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# biomechanics final*

### chapters 10-14

Question | Answer |
---|---|

statics | covers situations in which all forces acting on the body are balanced (in equilibrium) |

dynamics | branch of biomechanics, dealing with bodies subject to unbalance |

kinematics | branch of mechanics that considers the forces that produce or change motion |

scalar quantities | single quantities (size or amount |

vector quantities | double quantities (magnitude and direction) |

relative motion- | the act or process of changing place or position with respect to some reference object |

translatory motion | object is translated as a whole from one location to another |

rectilinear motion- | the straight-line progression of an object as a whole with all its parts moving the same distance in the same direction at a uniform rate of speed |

curvilinear motion- | refers to all curved translatory movement (moves in curved pathway) |

angular/rotary motion- | when an object acting as a radius moves about a fixed point. |

reciprocating motion | denotes repetitive motion |

external factors modifying motion- | friction, air resistance, water resistance |

internal/ anatomical factors modifying motion- | friction in joints, tension of antagonists. ligaments and fascia, anomalies of bone and joint structure, atmospheric pressure inside joints, presence of interfering soft tissues |

speed equation= | distance/ time |

velocity equation= | displacement/time |

mean acceleration= | final velocity- initial velocity/ time |

a= | v/t |

v= | at |

t= | v/a |

factors that control the range of a projectile: | speed of release, angle of projection, and height of release |

angular displacement equation= | C=2(pi)r |

force- | that which pushes or pulls through direct mechanical contact or through the force of gravity to alter the motion of an object |

what kind of quantity is force? | vector! |

force possess both... | magnitude and direction! |

internal forces- | muscle forces that act on various structures of the body |

external forces- | outside the body (weight, gravity, air or water resistance, friction) |

magnitude is directly affected by what? | muscle fibers |

point of aplication | point at which force is applied to object |

anatomical pulley- patella- | the patella increases angle of pull and increases rotary component |

law of inertia- | body continues in its state of rest of uniform motion unless an unbalanced force acts upon it |

law of acceleration- | F=mass x acceleration, acceleration is directly proportional to force causing it and inversely proportional to mass of object |

impulse- | Ft= m(v-u) product of force and time is applied |

momentum= | mass x velocity |

What are linear forces? give an example. | forces applied in same direction along the same action line ex) gastrocs and soleus acting at ankle joint, psoas and iliacus acting at hip joint |

What are concurrent forces? give an example. | forces acting at the same point of application but at different angles. ex) several fball players blocking each other in blocking situation |

What are parallel forces? give example. | forces are not in the same line but parallel to each other act at different points on body ex) holding a 10 N weight in hand with arm flexed at 90 degrees |

conservation of momentum- | in any system where forces act on each other, the momentum is constant |

What are the 6 forces that modify motion?? | 1) gravity 2) reaction forces 3) weight 4) friction 5) elasticity and rebound 6) fluid forces |

what is friction? | the force that opposes efforts to slide or roll one body over another |

friction is proportional to? | the force pressing two surfaces together |

what is elasticity? | the ability of an object to resist distorting influences and to return to its original size and shape when the distorting forces are removed. |

coefficient of elasticity- | e= the square root of bounce height/ drop height |

The size of the rebound angle compared with that of the striking angle depends on | the elasticity of the striking object and the friction between the two surfaces |

a ball coming in with backspin hitting the floor has a | smaller angle of reflection |

balls thrown with topspin will rebound from horizontal surfaces lower and with more horizontal velocity than that with which they struck the surface | true |

balls hitting a horizontal surface with backspin rebound at | higher bounce and are slower |

a ball with no spin will.. | develop some top spin on the rebound |

a ball hitting with topspin will... | develop greater topspin when rebounding |

laminar flow | if fluid around an object is smooth and unbroken |

drag force | result of pressure on the leading edge of the object and the amount of backward pull produced by turbulence on trailing edge |

Bernoulli's principle- | the pressure in a moving fluid decreases as the speed increases |

eccentric force- | a force whose direction is not in line with the center of gravity of a freely moving object or the center of rotation of an object with a fixed axis of rotation |

torque- | the turning effect of an eccentric force, or moment of force |

torque equation= | torque = force x moment arm (t=f x d) |

moment arm- | the perpendicular distance between the force vector and the axis |

force couple- | effect of equal parallel forces acting in opposite directions |

principles of torques- | resultant torques of a force system must be equal to the sum of the torques of the individual forces of the system about the same point. |

What is a lever? | a simple machine that operates according to the principle of torques; a rigid bar that can rotate about a fixed point when force applied to overcome resistance |

fulcrum- | fixed point about which a lever turns when force applied |

effort arm (EA)- | the perpendicular distance between the fulcrum and line of force of the effort |

resistance arm (RA)- | the perpendicular distance between the fulcrum and the line of resistance force |

first class levers- | axis lies between the effort and the resistance |

mechanical advantage of first class levers- | balance |

second class levers- | resistance lies between axis and effort; EA always longer than RA |

advantage of second class levers- | magnifying the effects of effort so takes less force to move resistance |

disadvantage of second class levers- | ROM sacrificed |

third class levers- | effort leis between axis and resistance; Ra always longer of the two moment arms |

principle of levers- | a lever of any class will balance when the product of the effort and the effort arm equals the product of the resistance and the resistance arm. |

1st class lever abbreviation | EAR |

2nd class lever abbreviation | ARE |

3rd class lever abbreviation | AER |

anatomical examples of first class lever- | head on neck, forearm when being extended by triceps against resistance |

anatomical examples of second class lever- | calf muscles |

non-anatomical examples of second class levers | wheel barrow, door handle, nutcracker |

anatomical examples of third class lever | most muscles, biceps |

non-anatomical third class lever- | screen door with spring closing |

principle of levers equation= | E x EA = R x RA |

mechanical advantage- | ability to magnify force |

mechanical advantage (MA)= | resistance/ effort |

MA also = | EA/RA |

moment of inertia equation- | I = sum mr^2 |

angular momentum= | moment of inertia x angular velocity (lw) |

conservation of angular momentum- total angular momentum of a rotating body will remain constant unless | acted upon by external torques |

a decrease in moment of inertia produces.. | an increase in angular velocity |

what is center of gravity? | the balance point or the point about which a body would balance without tendency to rotate |

location of center of gravity of human being in normal standing position varies with: | body build, age, and sex |

females approximate COG (center of gravity)= | at 55% of standing height |

male approx COG= | at 57% standing height |

convert revolutions per second to radians per second | multiply rev/ sec x 360 then divide by 57.3 |

convert radians per second to degrees per second | multiply by 57.3 |