Functional Anatomy Week 6 Flashcards
Centric force
What does it produce
External force directed through an objects centre of gravity
Acts to prduce linear motion
Eccentric force
What does it produce
An external force not directed through an objects centre of gravity
-Acts to produce linear and angular motion
Force couple
Forces that are equal in size but opposite in direction and do not act n the same line
Torque
The rotatory force when the line of action of a force does not pass through the axis of rotation
Moment arm
The perpendicular distance between the line of action of the force and a parallel line passing through the objects axis of rotation
Torque equation
Torque = force x moment arm
Units = N/m
Components of a lever
A lever consists of a rigid bar (bone) that rotates about a fulcrum (joint - axis of rotation)
Levers also involve ‘effort’ forces (muscles) that act to counteract ‘resistance’ forces (weight/external pushes)
Lever systems are used to generate torques onto the joints and rotate our limbs.
How to work out mechanical advantage
Length of force (or effort) arm/length of resistance arm
Remember torque = force x moment arm
1st class lever
Fulcrum in the middle with effort and resistance on either side
Example is nodding head on neck
Mechanical advantage of a 1st class lever`
Mechanical advantage may be high or low depending on the length of the force arm in relation to the resistance arm
2nd class lever
Fulcrum on one side, resistance in the middle, force on the other
Example is plantar flexion
Mechanical advantage of a 2nd class lever
Always have a high mehcanical advantage (>1) because the force arm is longer than the resistance arm
3rd class lever
Fulcrum on one side, force in the middle
Example is elbow flexion
What are third class lever systems designed for?
Speed and range of movement
What must happen for an object to be in static equilibrium
Both the external forces and external torques, about the axis, must sum to 0
