Forces, Moments, Equilibrium

Question 1

Force

Answer 1

Mechanical disturbance or load

caused by one object acting on another object

Question 2

4 components of a force

Answer 2

Magnitude,
Line of action,
Direction,
Point of application

Question 3

Types of forces affecting the foot

Answer 3

External (acting on foot),

Internal (acting within the foot)

Question 4

Largest external force acting on foot under regular circumstances

Answer 4

Ground reaction force (GRF) AKA vertical ground reaction force (VGRF)

Question 5

Ground reaction force (GRF)

Answer 5

Ground pushing up on plantar aspect of foot

Question 6

Newton’s 3rd law of motion

Answer 6

For every action, there is an equal and opposite reaction

Question 7

Newton’s 2nd law of motion

Answer 7

F = ma

The heavier the object, the greater the force required to move the object.

Question 8

Newton’s 1st law of motion

Answer 8

Inertia: an object at rest (or in motion) stays at rest (or in motion) until acted on by a force

Question 9

General measurement of GRF vs internal forces within foot

Answer 9

GRF = magnitude and 3D location via force plate

Internal F = estimation (device implant will alter the F being measured)

Question 10

Force vs Torque

Answer 10

Force = linear vector quantity (F)

Torque = rotational moment or moment of force (M), force acting across an axis of rotation

Question 11

Importance of joint moments in every day activity

Answer 11

Rotational forces producing joint movement (walking) and stability (standing)

Question 12

Do podiatrists, chiropodists, and pedorthists need to understand joint moments?

Answer 12

Yes

crucial for understanding biomechanics of foot motion and stability

Question 13

Rotational equilibrium

Answer 13

Moments acting in one direction across an axis of rotation are counterbalanced by moments acting in the opposite direction across the same axis

Question 14

Net acceleration / angular velocity during rotational equilibrium

Answer 14

Net acceleration = 0 and/or constant angular velocity

Question 15

Is constant angular velocity always = 0 for rotational equilibrium

Answer 15

No.

Joint stable = 0 degrees/second
Joint moving at constant angular velocity of 5 degrees/second can also be in rotational equilibrium because net acceleration = 0

Question 16

Stable joint in terms of biomechanics

Answer 16

Joint is in a state of rotational equilibrium due to equal moments about the joint axis.

Question 17

Moving joint in terms of biomechanics

Answer 17

Joint acceleration occurring due to unequal moments about the joint axis.

Question 18

F Magnitude

Answer 18

Quantity or amount of F

Question 19

F line of action

Answer 19

Line along which F acts

Question 20

F direction

Answer 20

direction which F acts

Question 21

F point of application

Answer 21

Point on object where F is acting

Question 22

Mechanics

Answer 22

Branch of physics concerned with motion and deformation of bodies acted on by mechanical disturbances (forces)

Question 23

Biomechanics

Answer 23

Examining forces acting on and within a biological structure and effects produced by the forces

Question 24

Podiatric biomechanics

Answer 24

Biomechanics of the foot and lower extremity

Question 25

Moment arm

Answer 25

d = perpendicular distance from line of action of F to axis of rotation

Question 26

Lever

Answer 26

a rigid rod that moves on a fixed point or fulcrum when a force is applied to it e.g. a bone (rod) moving on a fixed point (joint)

Question 27

Effort

Answer 27

in a lever system, the force applied to move a load e.g. muscle contraction provides the effort by pulling on the insertion point of the muscle to the bone

Question 28

Advantage of a lever

Answer 28

mechanical advantage | less effort to move a heavier load or move a load further/faster

Question 29

Category of lever determined by 3 factors

Answer 29

relationship of the: | fulcrum, load, and effort

Question 30

1st Class Lever

Answer 30

effort is at one end of lever load is at the other end of lever fulcrum is between e.g. Scissors, seesaws, lifting your head from your chest

Question 31

2nd Class Lever

Answer 31

effort is at one end of lever fulcrum is at other end load is between them e.g. Wheelbarrow, standing on your toes

Question 32

3rd Class Lever

Answer 32

load is at one end of lever fulcrum is at other end of lever effort is between them e.g. most skeletal muscle actions in the body; muscle can attach close to the joint which means effort generated with little shortening of the muscle

Question 33

Changes in positioning of effort, fulcrum, and load modify what 3 aspects of muscle activity

Answer 33

speed of contraction range of movement weight of the load that can be lifted

Question 34

lever class characterized by rapid movement and large range of motion

Answer 34

3rd class lever

Question 35

lever class characterized by great strength at the expense of speed and range of motion

Answer 35

2nd class lever

Question 36

speed levers

Answer 36

lever systems that operate at a mechanical disadvantage force is lost but SPEED and range of movement are gained

Question 37

power levers

Answer 37

systems that operate at a mechanical advantage great STRENGTH and more stable, but slower