Force

• Two goals of studying sports & exercise biomechanics

  • Enhance skill performance
  • Reduce the risk of injury
• 1 kg mass experiences a 1 m/s^2 acceleration with a force of 1 N (F = ma)
• Kinematics


  Study of description of motion, independent of force
• In Biomechanics, the shape of the object does not change
• Forces come in pairs (action and reaction)
• Basic dimensions

  • Length - meters
  • Time - seconds
  • Motion - speed (m/s), velocity (m/s^2), acceleration (m/s^2)
  • Inertia - resistance to change
  • Mass = amount of matter in the object & it never changes in anywhere in the universe
• Kinetics


  Study of explanation of motion, deals with the forces
• Movement is interaction between two movements
• Forces enable us to walk, run, change directions, stand still
• Forces are exerted by objects on other objects
• Vector

  Size (magnitude) and direction (orientation)
• A force accelerates an object
• Force comes in pairs
• Force


  A push or a pull
• Unit of force is Newton (N): 1 N = 1 kg x 1 m/s^2
• Contact forces

  • Friction force
  • Normal (Contact) forces
  • Gravity (Weight)
• Internal forces

  • Tensile forces
  • Compressive forces
  • Muscle force
  • Muscle lengthening & shortening
• Noncontact forces

  • Gravity, Magnetic forces, Nuclear force
• External forces and internal forces exist
• Weight is a force, and if gravity is the only force acting on an object, it will accelerate at 9.81 m/s^2 (gravitational acceleration)
• Center of Mass (COM) is important in analyzing motion
• If the gravity of the earth is the only force acting on an object, the gravity will accelerate the object
• 9.81 m/s2 is the gravitational acceleration (g)
• In sports & exercise, the only noncontact force is ourselves with the force of gravity
• Mass


  The amount of matter
• Normal Force


  Perpendicular to the surface that an object contacts
• Weight

  Force of gravity acting on an object
• Static Friction vs Kinetic (Dynamic) Friction

  • Static friction force is greater than kinetic friction force
• Contact forces


  Forces that occur between objects in contact with each other
• Friction Force

  Opposes relative motion, proportional to the normal contact force, independent of the size of the surface area, proportional to the roughness of the surface area
• Friction force is independent of the size of the surface area
• Friction force is proportional to the roughness of the surface area
• Friction force is a contact force that acts between and parallel to the two surfaces in contact
• More than one of these external forces will act on us in most situations