Midterm 1 Flashcards
how force is defined
force is the quantity that causes motion or deformation of a body
the units of mechanics are
Mass (kg)
Length (m)
Time (s)
how can we measure force
- balancing it against a known force
- measuring the deformation of a material of known stiffness (F=kx)
- measuring an acceleration of a body of known mass (f=ma)
what causes force
electromagnetic: repulsion or attraction between electrical charges
gravitational: attraction between masses
how biological systems generate forces
when you bring two molecules together, their atoms can electromagnetically attract each other. this chemical bonding can cause molecules to pull on what ever they are attached to generating force.
how does myosin generate force
when myosin binds to actin, myosin goes through conformational change generating force on actin and whatever actin is attached too
The effects of adding sarcomeres in series vs. in parallel
series–> faster (muscle faster)
parallel–> more force (muscle stronger)
How and why muscle force depends on muscle length
The number of bound myosin “cross bridges” determines sarcomere force generation
- at longer lengths, the actin is spaced too far apart and myosin can’t reach actin binding sites.
- at shorter lengths actin filaments overlap likely interfering with some binding sites (rate of attachment decreases) causing myosin to produce force in the wrong direction
How and why muscle force depends on muscle velocity
Sarcomere force depends on its velocity
- force falls with shortening speeds because less xbs are bound, and some xbs are pulled into a region where they resist motion against those that are assisting
- high shortening velocities = no force
- lengthening velocities result in less bound xbs when compared to an isometric sarcomere, but the xbs are capable of more force per xb because they are stretching.
- the increase in force per xb outweigh the reduction in force due to less bound xbs
Why big muscles are stronger
- when muscles get bigger and stronger this is caused by an increase in the number of myofibrils which is caused by an increase in the number of myofilaments
- which increases the number of cross-bridges generating force within the muscle
so bigger muscle are stronger because they have more myosin generating force
how are scalers and vectors different
scalars: magnitude (distance and speed)
vectors: magnitude + direction (force, momentum, displacement)
define: ground reaction force
the force exerted by the ground on a body that is in contact with it
how do we measure ground reaction forces?
With force plates:
- measures forces and moments along 3 axes
- measures forces 1000/s
- strain gauges change their resistance as they are stretched or compressed
when a moment is CCW it is
positive
when a moment is CW it is
negative
why can muscles only “pull”
joints need antagonist muscles that generate joint moments of opposite sign to both flex, extend and stabilize joint
what is biomechanics
application of principles of physics to understand living systems
Explain why muscles are found in antagonistic pairs. Give an example of an antagonistic pair around a joint (other than the elbow joint) and explain how they would work together to allow a movement to occur.
- Because muscles can only pull
- example is quadriceps and hamstring
- the antagonistic pairs are connected with the joint and work with the joint to act as a lever. the fulcrum is the joint and the antagonistic pairs are at the end. this always us to flex and extend our muscles
