Chapter 3

Question 1

internal vs external forces

Answer 1

• int: exerted within a system that can change position of CG WITHIN system
• ext: exerted on a system cause displacement of CG of system within env’t

Question 2

steps that drive motion

Answer 2

• internal forces change shape within body
• make external contact w/ env’t
• external force changes CM on body

Question 3

what moderates muscle force production

5 of them

Answer 3

• # and size of muscle fibers
• fiber type recruitment
• type of contraction
• force length velocity relationship
• neuromuscular properties

Question 4

steps to model muscle force

Answer 4

• identify FBD (line from axis to insertion point
• identify muscle force vector (arrow from pnt of application in direction muscle pulls
• position LRS

Question 5

how do you position a LRS to model muscle force

Answer 5

• origin on pt of application
• x axis parallel to moving seg (FBD)
• positive x axis on side of origin w/ jnt
• positive y axis on side of origin w/ muscle

Question 6

what is the SC and RC

Answer 6

SC: x axis or horizontal comp
RC: y axis or vertical comp

Question 7

what is the SC force acting at jnt

Answer 7

+ SC = compressive

- SC = dislocation

Question 8

what angles do not have a dominant force

Answer 8

45 and 135

Question 9

what angles are the best movers/best stabilizers

Answer 9

• mover: closest to 90

- stabil: closest to 0