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Intro to Biomechanics > Mechanics > Flashcards

Mechanics Flashcards

1
Q

Kinematics

A
  • Describes the motion

- Position, velocity, acceleration

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2
Q

Kinetics

A
  • Describes how the motion is produced
  • What forces create the motion
  • Types of energy that motion utilizes
  • The power required to initiate and guide the motion
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3
Q

Newton’s laws of motion describe the connection between

A
  • Forces that act upon an object

- The manner in which the object moves

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4
Q

Newton’s First Law (the law of inertia)

A
  • An object at rest stays at rest
  • An object in motion stays in motion with the same speed and the same direction (unless acted upon by an unbalanced force)
  • Predicts behavior of objects when forces are balanced
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5
Q

Two predictions of Newton’s First Law

A
  • Resting objects will continue to rest

- Moving objects will continue to move

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6
Q

Forces applied in Newton’s First Law

A
  • Horizontal and vertical forces are applied to the object
  • These forces act upon the object
  • For motion to occur, inertia must be overcome
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7
Q

Inertia

A
  • Resistance
  • An object has to change its state of motion
  • Solely dependent upon the mass of an object
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8
Q

Newton’s Second Law

A
  • The sum of the net forces acting upon an object equals its mass times acceleration
  • Defines the behavior of objects when forces are not balanced
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9
Q

Newton’s Second Law is the relationship among

A
  • Net force
  • Mass
  • Acceleration
  • Net force is the sum of all forces acting upon an object
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10
Q

Force

A
  • The change in momentum over time

- Occurs when forces are not balanced

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11
Q

Acceleration is dependent upon

A
  • The net force acting upon the object
  • The mass of the object
  • F = m x a
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12
Q

Force definition

A
  • Strength exerted upon an object

- Net force is the sum of all forces exerted on an object

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13
Q

Forces involved with net force calculation

A
  • Gravity

- Resistance forces

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14
Q

Resistance forces

A
  • Inertia
  • Static Friction
  • Dynamic Friction
  • Compression, tensile, and torsional
  • Air resistance
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15
Q

Acceleration

A
  • Proportional to the magnitude of the net force

- Occurs in the same direction of the force applied

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16
Q

Acceleration is inversely proportional to

A
  • Mass applied
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17
Q

Acceleration equation

A
  • Equal to the final velocity minus the initial velocity divided by time
  • (Vf - Vo)/(tf - to)
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18
Q

Acceleration relationships

A
  • Greater mass means greater inertia
  • More force is required to change their motion
  • Increased force = increased acceleration
  • Increased mass = decreased acceleration
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19
Q

Newton’s Third Law

A
  • Whenever one body exerts a force on a second body, the second body exerts
    an oppositely directed force of equal magnitude on the first body
  • “For every action there is an opposite and equal reaction”
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20
Q

Forces do not cancel each other because

A
  • They act upon different systems

- When Body A exerts a force on Body B, then simultaneously, Body B exerts a force on Body A in the opposite direction

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21
Q

Momentum

A
  • mass x velocity
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22
Q

Newton’s First Law (intertia) in walking

A
  • Prior to heel contact, swinging leg has mass and forward momentum
  • At heel strike, forward velocity and momentum go to zero
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23
Q

Newton’s Second Law at heel strike

A
  • The change in momentum is great
  • The time it takes to get to zero
  • The force is very great as heel strike occurs quickly
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24
Q

As we walk faster

A
  • Heel strike is shorter

- Force on the foot is greater (F = m x a, so more acceleration results in greater force)

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25
Q

Newton’s Third Law at heel contact

A
  • The force generated by heel strike is applied to the ground
  • The ground is pushing back of on the heel (ground reactive force)
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26
Q

Work

A
  • Work is force x displacement
  • W = F x d
  • Measured in joules
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27
Q

Work results when

A
  • A force causes displacement
  • Mechanical Work
  • Physiological Work
  • No displacement means no work
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28
Q

Work applied to heel strike

A
  • There is no displacement of the stance limb, therefore no mechanical work
  • But there is physiological work
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29
Q

Power

A
  • The rate at which work is done upon an object
  • P = W/t
  • Measured in watts
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30
Q

Watt

A
  • Work = joules
  • Time = seconds
  • Joules/second = Watt
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31
Q

Efficiency

A
  • A comparison of the energy output to the energy input
  • Percent efficiency = (energy output/energy input) x 100%
  • Symbol n
32
Q

Torque

A
  • Measure of the tendency of a force to rotate about an axis

- The product of a force around a turning point (axis) and the perpendicular distance to that axis

33
Q

Torque relates to

A
  • The axis of rotation that drives the rotation

- Measured in Newton-meters

34
Q

Moment

A
  • The measure of a force’s tendency to cause rotational acceleration about an axis
  • It is calculated as force x distance at right angles
35
Q

Energy

A
  • The ability to perform work
  • W = F x d
  • Units are joules
36
Q

Two primary forms of energy associated with movement

A
  • Potential Energy

- Kinetic Energy

37
Q

Potential energy

A
  • Stored energy
  • It is dependent upon gravity
  • PE = m x g x h
  • Note that g = acceleration of gravity (9.8 m/s^2)
38
Q

Kinetic energy

A
  • Energy possessed due to the motion of an object

- KE = (1/2)mv^2

39
Q

Kinetic energy requirements

A
  • An objection must be moving

- Its energy is dependent upon its mass and velocity

40
Q

Law of conservation of energy (first law of thermodynamics)

