1. NCEA LEVEL 2 Hs
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2. BIOMECHANICS
FORCE SUMMATION
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3. Many skills performed in sport require maximum speed or force to be generated.
Some skills require maximum force to get a result, while others require maximum speed or velocity.
In order to do this, an athlete needs to involve as many body parts as is technically possible.
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4. The movements occur at relatively the same time but in the correct order.
The more body segments involved the greater the force or speed generated.
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5. EXAMPLE
An athlete competing in a discuss competition would generate less force and therefore less horizontal distance, if only the arm and shoulder are used.
Another competitor using force built up from using legs, hips, back, shoulder, arm and wrist in order would throw further.
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6. SUMMATION OF FORCES
Maximum speed is achieved by adding the speed of each segment and transferring this to the final part of the body.
The speed of the last part of the body at the moment of contact or release will determine the velocity of the implement or projectile.
When serving in tennis or hitting a tee shot in golf, at the end of the movement of body segments, the accumulated speed should be transferred to the racquet or club to generate maximum speed or force.
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7. WORKING EXAMPLE OF FORCE SUMMATION
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8. A solution maybe the students awareness of force summation.
The student is unable to produce enough force to propel the basketball to the basket.
A solution maybe the students awareness of force summation.
Eg: When performing the basketball set shot it is important that the body parts move sequentially.
Force summation is the ability to use all body segments involved to generate greater force or speed.
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9. Firstly the basketball player needs a stable base from which to execute their shot.
The knees must flex then move to extension in order to start the movement.
The muscles involved in this actions are the hamstrings and the quadriceps.
The hamstrings initiate flexion followed by the quadriceps being the prime movers for the knee extension.
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10. This movement continues with shoulder extension, elbow flexion and wrist extension. This moves to shoulder flexion, elbow extension and wrist flexion( prime movers included here? )
The end result is a more powerful force that can be transferred to the ball so that it travels as far as it can towards the rim.
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11. FACTORS AFFECTING PROJECTILE MOTION
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12. Any object released into the air is termed a projectile.
The flight path of a projectile consists of a vertical and horizontal component.
What does this mean?
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13. Regardless of the type of object that is being released, or by what means it is being projected, they are all governed by the same principles.
Gravity.
Air resistance.
Speed of release.
Angle of release.
Height of release.
Spin.
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14. GRAVITY
Gravity acts on a body to give it mass. The greater the weight of an object the greater the influence of gravity upon it.
What is the effect of gravity on a projectile?
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15. There are several key factors that bring air resistance into play.
The larger the surface area, the more air resistance will affect the object.
If the surface is rough then air resistance will be greater.
Speed. As speed increases, so does air resistance. (Think of the space shuttle)
Mass. The smaller the mass (lighter the object) the more air resistance will affect it.
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16. Can you give me an example?
Speed of release.
Generally, the greater the speed of release, the greater the distance gained.
In many game situations this is a factor that must be under constant control.
Can you give me an example?
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17. ANGLE OF RELEASE
For any given speed of release, the optimum angle of release is always 45 degrees.
Is this the case in many sports? Why?
What would happen if the angle of release were to high for a given activity?
Poor distance gained
What would happen if the angle of release were too low for a given activity
Poor flight time and possibly poor distance.
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18. Height of release
The inter-relationship between height of release and angle of release is important to consider.
Have you ever noticed that tall basketball players shoot the ball at a lower angle than short players.
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19. The reason behind this can be summarized as follows
As the height of release increases, the angle of release decreases.
As the height of release decreases, the angle of release increases.
THINK ABOUT IT!
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20. SPIN
Consider a game of Tennis. What happens to the distance achieved with a topspin shot compared to one with backspin?
A topspin shot gives poorer distance compared to backspin.
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21. SOOOO……..
This leads us to the following two principles with respect to projectiles and spin.
Range is decreased with topspin.
Range is increased with backspin.
WHY?
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22. Practical Example Question?
How is this biomechanical principle applied to the overhead serve in volleyball. Where can I see this being applied?
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23. ANSWER.
Firstly the speed or the force that the ball is struck/released at is important. The speed at which the ball is struck will determine how far the ball will travel. The striking force must be sufficient enough to allow the ball to cross the net but not enough to mean the ball goes out of play.
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24. The height of release also influences the horizontal distance covered, too high and the ball may go to far, too low and the ball may strike the net. The angle is also important in conjunction with this. The angle and height of release must be judged correctly in order that the serve is successful. Spin can also be applied in order to make the ball dip after the net-making it harder for teams to return.
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25. The weight that needs to be moved.
levers
A lever is used when you want to apply more force.
Most levers have three clearly identified parts:
THE FULCRUM
The pivot point around which the movement happens. In the body this is usually the joint.
2.THE LOAD
The weight that needs to be moved.
3.THE FORCE
The place where the force is applied. In the body this is the effort produced by the muscles contracting .
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26. CLASSES OF LEVER There are three classes of lever.
Not surprisingly they are called:
FIRST CLASS
SECOND CLASS
THIRD CLASS
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27. Third class levers generate speed rather than force.
First class levers can help to either increase force or generate more speed depending on the position of the fulcrum.
Second class levers allow more force to be produced because the effort ,or force arm ,is longer than the resistance arm.
Third class levers generate speed rather than force.
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28. LEVERS IN SPORT
In many sports the equipment you use act as an extension of the levers in your body and helps to generate greater force or sped. Two good examples of levers used in sport can be seen in rowing or golf.
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