3.1 newtons laws of motion, force and technology

• Using the laws and principles of physics, enables performer and coaches to:

  • analyse perfomance
  • maximise movement efficiency and sporting technique
  • reduce or prevent injuries
  • design and choose the correct equipment to satisfy the demands of the activity
• Force - a push or pull that alters the state of motion of a body
• Inertia - the resistance of a body to change its state of motion, whether at rest or while moving
• Velocity - the rate of change in displacement
• Momentum - the quantity of motion possessed by a moving body
• Acceleration - the rate of change of velocity
• Newtons 1st Law

  • a body continues in a state of rest or uniform of velocity unless acted upon by an external or unbalanced forces.

  e.g 100m sprinter remains at rest in the blocks until an external force large enough to overcome their inertia creates motion.
• Newtons 2nd Law

  also known as the law of accleration

  • a body rate of change in momentum is proportional to the size of the force applied and acts in the same direction as the force applied

  example - the greater the force applied to the sprinter the greater the rate of change in momentum and therefore acceleration away from the blocks
• Newtons 3rd Law

  • for every action force applied to a body there is an equal and opposite reaction force

  example - 100m sprinter applies a down and backward action force into the blocks, the blocks provide an equal and opposite up and forward reaction force to the sprinter to drive them out of the blocks.
• Internal force - generated by the contraction of the skeletal-muscle
• External force - generated from outside the body and acts upon it

  • weight
  • reaction
  • air resistance
  • friction
• Net force - the sum of all forces acting on a body, also termed resultant force. It is the overall force acting on a body when all individual forces have been considered.
• Balanced - 2 or more forces acting on the body are equal in size and opposite in direction

  net force = 0

  there is no change in motion

  body will remain at rest or in motion with the constant velocity
• Unbalanced force - 2 or more forces acting on a body that are unequal in size and opposite in direction

  net force ≠ 0

  there is a change in motion - acceleration or deceleration
• Weight (N) - gravitational pull that the earth exerts on a body. Acts downwards from the body CoM
• Weight (N) = mass x acceleration due to gravity
• Reaction forces - equal and opposite force exerted by the body in response to the action force places upon it
• Vertical forces:

  • weight
  • reaction
• Horizontal forces:

  • friction
  • air resistance
• Friction (N) - force that opposes the motion of two surfaces in contact
• Air resistance (N) - force opposing motion travelling through air. Form of fluid friction
• Friction is affected by:

  • roughness of ground surface
  • roughness of contact surface
  • temperature
  • size of normal reaction
• Air resistance is affected by:

  • velocity
  • shape
  • frontal cross-sectional area
  • smoothness of surface
• Free body diagrams:

  Vertical - weight (from com extending vertically downwards), reaction force (from the point of contact extending vertically upwards)

  Horizontal - friction (from point of contact usually extending horizontally in the same direction as motion), air resistance (from the CoM and extending horizontally against direction of motion
• Velocity (m/s) = displacement / time
• Momentum (kgm/s)= velocity x mass
• Acceleration (m/s^2) = (final velocity - initial velocity) / time
• Force (N) = mass x acceleration
• Uses of technology:

  • limb kinematics
  • force plate
  • wind tunnels
• Factors affecting air resistance and friction:

  • ground surface
  • contact surface
  • temperature
  • increased reaction force
• Limb kinematics:

  • study of movement in relation to time and space
  • 3D or optical motion analysis
  • joint and limb triangulation
  • computer and software + video/infrared camera capture and convert motion using reflective markers on body landmarks
  • data is immediate, objective and accurate
  • expensive
  • pin pointing axis of rotation can be challenging
• How can limb kinematics be used to enhance performance in sport?

  • injury prevention
  • improve technique
  • prevent joint injuries
  • identify small changes to improve technique
• Force plates:

  • study ground reaction force, assessing the size and direction of forces
  • can predict acceleration rates, work and power output
  • sport biomechanics assessment - e.g gait analysis, balance, rehabilitation and physical therapy
  • rectangular metal plate with built in force transducers - electrical output is proportional to the magnitude of the force applied
  • displayed in 3 planes of motions
  • immediate, accurate and reliable results
  • expensive and specialist equipment
• Wind tunnels:

  • used to develop and optimise aerodynamic efficiency, such as drag
  • object is placed inside the wind tunnel with instruments attached to measure forces produced by air against its surface
  • study the airflow around the surface using smoke or dye in the tunnel
  • aim of wind tunnels is to improve airflow and streamlining - potentially increasing lift and decreasing drag
  • control of variables - increase accuracy and time efficient
  • specialist facilities, expensive and require complex analysis
• roughness of ground surface - increasing roughness friction is increased e.g rubber tracks

  roughness of contact surface - increasing roughness of contact surface friction is increased e.g spikes

  temperature - increasing the temperature of the ground and contact surface friction is increased e.g f1 drivers have a warm up lap

  size of normal reaction - increasing normal reaction friction is increased e.g shot putters have a high mass this creates equal and opposite high reaction force allowing greater friction
• velocity - increase velocity air resistance increases

  shape - aerodynamic shape lowers air resistance known as streamlining

  frontal cross-sectional area - decreasing frontal cross-sectional area air resistance decreases

  smoothness of surface - increase smoothness of surface air resistance decreases