A
  • Energy is not created or destroyed
  • Energy can only be converted into other forms
  • In the human body it is converted to heat if not conserved
41
Q

In trauma the degree of injury is related to

A
  • The energy of the injuring element

- The interaction between that element and the victim

42
Q

Linear versus angular terms

A
  • Walking is rotational or angular
  • All joints will rotate about their axis in all three cardinal planes
  • Muscles generate the force to initiate and maintain movement
  • These movements occur against resistance of some sort
43
Q

Translation

A
  • Forward linear movement

- Requires rotation for walking

44
Q

Rotation

A
  • Movement occurs through our joints and about the joint axes
  • Movement around a fixed axis
  • No forward movement
45
Q

Walking combines

A
  • Translation

- Rotation

46
Q

Archimedes Law of the Lever assumption 1

A
  • Equal weights at equal distances balance
  • Equal weights at unequal distances do not balance
  • The greater weight will tilt its end of the lever down
47
Q

Archimedes Law of the Lever assumption 2

A
  • When two weights balance if something is added to one, they no longer balance
  • The side with the increased weight goes down
48
Q

Archimedes Law of the Lever assumption 3

A
  • If two weights balance and something is taken away from one, they no longer balance
  • The unchanged side goes down
49
Q

First class levers

A
  • Skull

- Ankle joint

50
Q

The skull as a first class lever

A
  • Head nods forward and backwards

- Head nods side to side

51
Q

The ankle joint as a first class lever

A
  • Open kinetic chain
  • The lever is suspended (no axial load)
  • Axis is the ankle joint
52
Q

Ankle joint lever components in open kinetic chain

A
  • Plantarfelxion = effort of tendo Achilles posterior to ankle joint
  • Dorsiflexion = effort of anterior muscle group
  • Foot accepts the load
53
Q

Second class lever

A
  • The load exists between the fulcrum and the effort

- Force is applied in an opposite direction from load

54
Q

Equal load and force on second class lever

A
  • MA = 1
55
Q

If effort provides greater force than load on a second class lever

A
  • MA: Load force x distance ÷ effort force x distance = <1

- Object will move towards the direction of effort

56
Q

If the load force is greater than effort on a second class lever

A
  • MA: Load force x distance ÷ effort force x distance = >1

- Object will move away from the direction of effort

57
Q

The ankle joint as a second class lever in closed kinetic chain motion

A
  • Weight bearing (there is an axial load)
  • Fulcrum (axis): ankle joint
  • Effort: tendo Achilles
  • Load: the body and any weight it carries
58
Q

Third class lever

A
  • The effort is between the fulcrum and the load
59
Q

In a third class lever, the object will move in the direction of the load if

A
  • MA > 1

- Load force x distance from fulcrum ÷ effort force x distance = >1

60
Q

In a third class lever, the object will move in the direction of effort if

A
  • MA < 1

- Load force x distance from fulcrum ÷ effort force x distance from fulcrum

61
Q

Third class lever components example

A
  • Fulcrum (joint axis): elbow
  • Effort: contraction of the biceps brachii
  • Load: what is held within the hand
62
Q

Extension of knee joint

A
  • Class 3 lever is operating

- Effort is between the axis (fulcrum) and the load (lower leg)

63
Q

First and second class lever efficiency

A
  • Generally efficient

- The closer the load to the fulcrum, the more efficient

64
Q

Third class lever efficiency

A
  • Least efficient

- Make up the majority of body levers

65
Q

Benefit of efficiency

A
  • Get the maximum work from the least amount of effort
66
Q

Mechanical advantage

A
  • Measures the amplitude of force

- If is a ratio between the load and the force applied by the effort

67
Q

Movement in the direction of effort requires:

A
  • Force of the load x distance from fulcrum must be less than force of muscular effort x distance from fulcrum
  • MA < 1
68
Q

Movement in the direction of load requires

A
  • Force of the load x distance from the fulcrum must be greater than force of muscular effort x distance from fulcrum
  • MA > 1
69
Q

Equilibrium

A
  • No movement

- MA = 1

70
Q

If load and effort are equal forces (regarding mechanical advantage)

A
  • Effort distance twice as far from fulcrum compared to load

- Effort has “twice” the leverage or mechanical advantage

71
Q

Mechanical advantage (MA) equation

A
  • MA = (Force B/Force A)

- MA = (Load/Effort)

72
Q

If the effort and load forces are equal (regarding mechanical advantage)

A
  • Load is three times the distance from the fulcrum
  • Load is three times greater than effort
  • Load has the mechanical advantage
73
Q

Pulley system

A
  • Change the effective direction of the applied force
  • Transmit force
  • Gain mechanical advantage by changing the angle of pull for the muscle
74
Q

The knee as a pulley system (extension) is an interaction between

A
  • Patella
  • Quadriceps
  • Patellar tendon
75
Q

Role of the gracilis muscle in the knee as a pulley system

A
  • Course along condyles

- Increase the angle of pull which minimizes force required

76
Q

The ankle as a pulley system

A
  • Peroneus longus changes direction
77
Q

Role of the peroneus longus in the ankle as a pulley system

A
  • Posterior to fibular malleolus: assists with plantarflexion
  • Cuboidal notch: everts foot and plantarflexes first ray

Intro to Biomechanics (8 decks)

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