Forces and Torques lecture
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31 Terms
what is kinetics?
causes of motion
what is a force? what is the equation?
a push or a pull that produce, stops, or prevents a motion
F = m x a
what three factors are needed in a force vector?
magnitude, direction, point of application
what are the two types of external force? provide examples
non-contact
gravity
Contact
friction
ground reaction force (GRF)
what are some examples of ineternal force?
muscle contractions
ligaments
joint reaction force (JRF) (bone-on-bone)
explain and understand the forces in this picture
explain and understand the forces in this picture
explain and understand the forces in this picture
how to calculate weight? give formula
W = mg
are weight and mass the same thing? why or why not?
no because mass is the amount of mass the object has while weight is a force from the mass and gravity combined
gravity acts on your ______ __ ____.
center of mass
how do you decompose force vectors?
break it down into the vertical and horizontal components and then use SOH CAH TOA to solve
MEMORIZE THIS
(braking/propulsion) is always before (braking/propulsion).
Braking; propulsion
which part of the stance phase is braking and propulsion?
braking is the first part of stance phase while propulsion is the second part
in this picture, which phase do we see the braking and which phases do we see the propulsion?
1-3 is propulsion bc the arrow is going anteriorly
5-6 is braking bc the arrow is going posteriorly
* BEGINNING OF STANCE PHASE IS 5-6
what does the vertical loading rate line/slope tell you?
the foot has hit the ground and that is why vertical GRF is going up
when in the stance phase does the active peak happen?
in the MIDDLE of the stance phase
what happens (in terms of gait) when the vGRF hits 0?
it means toe off
there will be no GRF when the foot is off the floor
what is this a graph of?
HORIZONTAL GRF
which phase is the braking and how do you know?
5-6 because the arrow is POSTERIOR and POSTERIOR IS BRAKING
which phase is the propulsion and how do you know?
1-3 because the arrow is ANTERIOR and the ANTERIOR MEANS PROPULSION
why is there less of an impact peak with shoes on vs with shoe off?
the impact peak is less because the shoe foam cushions a lot of the force
the graphs for horizontal forces (A/P shear force) is flipped, which one is always first?
BRAKING IS ALWAYS BEFORE PROPULSION
what is pressure?
a force distributed over an area
what happens to the pressure when the same force is applied over a small area? what happens when it is applied over a large area?
small area = high pressure
large area = low pressure
what is the formula for pressure?
pressure = force/contact area
what is the pressure for wearing flats vs wearing high heels (assuming force is the same)?
flats would have a larger contact area which means lower pressure
high heels have a smaller contact area which means higher pressure
when applying it to vertebrae, why is the lumbar vertebrae larger than the cervical vertebrae?
the lumbar vertebrae supports the weight of our whole body so the contact area is greater to decrease pressure
the cervical vertebrae only holds our head and brain weight compared to how lumbar carries majority of our weight
what is torque? what is the formula?
a twisting force that tends to produce, stop, or prevent a rotational movement
T = F x ma
