Week 5 (Friction)

What is friction?

• The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other

  • The frictional force acts opposite to the direction of motion or impending motion, parallel to the surface.

What are the types of frictional forces?

• 2 types of frictional forces

  • Fluid Friction: occurs between layers of fluids that are in motion (turbulent and laminar flow in blood)

  • Dry (coloumb) friction - the resistance created by contact forces that develop between dry surfaces

    • Static and kinetic friction

What are frictional forces?

• Friction is present in all human movements

  • Small frictional forces (skating, bobsled)

  • Large frictional forces (judo, football)

• Internal frictional forces

  • Joint articular surfaces

  • Muscle - eccentric contractions

What makes frictional forces, reaction forces?

• Friction only exists in the presence of an applied force with some magnitude that is angential to the surfaces

• Every pair of surfaces has a coefficient of friction (how ‘grippy’ the surfaces are)

  • More grippy surfaces allow for the formation of a larger frictional force

What is the magnitude of frictional forces dependent on?

• The nature of the contacting surfaces (the material)

  • ‘surfaces’ - requires 2 surfaces in contact

• Whether the surfaces are in stationary or in motion

  • Static Friction and Kinetic Friction

• The magnitude of the normal force

  • The normal force is perpendicular to the surface

    • The reaction force from the surface