BBiomechanics midterm II Flashcards
what is mechanical work?
product of force and displacement in the direction of that force
means by which energy is transferred from one object to another
why is average force uses for U (mechanical work)
because usually the force applied is not constant
what are the three types of muscle contraction how does this reflect in work?
isometiric (static) = 0 work
concentric. = shortening = postiive work
Eccentric = lengthenign = negative work
What is mechanical energy
the capacity to do work
what is kinetic vs potential energy?
objects capacity to do work due to motion of the object
vs due to position of object
is energy always positive?
yes
do changes in mass or velocity have large effects on KE
velocity (it is squared)
Is Kinetic energy conserved?
No as during impact some KE is converted to other forms like sound and heat
what are the 2 types of potential energy
- gravitataion PE
- Strain energy
What is gravitational PE?
PE due to objects position relatie to earth
What is the case for g in pe?
IT is always positive
what is strain energy?
PE due to the deformation of an objet like bending pole in pole vault, stretched muscle or tendon
what s k in strain energy? what is delta x?
stiffness constant. deformation or change in length
What is the work-energy relationship?
the work done by external forces (other than gravity) acting on an object causes a change in the energy of the object
U= delta E which is Delta KE + Delta PE (we wont incldue strain energy)
How do we maximize kinetic energy (in sports spec)?
large force applied over long distance
What an example of a technique used when doing work to decrease energy?
Flexing lower limb joins to minimize impact - increaing displacement.
How do we do work to decrease energy?
we use techniques and materials to perform negative work on an object to absorb some kinetic energy by increasing displacement of an object to minimize impact force
What is the conservation of mechanical energy?
in the absence of external forces (other than gravity) no work is done and total mechanical energy is constant or conserved
KEi + PEI = (KEf + PEf)
Ei = Ef
In projectiles what happens to KE and PE:
1) before an object is dropped?
2) as it falls?
3) The instant before object strikes ground?
before dropped KE = 0
as it falls PE decreases because height deceasee but KE increases cause it acc due to gravity
Instant before the object strikes the ground it has no PE because h=0
How are PE and KE related in projectiles while falling?
The decrease in PE is equal to the increase in KE
what is power?
The rate of doing work
definition of linear power
product of average force and average velocity
P = U
Δt P = Fd
Δt P = F d
Δt P = Fv
as the velocity of a contraction increases, the maximal force the muscle can generate …
decreases
What decrease w age?
isometric muscle strength