Force and Motion Relationships

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Force and Motion Relationships

• Concept Module F

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Linear Speed

• How fast a body is moving.
• Speed distance/time

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Linear Velocity

• Velocity is a vector quantity because it
  possesses both magnitude and direction.
• Velocity defines not only the speed at which
  something is moving but the direction in which it
  is traveling as well.
• Vd/t

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Linear Motion

• Describes a systems distance (d) traveled and
  the systems speed and direction (v).
• CG is the reference point for segmental motion.
• During cyclic activities a determined point can
  act as the reference point

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Linear Acceleration/Deceleration

• The speeding up, slowing down or changing
  direction of a system.
• In order for a body/system to experience this
  change, it must be acted upon by some net
  external force.
• The time rate of change in a bodys velocity.
• Achange of velocity/time

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Linear Acceleration/Deceleration Continued

• A v2-v1/t (v2end velocity and v1 is the
  initial velocity)

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g

• Newtons Law of Universal Gravitation
• The force of attraction between two masses is
  directly proportional to the masses of the two
  bodies.
• Example the greater the masses of the two
  bodies, the greater the force of attraction
  between them.
• gacceleration of a body due to gravity and is
  represented as a numerical figure of 9.8 m/sec

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g Continued

• When a body is free of support it is forced
  downward by the gravitational attraction force
  equal to the bodys weight.
• As it falls it will accelerate at a rate of 9.8
  m/sec (during each second it falls)
• If a body is thrown upward, it too will
  decelerate at a rate of 9.8 m/sec (during each
  second it rises)

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Zero Acceleration/Constant Velocity

• If a net external force acts on a system-the
  system will accelerate in the direction of the
  applied force.
• If no net force is acting on a system the linear
  acceleration 0
• If acceleration 0, no change in velocity has
  occurred
• If a body is moving at a given velocity and
  experiences equal opposing forces, there will be
  no change in the systems velocity.
• When velocity is constant zero acceleration

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Zero Acceleration-Continued

• Skydiver Example
• Balloon Example
• Feather Example
• Rare occasions in human motion
• Newtons 1st Law a body at rest will stay at
  rest until a net external force acts to
  accelerate it and a body in motion will stay in
  motion at a constant velocity and in the same
  direction until a net external force acts to
  change it.

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Variable Velocity

• Average velocity The average of velocity
  changes throughout an activity.
• Changes in velocity occur during the course of
  most human experiences due to the type of
  activity, external forces, etc.
• Small time intervals are often the focal point
  for analyzing movement skills. (acceleration
  phases of activity are often most
  scrutinized-propulsion, release, follow-through,
  etc)

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Variable Velocity-Continued

• Instantaneous Velocity Used when analyzing the
  projection of objects also called release
  velocity.
• In projectile situations, as soon as the
  projectile is released at a specific speed and
  direction, its velocity will begin to change due
  to gravity and air resistance. If these forces
  were not present, the projectile would continue
  to travel in a straight line with a constant
  speed.

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Force, Mass and Linear Acceleration Relationship

• Newtons 2nd Law The acceleration of a system
  is directly proportional to the net applied force
  and inversely proportional to the mass of the
  system.
• a F/m or F m x a

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Force, Mass, Acceleration Relationship-Continued

• The greater the force applied to a constant mass,
  the greater the acceleration of the mass.
• As the mass of an object is increased and the
  applied force stays the same, the acceleration of
  the object will decrease.
• As the mass of an object is increased, more force
  must be applied to it to produce a given
  acceleration.

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Acceleration and Deceleration Forces of the Body

• The greater a bodys mass the more friction force
  needed to accelerate/decelerate the mass.
• Runner Example with ground reaction forces.

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Centripetal Force and Radial Acceleration

• Same concept as Linear acceleration.
• The greater the mass being rotated, the greater
  the centripetal force production to cause radial
  acceleration (direction change). Swing example.