Biomechanics Basic Principles

Question 1

scalar quantity characteristics

Answer 1

have magnitude only (no direction)
can be positive or negative
add algebraically
can only add quantities of the same units

Question 2

vector quantity characteristics

Answer 2

have magnitude and direction

usually noted by bold type of arrow or underline

Question 3

scalar or vector:

• displacement
• force
• speed
• velocity
• acceleration
• length

Answer 3

displacement: vector
force: vector
speed: scalar
velocity: vector
acceleration: vector
length: scalar

Question 4

center of mass
-what is it
center of gravity
what is it

Answer 4

center of mass
-point at which the entire mass of an object can be considered to be located
center of gravity
-balance point for the objectt

Question 5

relationship between stability, COM and base of support

• how do you increase?
• how do you decrease

Answer 5

increased base of support results in increased stability

Question 6

what parameters do we need to know about body segments?

Answer 6

mass of each segment

location of the COM for each segment

Question 7

where is the COM of the whole body?

Answer 7

S2

Question 8

Newtons First Law

• name
• what does it say?
• what is static equilibrium?

Answer 8

Law of Inertia
-an object at rest will stay at rest, unless it is acted on by an unbalanced external force
-an object in motion will stay in motion, unless it is acted on by an unbalanced external force
static equilibrium
-state in which the sum of the forces and moments acting on a system equal 0
-the system is not in motion

Question 9

Newton’s second law

• name
• what does it say?

Answer 9

Law of Acceleration
-acceleration is produced when a forces acts on a mass (sum of forces = ma)
-acceleration = force/mass
a larger mass requires a larger force to accelerate (or decelerate)

Question 10

Newton’s Third Law

• name
• what does it say?

Answer 10

Law of Reaction

• for every action there is an equal and opposite reaction
• reaction force acts in the opposite direction, along the same line of action as the action force

Question 11

Translational Motion Determining Resultant Forces

-3 cases of forces acting at one location

Answer 11

Collinear Force System
Concurrent Force System
Pulley Force System

Question 12

Collinear Force System

• description (3)
• example

Answer 12

forces act on the same segment
forces are coplanar (act in the same plane)
forces are collinear (act along the same line)
example
-tug of war

Question 13

concurrent force system

• description (3)
• example

Answer 13

forces act on a single segment
forces are coplanar
lines of action are at angle to each other
example
-quads and VMO pulling on tibia

Question 14

pulley force system

• purpose
• how does it do this?
• anatomical examples

Answer 14

purpose
-produce greater moment with less force
how
-increase mechanical advantage of increasing moment arm
anatomical pulleys
-patella
-middle deltoid

Question 15

rotational motion terminology

• torque =
• moment =
• moment arm =
• moments have…
• CCW vs. CW

Answer 15

torque = moment = moment of force
moment = force * distance
moment arm
-perpendicular distance from the axis of rotation (fulcrum) to the line of action of the force
moments have magnitude and direction (vector)
CCW = +ve; CW = -ve

Question 16

Right hand rule

Answer 16

I have no idea

Question 17

force couples

-characteristic requirements (4)

Answer 17

Parallel forces
equal magnitude
opposite direction
separated by a distance

Question 18

first class levers

• where are forces?
• relative length of moment arm
• example

Answer 18

external force (load, gravity) and internal force (muscle) on opposite sides of fulcrum
relative length of moment arms can vary (MAmuscle can be ,= MAexternal)
example
-see-saw

Question 19

second class levers

• where are the forces?
• moment arm lengths
• purpose
• example

Answer 19

fulcrum and internal force (muscle) on opposite sides of external force (load, gravity)
MAmuscle always > MAexternal
great mechanical advantage - can lift very heavy loads, but only through short distances
-wheelbarrow

Question 20

third class levers

• where are the forces?
• moment arm lengths
• purpose
• example

Answer 20

fulcrum and external force (load, gravity) on opposite sides of internal force (muscle)
MAexternal always > MAmuscle
purpose
-small shortening of muscle causes large movement of the segment, poor mechanical advantage
very common in body
example
-biceps