Linear Kinetics Flashcards
What do we need to know to adequately describe a force?
- magnitude
- direction
- point of application
mass (kg)
amount of matter constituting the body
weight (N)
mass * gravity
F = M*a
center of mass
point about which the matter of a body is evenly distributed
object supported by _____ will balance and rotate freely
COM
T or F? COM may be in a location with no mass
true
COM - the point about which the sum of torques =
zero
law of inertia
every body at rest, or moving at a constant velocity in a straight line will continue in that state unless compelled to change by an unbalanced external force exerted upon it
movement is ____ in the absence of a net external force
constant
momentum =
m*V
law of acceleration
the acceleration of a body is proportional to the net force causing it and takes place in the direction in which the net force acts
SumF = m*a
law of action/reaction
for every force that is exerted by one body on another, there is an equal and opposite force exerted by the second body on the first
- for every action there is an equal and opposite reaction
joint reaction force
- equal and opposite forces that exist between adjacent bones at a joint caused by the weight and inertial forces of the two segments
- the net force acting across the joint
what are the internal forces resolved into components?
- rotary (shear)
- stabilizing (compressive)
- dislocating (tension)
what is the primary external force we’re concerned with?
gravity! it’s inherent in pt. evaluation and exercise prescription
- effect of gravity on joint torque will vary throughout the range of motion
acceleration of an object occurs only when there is an _____-
imbalance of force
what are two types of forces acting on a system?
- linear motion
- rotation and or translation motion
what are two types of rotation and or translation motions?
- eccentric
- force couple
What are two examples of force couples?
- humeral rotation without translation (most muscles do this)
- scapular rotation without translation (raise arm above head)
T or F: muscles produce force of 5-15x greater than body weight to accelerate COM against gravity
True
joint forces in the body are much greater than vGRF (gravity)
Impulse =
force * time
(often calculated as the integral (area) under the force-time curve
momentum =
mass * velocity
F = ma or….
F= m ((change v)/(t))
Ft = m(change v)
Ft = momentum final - momentum initial
speeding up _________ impulse and _______ change in velocity of COM(for ant/post)
increases
increases
slowing down _____ impulse and ______ change in velocity on COM (for ant/post)
decreases
decreases
___________ impulse with each stance phase accelerates CoM left and right
medial
* known as serpentine pattern
what is the only force that exists in presence of another force?
friction
what is the force that resists sliding/slipping
friction
T or F: there can be friction without movement
true
Where does friction act?
at the point(s) of contact between contacting surfaces
- always opposes motion between contacting surfaces
friction magnitude is ________
variable
static friction
resistance prior to sliding
Fs is equal to
motive force
kinetic friction
resistance one sliding occurs
Fk is less than
motive force
What are the factors affecting friction?
coefficient of friction
normal force
Friction force =
(what is the formula)
u*N
what does normal force do?
forces holding surfaces together
is perpendicular to the supporting surface
