT IS NOT ROUND e.g. a discus, a javelin, a rugby ball
15. 15. Magnus Effect – types of spin Top Spin View from side Ball Dips Decreases distances travelled Slice View from top Ball deviates right Back Spin View from side Ball floats Increases distances travelled Hook View from top Ball deviates left
16. 16. Magnus effect Slower moving air creates high pressure above the ball Pressure Direction of spin Direction of travel always moves from high to low – this causes the ball to dip as it travels Faster moving air creates low pressure underneath the ball
17. 17. Top Spin Magnus effect Direction of travel Direction of spin The top of the ball: • The surface of the ball is travelling in the opposite direction to the airflow • Causes air to slow down and causes high pressure The bottom of the ball: • The surface of the ball is travelling in the same direction as the air flow • Causes air to speed up and causes low pressure Consequence: • Pressure difference causes ball to deviate towards the area of low pressure. • In the case of top spin, the ball dips and the distance travelled is decreased from the non-spinning flight path
18. 18. Spin and Bounce – Friction important aspect! Top Spin • Bottom surface of ball wants to slide backwards when contact is made with ground • Friction will oppose this motion and act in a forward direction • This causes ball to skim off surface quickly at a low angle • E.g. Tennis – players like top spin as result is ball increases in speed as bounces allowing a shorter time for the opposition to hit the ball
19. 19. Back Spin • As the ball hits the ground it wants to slide forwards • Friction will oppose this motion and act backwards • This causes the ball to kick up from the surface at a large angle to the floor • E.g. some table tennis players can get so much back spin on the ball, when the ball lands it bounces back over the net • E.g. Basketball – back spin essential to successful shots. Will help sink the shot after rebounding off back board. (Think Technique of „flicking the wrist when releasing the ball to gain back spin) • E.g. Golf – back spin helps ball float to a further distance and control the landing
20. 20. Back Spin – Perfect Basketball shot “Using a computer simulation of millions of trajectories based on shots by the best free-throw shooters, Silverberg and colleague Chau Tran determined how various factors affect the chance of success. The magic formula: • a launch angle of 52 degrees, • three revolutions per second of backspin, • and aiming for a spot 7 centimeters (2.8 inches) back from the center of the basket, toward the back of the rim.”
21. 21. Learning Outcomes Be able to: • Name 3 things that effect how far a projectile travels horizontally • Explain what effects the optimal angle of release • Explain what a parabola flight path is and what causes deviations from parabola flight path. • Apply the Bernoulli Principle to a sporting situation • Explain the Magnus effect with relation to the spin placed on an object in flight.