Physics, Kinetics and Kinematics Flashcards
energy
the ability of an object to do work
potential energy
stored energy
kinetic energy
the energy of motion in an object
Force
F=m.a (newton’s 2nd law)
torque
- a rotational equivalent of force
- Rotates an object about an axis of rotation
torque is synonymous with
moment
what is the formula for torque
perpendicular force . length of lever arm. T=d/F
moment or moment of force
the tendency for a force to twist or rotate an object
internal moment
a rotational force-torque from within the body
examples of internal moment
muscles, ligaments, bony architecture
External moment
a rotational force from outside the body
Examples of external moment
ground reactive force, momentum, gravity
vector
forces associated with both magnitude and direction
motion at a joint partly depends upon
leverage
levers determine
mechanical advantage ( internal moment arm/ external moment arm)
in the 1st class lever the axis of rotation is located
between the opposing forces
an example of 1st class lever in the body
sagittal plane motion of the head is controlled muscle force and weight of the head
mechanical advantage in the 1st class lever
can be less than 1 , equal to or greater than 1
the axis of rotation in 2nd class lever is located
at one end of the bone
in the 2nd class lever the internal moment has ———leverage than the external moment
greater
example of 2nd class lever
rare in the body
mechanical advantage of second class lever
greater than 1
in the 3rd class lever the axis of rotation is located
at the end of the bone
what is the most common lever type in the musculoskeletal system
3rd class lever
3rd class lever has a mechanical advantage of
less than 1
friction
the force resisting motion of objects sliding against each other
momentum
the quantity of motion possessed by a body
linear momentum
mass. linear velocity
Rotational momentum
mass moment of inertia.angular velocity
newton 1st law
A mass is at rest until acted upon by an external force
law of inertia
a body in motion tend to stay in motion and a body at rest tends to stay at rest
inertia
resistance offered by an object to set it in motion,
moment of inertia depends on
the way the mass is distributed about the center of gravity
second law of newton
an external force will cause the body to accelerate in the direction of the force
relation of acceleration to force and mass
acceleration is proportional to the force and inversely proportional to the mass
work
force over distance in joules
power
rate at which work is done J/s
joint power
moment.angular velocity
centripetal force
a force that makes a body follow a curved path
centripetal acceleration
the rate of change of tangential velocity
angular acceleration
the rate of change of angular velocity over time
formula of angular acceleration
torque/mass moment of inertia
angular acceleration and centripetal acceleration are……
perpendicular
inverse dynamics
using kinematics and kinetics to calculate joint forces, torques and powers
each weight bearing limb accomplishes 4 functions
- propulsion
- stance stability
- shock absorption
- Energy conservation
energy conservation of the center of gravity
- pelvic rotation
- pelvic tilt
- knee flexion ( during loading response)
- foot mechanisms (ankle plantarflexion at heel strike)
- knee mechanisms ( knee extension with ankle plantar flexion after midstance)
- lateral displacement of the pelvis
in the inverted pendulum net work is
zero
in the inverted pendulum net work is zero because
positive and negative work cancel each other out
in walking PE and KE are
out of phase
we have minimum PE when
COM is at its lowest point (DLS)
we have maximum PE when
COM is at its highest point (SLS)
minimum KE when
COM is at its highest point
Max KE when
COM is at its lowest point
in DLS leading limb performs
negative work (inealstic collision with ground)
following limb perform
positive work
both limbs perform———and ———-work against each other simultaneously
positive
negative
DLS lasts for ——-of gait cycle
20%
DLS accounts for ———-of metabolic energy through muscle activity
60%-70%
2 of the 3 rockers are active during DLS -redirects __________and preserves ___________
center of mass velocity
Forward momentum
gastrosoleus complex is AKA
tricep surae
the COM is thought ti be anterior to
S2
the center of gravity implies a ———having magnitude and direction, changes with———–
Force
position of the body
COM ——-COG
does NOT equal
forefoot rocker
propulsive phase
ankle rocker
midstance
heel rocker
heel strike/loading response
kinematics
study of motion
linear motion gives
distance
velocity
acceleration
rotational motion around an axis gives
angular displacement
angular velocity
angular acceleration
kinetics
study of forces, masses, and moments
forces that cause movement
internally through
muscle activity
ligaments
friction of muscle and joints (bony architecture )
externally through
ground
active or passive bodies (primarily GRF, momentum and gravity)
forces are
vector quantities with magnitude and direction
scalar quantities
like temp and mass only have magnitude
for forces generated from rotational motion you need to know
momentum
mass
force
for forces generated from rotational motion, you need to know
angular momentum
moment of inertia
moment
moment
M=F.D
Ground reactive force create external moments how does the body react to that?
the body reacts by creating internal moment through muscle contraction, tension in soft tissues (eg ligaments ) and bone to bone forces
moment of inertia deals with
rotational motion
moment of inertia has to do with
HOW the mass is distributed in the limb segment
what is couple in kinetics
a moment created by 2 equal forces parallel to each other , but acting in opposite directions
an example of couple
plantarflexion-knee extension in terminal stance
gait rite system
gives measures such as
- step variability
- step length
- step time
- cadence (rhythmic)
- walking speed
Simi System Cycling
motion analysis-how much range of motion occurs in the knee?
What are the 3 rockers?
Heel rocker
Ankle rocker
Toe rocker
