Biomechanics Definitions

Question 1

Kinetics

Answer 1

Study of relation existing forces acting on a body, mass of the body, and motion of the body

Question 2

Kinematics

Answer 2

Describes motion without reference to force

Used to relate displacement, velocity, acceleration, time without reference to cause of the motion

Question 3

Force

Answer 3

Vector quantity which produces or prevents motion

Imposes change of velocity on a material

Question 4

Newton’s 1st Law of Motion

Answer 4

Every object in a state of uniform motion tends to remain in the state of motion unless external forces are applied to it

Question 5

Newton’s 2nd Law of Motion

Answer 5

Relationship between object’s mass (m), acceleration (a), and the applied force (f), is given by the formula F=ma

Question 6

Newton’s 3rd Law of Motion

Answer 6

Every action has an equal and opposite reaction

Question 7

Equilibrium

Answer 7

State of object when no part of object is accelerating

Net force and torque acting on object is zero

Question 8

Inertia

Answer 8

Reluctance of matter to change its state of rest or uniform motion

Fdeltat = mdeltavinitial- mdeltavfinal

Question 9

3 Point pressure system

Answer 9

Principle in orthotic design to achieve joint stability

Provides point of pressure above axis of rotation, point below axis of rotation, and third opposing point at or near the axis of rotation

Question 10

Moment

Answer 10

Measure of turning effect, or torque produced by force acting on a body

Equal to the product of force and perpendicular distance from its line of action to the point at which the body will turn (pivot)

Question 11

Center of gravity and mass

Answer 11

Unique point in object or system which can be used to describe system’s response to external forces and torques

Average position of the system’s mass

Location in an object where mass balances in all planes

Question 12

Force Couples

Answer 12

Moment induced by two equal and opposite forces

Is equal to the moment of one force about the point of action of the other

No resultant force

Question 13

Lever, comprises of 3 components

Answer 13

Fulcrum
- point at which lever rotates

Load
- force applied by the lever system

Effort
- force applied by the user of the lever system

Question 14

1st Class Lever

Answer 14

Fulcrum lies between effort and the load

Question 15

2nd Class Lever

Answer 15

Fulcrum is at one end, effort on the other end, load lies between effort and fulcrum

Question 16

3rd Class Lever

Answer 16

Fulcrum at one end, load at the other end, effort lies between load and fulcrum

Question 17

Friction

Answer 17

Tangential force resisting motion of one surface on another

Question 18

Work

Answer 18

Transfer of energy by force acting to displace a body

Product of force and distance

Question 19

Kinetic Energy

Answer 19

Work done by force along a given displacement

Energy involved in motion

Question 20

Potential Energy

Answer 20

Stored energy due to composition, position, or condition

Question 21

Stability in Standing (2 conditions must be satisfied)

Answer 21

1. Line of action of the TBF must be aligned within the base of support
2. Joints must be stabilized by muscles, ligaments, etc.

Question 22

Base of Support

Answer 22

Region bounded by body parts in contact with some resistive surface that exerts a reaction force against the body’s applied force

Usually feet or devices on the ground

But a hand on a railing or table also qualifies

Larger base of support, greater stability in standing

Question 23

Medial-lateral body shift

Answer 23

Magnitude of GRF on each foot changes as the body shifts from its central position

Only evenly distributed among each foot if TBF is down the middle

Question 24

Line of Action

Answer 24

Straight line extending along the direction of the force through the point of application

In static standing, the line of action of all the forces is purely vertical or in the y direction only

Question 25

External Moment

Answer 25

Moment caused by a force outside the body in question

Question 26

Active Internal Moment

Answer 26

Moments intentionally being created

Metabolic energy is used to create the moment

Muscle Contraction

Question 27

Passive Internal Moment

Answer 27

Moments created without expenditure of metabolic energy

From ligaments, soft tissue, boney block (joint end range)

Moments caused by bracing can also be considered passive internal moments as long as the brace is within the segment being isolated

Question 28

Ankle and Knee Moment most accurately predicted by

Answer 28

GRF

Question 29

Hip Moment most accurately predicted by

Answer 29

TBF

Question 30

Free Body Diagram

Answer 30

Diagram of isolated portion of structure used during free body analysis

For purpose of studying the effect of forces acting on the free body or body segment

Question 31

Link Segment Model

Answer 31

Diagram that uses the line of action of the GRF/TBF to predict the moments that are occurring at a specific body joint

Question 32

Momentum

Answer 32

Produce of mass and velocity

Quantity of motion of a moving body

Vector quantity, has direction and magnitude

Question 33

Weight

Answer 33

Force that is the produce of the pull of gravity on a body’s mass

Always directed vertically downward toward the center of the earth

Earth pulling your body down by gravity is known as the total body force

Question 34

Ground Reaction Force

Answer 34

The force exerted by the ground on a body in contact with it

Equal in magnitude and opposite in direction to the force that the body exerts on the ground