Chapter 4 Flashcards
factors affecting friction
4 of them
- size of normal force holdinf surface together
- type of material of surfaces in contact
- smoothness or irregularities of the surfaces
- velocity of movement
how to model friction
- origin on COP
- x axis aligned parallel to surfaces in contact
- pos x axis in direction of impending motion
- pos y axis 90 degrees counter clockwise from pos x axis
how can the co efficient of frcition be exressed?
- ratio of frictional force to normal force
- % of normal force required to slide object
what does it mean when co efficient of frirction is 0 and 1
- 0: frictionless surface
- 1: frictional force is equal to normal force
describe static friction
force of friction that resists onset of motion
- COF=1
- greater than sliding friction
describe kinetic friciton
- force of friciton that resists motion
- 1 > COF > .1
what is antero-posterior force
- comp along y axis
- acts as propulsive or breaking force
example of how AP force works
during walking:
- during heel strike: posterior (or negative) force prevents foot from moving anteriorly and acts as breaking force
- during toe-off: anterior (or positive) force prevents foot from moving posteriorly and acts to propel
what is the medio lateral force
- comp along x axis
- related to energy cost and stability
what is rolling friction?
force of friction that resists rotary motion
COF: < .1
-ocdurs what curved and flat surfaces are slightly deformed during contact and peel away from one another
examples that increase friction
4 of them
- chalk on hands
- gloves used in tennis
- rubber tips on crutches
- mt climber resting on side of mt
examples that decrease friction
5 of them
- sole of bowlers shoe
- chalk in hands
- sharp ice skates
- waxed skis
- ball bearings in roller skates
what happens when an angle of incline increases
- friction decreases
- normal force decreases
