lecture 4, exam 1 study guide

Question 1

what is inertia?

Answer 1

directly proportional to its mass –> takes more energy to move a heavier object
tendency to remain unchanged unless acted upon
* Newton’s 1st law

Question 2

what is center of mass?

Answer 2

the point from which its weight force acts
all mass is distributed in all directions
needs to be supported by forces or its unbalanced

Question 3

true or false. there can be COM for the whole body and each segment

Answer 3

true
segment - relatively stable
whole extremity - change when segments change relationship

Question 4

velocity vs acceleration

Answer 4

velocity - how fast you’re moving
acceleration - how fast velocity is moving

Question 5

what is mass moment of inertia?

Answer 5

resistance to a change in body’s change angular velocity

Question 6

is most human motion angular or linear?

Answer 6

angular

Question 7

what does the mass moment of inertia depend on ?

Answer 7

mass of body
distribution of mass about axis of rotation

figure skater - rotates faster when arms and legs are pulled in

Question 8

if a diver has all limbs tucked in while performing a dive, will the mass moment of inertia be increased or decreased? why?

Answer 8

decreased
tucking all limbs increases angular velocity

Question 9

when the COM of a whole extremity is further from hip axis of rotation (leg extended), is the mass moment of inertia increased or decreased?

Answer 9

increased

Question 10

how does impulse and momentum relate?

Answer 10

impulse = momentum change

Question 11

what do free body diagrams help us recognize?

Answer 11

interaction of body and its environment
all forces acting on the system

Question 12

what is the relationship of the X muscle force component (Mx) to the bony segment?

Answer 12

parallel

Question 13

what is the relationship of the Y muscle force component (My) to the bony segment?

Answer 13

perpendicular

Question 14

what does Mx do in a simple hinge joint model?

Answer 14

creates a compression or distraction force between articulating surfaces

Question 15

what does My do in a simple hinge joint model?

Answer 15

creates shear force between articulating surfaces

Question 16

what can Mx cause? what does it not cause?

Answer 16

can cause translation of bone
does not cause torque because the chosen reference system reduces the moment arm to zero

Question 17

what can Y cause?

Answer 17

translation of bone and/or torque of moment arm > 0

Question 18

in elbow flex/ext, Mx creates ______ force when directed _______ elbow

Answer 18

compression ; toward

Question 19

in elbow flx/ext, Mx creates ________ force when directed ______ from elbow

Answer 19

distractive ; away

Question 20

in elbow flx/ext, My with internal moment arm creates flexion _______ at the elbow

Answer 20

torque

Question 21

what are two different ways that the same external torque can be applied against the quad muscle?

Answer 21

1. large resistance and small external moment arm
2. small resistance and large external moment arm

• depends on where you are applying the force (mid shaft tibia vs ankle)