ANGULAR KINEMATICS Flashcards
most human movements are based on what type of motion
angular
-translation of the human body happens via rotations of our joints
angular units
-degrees
-radians
-revolutions
what unit must angular quantities be in to translate into a linear quantity
radians
1 radian = ___ degrees
57.3
1 revolution = ___ degrees
360
1 revolution = ___ radians
2pi
angular displacement is a scalar or vector
vector
angular displacement
rotations in the clockwise direction have what sign
negative
angular displacement
rotations in the counterclockwise direction have what sign
positive
angular velocity is a scalar or vector
vector
angular acceleration is a scalar or vector
vector
angular displacement
distance the point has traveled along the arc length
the greater the radius of rotation, there is less/more LINEAR distance undergone by that point during angular motion
more linear distance traveled
ex: swinging a baseball bat
describe angular + linear displacements of points near handle + end of bat
-points near handle + end of bat are moving the same ANGULAR displacement
-points near handle move less LINEAR displacement than points at end of bat
ex: bike gearing
describe angular + linear displacements at different points of gear
-must have equal LINEAR displacements because connected by a chain
-ANGULAR displacement is different now
tangential velocity
linear velocity at an instant in time
-must be tangent to curve
what does radial acceleration cause
causes the change in direction of the linear/tangential velocity
what is radial acceleration directed towards
center of rotation
when is radial acceleration present
when angular velocity is non-zero
-doesn’t matter what angular acceleration is
centripetal force
keeps body on a curve trajectory
what does centripetal force cause
radial acceleration of the body in motion
in the case of a bicyclist, what is the centripetal force
friction; it keeps bike from slipping during a turn
tangential acceleration
-directed tanget to the curve
-perpendicular to the radial acceleration
when is tangential acceleration present
when angular acceleration is non-zero
describe angular acceleration of a figure skater doing revolutions
as their revolutions per second increase over time, they will have a non-zero angular acceleration, which produces linear tangential acceleration for a given point on their body
total linear acceleration
the vector composition of the radial + tangential accelerations
if an object is orbiting at a constant angular velocity is angular acceleration zero?
angular acceleration is zero
if an object is orbiting at a constant angular velocity is linear acceleration zero?
linear acceleration is not zero because we have radial acceleration, which is a component of linear acceleration
what happens if tangential acceleration + tangential velocity are in opposite directions
object is slowing down
is it possible to have zero radial acceleration and non-zero tangential acceleration
-if you have zero radial acceleration, angular velocity must be zero
-you can still have non-zero tangential acceleration for a MOMENT IN TIME
general motion involves…
combination of rotation + translation
what is true of 2 connected bike gears of different size radii
-the angular displacement of the gears must be equal
-both the linear distance traveled by points A + B as well as the angular displacements of the gear must be equal
-the linear distance traveled of points A + B on their edges must be equal
the linear distance traveled of points A + B on their edges must be equal
if someone changes their rotational direction which of the following are true about the moment of transition from rotating one way to the other way? (mark all that apply)
-radial acceleration is 0
-angular acceleration is 0
-angular velocity is 0
-tangential acceleration is 0
-radial acceleration is 0
-angular velocity is 0
true/false: during mid single leg stance of walking gait the hip reaches its most extended angular position
false
during the gait cycle the deepest knee flexion angle occurs during what phase/event of the gait cycle?
-absorption of momentum following heel strike
-initial contact (heel strike)
-early/mid swing
-mid stance
-instant toe off
early/mid swing
true/false: when you use an angular to linear conversion equation (ex: v=rw) it is important to keep the sign (-/+) of the result because it tells you the direction of the resulting linear vector
false; the equations only give you the magnitude of the linear quantity
true/false: the ankle is dorsiflexing (moving towards dorsiflexion) as the walker appraches mid swing
true
when is the hip maximally flexed
from terminal swing to initial contact
when does the hip reach max extension
at opposite initial contact
when does the knee reach max extension
at heel rise
when does the knee reach max flexion
during initial swing
when does ankle reach max plantarflexion
right after toe off
when does the ankle reach max dorsiflexion
during terminal stance + swing
