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3 summation of forces


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  • 1. Summation of Forces
  • 2. Forces produce movement and a force is simply a pull or a push. We cannot see force, but are aware of it because of the effects it produces.
    Biomechanics is the science concerned with understanding the internal and external forces acting on a human body and the effects produced by these forces. Internal forces are those forces created inside the athlete's body by the action of muscles pulling on bones. External forces are those acting outside the body such as gravity and friction.
    • IAAF “Introduction to Coaching Theory”
    Summation of Forces
  • 3. When several joints are used in a skill, their sequence and timing are important. This principle tells us when the joints should be used. Movement should begin with the big muscle groups and move out through the progressively smaller muscles, from big to small. This pattern produces optimal forces and flowing, continuous movement.
        The continuous, flowing movement produces a summation of forces, forces adding together. The force generated by one part of the body is built on by the force of subsequent joints. In the well timed shot put, the hip action commences just as the leg extension decelerates. The shoulder action commences as the hip rotation decelerates and so on.
        The release velocity of an implement depends on the speed of the last part of the body at release. The correct sequence and timing allow the athlete to attain maximal release velocity.
    Summation of Forces
  • 4. Summation of forces
  • 5. Compared to land based human motion, aquatic locomotion differs in the following ways,
    Buoyancy is the primary force versus gravity
    The substance (water medium) gives when pushed against
    Water resistance is greater than air resistance, and
    Horizontal (swimming)  and vertical positions (shallow water exercise, deep water running) are assumed in the water.
    Aquatic Locomotion
  • 6. Since water is 800 times more dense than air, the energy expenditure to move at a given velocity is great.  Water resistance encountered in swimming consists of
    Form drag,.. this is the greatest resistance encountered by the swimmer and is due to body frontal surface area exposed to the water
    Surface drag (skin friction),.. caused by the water coming in contact with the skin; swimmers do shave their bodies in order to reduce surface drag,..  and, 
    Wave drag,.. the body moving partially in water and in air creates waves which tend to offer resistance to the swimmer.  The amount of resistance the swimmer encounters depends on velocity of movement and type of movement being performed in the water (for example, freestyle swimming versus breaststroke swimming).
    Aquatic Locomotion
  • 7. Basic mechanical principles as applied to swimming involve the following:
    The initial mechanical challenge  is changing inertia.
    Velocity of swimming is directly related to stroke length and stroke rate.
    Propulsive force in the water should be applied so that linear body velocity fluctuations are minimized.
    The body will move in the opposite direction from that in which the propulsive force is applied.
    Both lift and drag forces  result in forward progression of the swimmer.
    Aquatic Locomotion
  • 8. 6.  The more streamlined the body, the less external resistance to movement. 7.  The resistance or drag on a body in any fluid increases approximately with the square of the velocity. 8.  Movement of any body part in the water results in movement of the rest of the body in the opposite direction (i.e., lifting the head results in the feet dropping,.. therefore more body surface area is exposed to the water, which results in poor efficiency. 9.  Minimizing drag and enhancing metabolic power delivery (energy output) will result in improved swimming performance
    Aquatic Locomotion
  • 9. Think: about how learning about forces can assist with skill acquisition
    Pair: find a partner and discuss your thoughts
    Share: one partner from each pair will present your discussion to the class
    Did we all come to the same conclusions?
    Think, Pair, Share
  • 10. Research Report
    800 Words
    Biomechanical Analysis of videotaped freestyle swimming stroke performance
    (refer to assessment task booklet and rubric)
    Assessment Task
  • 11. Theory: Types of Motion
    Prac: Freestyle 25m sprint video recording
    Looking Forward to Next Lesson: