Quiz #13 Flashcards
Lever
Fulcrum
- Effort force, Effort arm
- Resistive force, Resistive arm
lever
Levers:
Classified according to the relative positions of the _, effort force and resistive force
fulcrum
MA >1 = _
MA <1 = _
- mechanical advantage
- mechanical disadvantage
- Axis between effort force and resistive force
- May act with or without a mechanical advantage
- see-saw, elbow extension, head extension
1st class lever
cervical flexion/extension
1st class lever
- Resistance in between mechanical advantage
- Not as versatile as 1st class lever
- push-up, wheelbarrow
2nd class lever
Calf raise
2nd class lever
- effort force in middle
- mechanical disadvantage
3rd class lever
knee extension
3rd class lever
Anatomical levers:
muscle usually has a _ _ _ (inserts close to axis)
- this provides an advantage for increasing range of motion and velocity of distal points
- however, it also produces a mechanical disadvantage (MA<1)
- thus, muscle forces generated must be in excess of resistant forces
small effort arm
Anatomical levers:
Force of muscles can be resolved into two components:
1. on perpendicular to the attached bone
- this produces _
2. one parallel to the bone
- this produces _
- torque
- stabilizing or dislocating force
With no external force acting on an object that object wants to:
- not move if it wasn’t moving to begin with
- angular
- object continues rotating at constant speed (assuming the rigid body)
- angular momentum of an object remains constant unless a net external torque is exerted on it
- the principle of conservation of angular momentum
Angular Analog Newton’s First Law
Angular momentum:
- rigid object: Ha=Ia(t)a
- no external force causing rotation acts on spoon, therefore (t) remains _
- gravity - acts through the spoon’s center of mass
constant
Angular momentum:
- non rigid object: Ha=Ia(t)a
- according to Newton’s first law angular momentum remans constant
- therefore, if I changes (t) will _
change
A net external torque causes
- the object to angularly accelerate in the direction of the net external torque
- the object’s angular acceleration to be directly proportional to the net external torque and inversely proportional to its moment of inertia
- Net joint torque - torque necessary to produce the segmental acceleration present
Angular Analog Newton’s Second Law
For every action there is an equal and opposite reaction
- for every torque exerted by one body on another body, there is an equal and opposite torque exerted by the latter body on the former
Angular Analog Newton’s Third Law
Angular Impulse:
- A net angular impulse causes a change in _ _
- while in air long jumper swings legs clockwise the upper body counteracts by rotating counterclockwise
- muscles cause torque on both ends of segment
angular momentum
Twisting:
While in flight
- although angular momentum remains constant (no net torque); transferring angular velocity from on axis of rotation is possible
Body twist technique
Twisting:
While in flight
- even when total angular momentum is 0, generating a twist in midair is possible when the body is composed of at least 2 segments
Cat twist technique
The product of the force applied to a body and the displacement of the object
work
Work:
U=F*d
- direction of force parallel to line of displacement
mechanical perspective
Work:
U=Fcos^-1d
- direction of force not parallel to line of displacement
- equal angle between displacement and line of application
Physiological perspective
To determine the amount of work being done, need to know:
- the average force exerted on the object
- the direction of this force
- the displacement of the object along the line of action of the force during the time the force acts on the object
