Angular Kinetics 2 Flashcards
What is angular force?
- eccentric force: away from CoG
- turning effect –> torque
- a force tending to cause rotation around a fixed point
The shorter the moment arm, the ____ (more/less) torque on the system.
less
Describe levers.
- hinged, rigid structures
- hinged point = axis of rotation (fulcrum)
What is the force causing motion in a lever called?
F (or motive force: MF)
What is the force acting in opposition in a lever called?
R (or resistance force: RF)
Where is the fulcrum, F (motive force), and R (resistance force) in a 1st class lever?
- fulcrum/axis in middle
- downwards motive force on one side
- downwards resistance force on the other
Give examples of 1st class levers.
- see-saw
- atlanto-occipital joint
Where is the fulcrum, F (motive force), and R (resistance force) in a 2nd class lever?
- fulcrum/axis on one side
- upwards motive force on the other side
- downwards resistance force in the middle
Give examples of 2nd class levers.
- wheelbarrow
- ankle when on tip toes
Where is the fulcrum, F (motive force), and R (resistance force) in a 3rd class lever?
- fulcrum/axis on one side
- upwards motive force on the same side
- downwards resistance force on the other side
The greater the forces acting on a lever system, the ______ (greater/less) tendency to cause rotation and the _____ (greater/less) angular rotation.
- greater
- greater
The greater the distance between the two forces (F and R) in a lever system, the _____ (greater/less) the turning effect (torque).
greater
A lever of any class will balance when…
the product of the force arm (FA, from F to fulcrum) and the force (F) is equal to the product of the resistance arm (RA, from R to fulcrum) and the resistance (R):
FA x F = RA x R
Mechanical advantage (MA) increases as…
the FA gets larger than the RA
Shorter levers are ______, while longer levers are ______ .
- faster
- stronger
Describe the ARF where the lever is an arm held at a 90 degree angle holding a dumbbell.
- Axis of rotation (fulcrum): elbow
- Resistance Force: dumbbell weight x gravity (Newtons)
- Motive Force: bicep muscular contraction upwards
What is angular inertia?
property of an object to resist changes in its angular motion
Name the 2 factors that affect angular inertia.
- mass
- distribution of mass
Ia would be greater when:
- greater mass (heavier)
- mass is further away from the axis of rotation
What is the moment of inertia (I)?
quantity of angular inertia
Distribution of mass is also referred to as…
radius of gyration (k)
What is the radius of gyration (k)?
Distance from axis of rotation to a point at which the mass of the body can theoretically be concentrated without altering the inertial characteristics of the rotating body
What is angular momentum (H)?
the product of the angular inertial property (moment of inertia) and angular velocity
What are the 3 factors that affect angular momentum (H)?
- mass
- distribution of mass
- angular velocity
Is mass, length (radius of gyration), or angular velocity more important in calculating angular momentum?
length (radius of gyration)
What is the conservation of angular momentum?
the total angular momentum of a given system remains constant in the absence of external torques
Does gravity affect the angular momentum of a body rotating in the air? Why or why not?
- no
- gravitational force acts through the CoG, therefore, there is no torque (eccentric force)
Can an athlete add angular momentum once their body has left the ground?
no
In order to speed up or slow down rotation once their body has left the ground, the athlete must…
redistribute mass (lengthen or shorten k – tuck legs in, fold into pike, etc.)
Once the body has left the ground, _____ must change to conserve angular momentum.
angular velocity (ω)
