Test Three system as a machine Flashcards
machine
an apparatus/system that uses the combined action of several parts in order to apply mechanical force
what part of the body can technically be classified as an intrinsic machine
joint
what the three types of machines in the human body
lever systems, wheel and axis systems, pulley systems
machines function
transmit a force, increase the magnitude of a force, increase the linear distance and velocity of a force, change the direction of a force
example of transmit force
tendons transmit muscle forces to bones
example of increase the magnitude of a force
less effort required to move a given resistance
example of increase the linear distance and velocity of a force
a resistance is moved a greater distance or at a faster rate than the motive force
example of change the direction of a force
a resistance is moved in a different direction that that of the motive force
lever system
consists of a rigid or semi-rigid object (lever) that is capable of rotating about an axis (fulcrum)
purpose of lever system
to transmit energy from one place to another
what is needed to produce the torque necessary to rotate the lever
fulcrum placed on axis of rotation, force must be off-axis
what are the two types of torque in a lever system
motive torque and resistive torque
what is a motive torque
an eccentrically applied force that attempts to rotate the lever in one direction about the fulcrum
what is a resistive torque
an eccentrically applied force that attempts to rotate the lever in the opposite direction
what are the parts needed to form a lever system
rigid lever, fulcrum, motive torque and resistive torque
example of rigid lever
bones
example of fulcrum
joints
example of motive torque
muscles
example of resistive torque
weight of segment
mechanical advantage
the relationship of the motive force to a given resistive force
example of mechanical advantage
the amount of one required to overcome the other
what causes variation with the system of mechanical advantage
based on the location of the fulcrum
as fulcrum placement changes, the relative lengths of the
moment arms for the motive and resistive forces varies
if fulcrum is in middle what happens with resistive or motive force
they dont have an advantage due to the moment arms are the same length
if the fulcrum is moved farther away from the motive force
then its moment arm becomes longer and gains a mechanical advantage, gain in force production
if the fulcrum is closer to the motive force
then the moment arm for the resistive force becomes longer, and the resistive force has the advantage, gain in linear distance and velocity
three types of lever systems
first, second and third
first class lever
one in which the fulcrum is between the motive and resistive force, balance two forces
which lever system is the most versatile
first class
how can the first class lever be capable of creating an advantage in force
the fulcrum can be moved farther from the applied motive fore
since the resistive end travels a greater linear distance in the same time of the first class lever, the resistive end of the lever also has
a greater linear velocity
the first class lever system is being used
to gain an advantage in linear range of motion and velocity
final function of a machine is to
change the effective direction of an applied force
second class lever system
the resistive force is between the fulcrum and motive force
what are the implications of the second class lever
the moment arm for the motive force will always be greater than the moment arm of the resistive force
levers of the second class are always used
to gain an advantage in force production
short moment arm for resistive force in second class
linear distance traveled is small relative to motive end, no advantage in linear range of motion and velocity gained
second lever, resistance is moved in the
same direction as the applied force, cant be used to change the effective direction of the applied force, or balance two forces
third class lever
the motive force is between fulcrum and resistive force
implications of third class lever
the moment arm for the motive force will always be less than the moment arm of the resistive force
third class levers are used for
to gain advantage in linear range of motion and velocity
third class lever has short moment arm for motive force so
a dispropotionately large motive force must be produced in order to overcome the resistive force
the human musculoskeletal system is designed for increased
linear range of motion and velocity
many musculoskeletal arrangements in the human body can be classified as
third class lever systems
pulley system
consists of an object that acts as a wheel around which a flexible cord is pulled
major functions of pulley systems
change the effective direction of the applied force, transmit forces, gain an advantage in force by changing the angle of pull for the muscle
angle of pull
the angle at which the muscle force acts relative to a given axis or lever.
wheel and axle system
consists of an object acting as a wheel that is secured to a smaller wheel, called the axle
when either the wheel or axle rotates
the other part of the system rotates
function of wheel and axel system
transmit a force, gain an advantage in force or linear range of motion and velocity
wheel and axle system is actually a lever with
a tangential force applied to a moment arm that is equal to the radius of the wheel or axle
motive force is applied where in wheel and axel system
outside of the wheel
the force is eccentric in wheel and axel, what is produced
torque
the large the wheel, the more
off-axis the force is applied
a large wheel provides a
large moment arm for the applied force
compared to the wheel, the axels radius is
small
if force is applied to axel then
torque production is compromised
motive force must be applied where to wheel and axle
wheel which provides advantage in force
in wheel and axle, to gain an advantage in linear range of motion and velocity
apply the motive force to the axle
example of wheel and axle in the musculoskeletal
skull and torso rotating with the spine, skull and torse wheel that rotate around axle spine
what is static equilibrium
a situation in which the system is in linear and rotation equilibrium and possesses zero linear or rotational velocity
what is dynamic equilibrium
system in motion, but is experiencing no change in velocity or direction
linear stability
resistance of a body to having its linear equilibrium disrupted
rotational stability
the resistance of a body to having its rotational or angular equilibrium disrupted
ways to increase rotational stability
keep the center of gravity in the middle of the base of support, lower the center of gravity of object, move the center of gravity to one side of the base of the support, as long as its the same side of the base on which the external force will be applied
