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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
Newton's Third Law at heel contact
- The force generated by heel strike is applied to the ground - The ground is pushing back of on the heel (ground reactive force)
26
Work
- Work is force x displacement - W = F x d - Measured in joules
27
Work results when
- A force causes displacement - Mechanical Work - Physiological Work - No displacement means no work
28
Work applied to heel strike
- There is no displacement of the stance limb, therefore no mechanical work - But there is physiological work
29
Power
- The rate at which work is done upon an object - P = W/t - Measured in watts
30
Watt
- Work = joules - Time = seconds - Joules/second = Watt
31
Efficiency
- A comparison of the energy output to the energy input - Percent efficiency = (energy output/energy input) x 100% - Symbol n
32
Torque
- 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
Torque relates to
- The axis of rotation that drives the rotation | - Measured in Newton-meters
34
Moment
- 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
Energy
- The ability to perform work - W = F x d - Units are joules
36
Two primary forms of energy associated with movement
- Potential Energy | - Kinetic Energy
37
Potential energy
- 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
Kinetic energy
- Energy possessed due to the motion of an object | - KE = (1/2)mv^2
39
Kinetic energy requirements
- An objection must be moving | - Its energy is dependent upon its mass and velocity
40
Law of conservation of energy (first law of thermodynamics)
- 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
In trauma the degree of injury is related to
- The energy of the injuring element | - The interaction between that element and the victim
42
Linear versus angular terms
- 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
Translation
- Forward linear movement | - Requires rotation for walking
44
Rotation
- Movement occurs through our joints and about the joint axes - Movement around a fixed axis - No forward movement
45
Walking combines
- Translation | - Rotation
46
Archimedes Law of the Lever assumption 1
- 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
Archimedes Law of the Lever assumption 2
- When two weights balance if something is added to one, they no longer balance - The side with the increased weight goes down
48
Archimedes Law of the Lever assumption 3
- If two weights balance and something is taken away from one, they no longer balance - The unchanged side goes down
49
First class levers
- Skull | - Ankle joint
50
The skull as a first class lever
- Head nods forward and backwards | - Head nods side to side
51
The ankle joint as a first class lever
- Open kinetic chain - The lever is suspended (no axial load) - Axis is the ankle joint
52
Ankle joint lever components in open kinetic chain
- Plantarfelxion = effort of tendo Achilles posterior to ankle joint - Dorsiflexion = effort of anterior muscle group - Foot accepts the load
53
Second class lever
- The load exists between the fulcrum and the effort | - Force is applied in an opposite direction from load
54
Equal load and force on second class lever
- MA = 1
55
If effort provides greater force than load on a second class lever
- MA: Load force x distance ÷ effort force x distance = <1 | - Object will move towards the direction of effort
56
If the load force is greater than effort on a second class lever
- MA: Load force x distance ÷ effort force x distance = >1 | - Object will move away from the direction of effort
57
The ankle joint as a second class lever in closed kinetic chain motion
- Weight bearing (there is an axial load) - Fulcrum (axis): ankle joint - Effort: tendo Achilles - Load: the body and any weight it carries
58
Third class lever
- The effort is between the fulcrum and the load
59
In a third class lever, the object will move in the direction of the load if
- MA > 1 | - Load force x distance from fulcrum ÷ effort force x distance = >1
60
In a third class lever, the object will move in the direction of effort if
- MA < 1 | - Load force x distance from fulcrum ÷ effort force x distance from fulcrum
61
Third class lever components example
- Fulcrum (joint axis): elbow - Effort: contraction of the biceps brachii - Load: what is held within the hand
62
Extension of knee joint
- Class 3 lever is operating | - Effort is between the axis (fulcrum) and the load (lower leg)
63
First and second class lever efficiency
- Generally efficient | - The closer the load to the fulcrum, the more efficient
64
Third class lever efficiency
- Least efficient | - Make up the majority of body levers
65
Benefit of efficiency
- Get the maximum work from the least amount of effort
66
Mechanical advantage
- Measures the amplitude of force | - If is a ratio between the load and the force applied by the effort
67
Movement in the direction of effort requires:
- Force of the load x distance from fulcrum must be less than force of muscular effort x distance from fulcrum - MA < 1
68
Movement in the direction of load requires
- Force of the load x distance from the fulcrum must be greater than force of muscular effort x distance from fulcrum - MA > 1
69
Equilibrium
- No movement | - MA = 1
70
If load and effort are equal forces (regarding mechanical advantage)
- Effort distance twice as far from fulcrum compared to load | - Effort has “twice” the leverage or mechanical advantage
71
Mechanical advantage (MA) equation
- MA = (Force B/Force A) | - MA = (Load/Effort)
72
If the effort and load forces are equal (regarding mechanical advantage)
- Load is three times the distance from the fulcrum - Load is three times greater than effort - Load has the mechanical advantage
73
Pulley system
- Change the effective direction of the applied force - Transmit force - Gain mechanical advantage by changing the angle of pull for the muscle
74
The knee as a pulley system (extension) is an interaction between
- Patella - Quadriceps - Patellar tendon
75
Role of the gracilis muscle in the knee as a pulley system
- Course along condyles | - Increase the angle of pull which minimizes force required
76
The ankle as a pulley system
- Peroneus longus changes direction
77
Role of the peroneus longus in the ankle as a pulley system
- Posterior to fibular malleolus: assists with plantarflexion - Cuboidal notch: everts foot and plantarflexes first ray

Intro to Biomechanics (8 decks)

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