LECTURE #13 - torques and moments of force

Question 1

what are the 4 points of force in regards to torque ?

Answer 1

• magnitude
• point of application
• direction
• line of action

Question 2

describe the moment arm :

Answer 2

perpendicular distance between line of action of force and axis of rotation

Question 3

what are the 3 things that internal moment created by a muscle are dependent upon ?

Answer 3

• muscle force (F)
• lever arm (d)
• angle of pull (θ)

Question 4

what does it mean when a muscle produces a co-contraction ?

Answer 4

• creates opposing joint torques (opposite direction)
• motion occurs in direction of net internal moment

Question 5

what is the purpose of antagonist muscle co-contraction ?

Answer 5

control velocity of joint motion and increase stability at joint

Question 6

what type of contraction are the knee extension muscles producing (quadriceps and hamstrings) ?

Answer 6

quadriceps = concentric contraction
hamstrings = eccentric contraction

Question 7

describe the direction concentric is going towards :

Answer 7

the load that is going towards the CLOUDS on the concentric phase (not your body)

Question 8

describe the direction eccentric is going towards :

Answer 8

the load that is going to wads the EARTH in the eccentric phase

Question 9

what are some bad things in regard to muscle co-contraction ?

Answer 9

• co-contraction will lead to deficit
• adding adduction compression (control)
• hamstring more prone to injuries
• functionally bad when creating optimal force

Question 10

what are some good things in regards to muscle co-contraction ?

Answer 10

• adds-stability and control
• increases compressive force

Question 11

what contributes to stuff gait and reduces knee flexion (disease progression) ?

Answer 11

muscle co contraction

Question 12

what is muscle co-contraction ?

Answer 12

the simultaneous activation of muscles on opposite sides of a joint

Question 13

what are some non-muscle contributions (external moment) to joint torque ?

Answer 13

• segment mass will cause a joint moment
• any external object attached or held by segment will produce a joint moment
  ground reaction force

Question 14

what is the internal moment created by a muscle dependent on ?

Answer 14

• force moment arm
• magnitude of co-contraction
• external factors

Question 15

what is equilibrium ?

Answer 15

the state characterized by balance forced and torques

Question 16

what is static equilibrium ?

Answer 16

when a body is completely motionless (at 0)

Question 17

how many conditions of static equilibrium are there ?

Answer 17

3

Question 18

what are the three conditions of static equilibrium ?

Answer 18

• sum of all horizontal forces (or force components) acting on body must be zero
• sum of all vertical forces (or force components) acting on body must be zero
• sim of all torques must be zero

Question 19

ΣF(x) = ?

Answer 19

0

Question 20

ΣF(y) = ?

Answer 20

0

Question 21

ΣT =

Answer 21

0