chapter 4 Flashcards
work
the product of force applied to a body and the amount of displacement the body undergoes
work letter
U
does work need time
no
work unit
Nm or J
to calculate work we need
force, displacement
concentric
against gravity
eccentric
with gravity
positive mechanical work is done by
force acting on an object if the object displaces in the same direction of the force
concentric
negative mechanical work is done by
force acting on the object when the object displaces in the opposite direction of the force acting on it
eccentric
positive muscle work
a muscle contracts and its point of attachment move in the direction of the muscle pull
concentric contraction
negative muscle work
a muscle contracts and its points of attachment move in the direction opposite the muscle pull
eccentric contraction
does an isometric contraction perform mechanical work
no
energy
the capacity to do work
two types of mechanical energy
kinetic, potential
kinetic vs potential energy
kinetic is motion, potential is stored
two types of potential energy
postion, deformation
an objects capacity to do work because of its
motion
how much KE in a 5oz baseball (145g) thrown at 80mph (35.8m/s)
KE=.5mv^2=92.9J
gravitational PE
energy inherent due to an objects position relative to the earth (vertical energy)
strain PE
energy stored due to an objects deformation
gravitational evergy formula
PE=mgh
calculate strain energy stored in a tendon stretched 5mm if the stiffness (k) of the tendon is 10,000 N/m
SE=.5k (triangle x)^2
.125J
work energy principle:
the net work done by all the external forces acting on an object causes a change in the
mechanical energy of the object
as a moving object rises up in the air
KE ____
PE____
total energy ____
decrease, increase, constant
