Provides an in-depth look at three classes of levers. Has numerous real-life examples with informative diagrams. Also explores concepts such as mechanical advantage & disadvantage, torque, range of motion and other theories.
Definition: A lever is a rigid rod or mass that has the ability to do work when work is done
on it. A device for transmitting force.
The effort does work on the resistance.
Two different forces that act on them to create rotation about the fulcrum.
Fulcrum, effort, resistance (FER), e.g. elbow joint.
E
Skeletal
R
,levers:
● Functions of levers:
- Increase the effect produced when a force is exerted on a body.
- Increase the distance through which a body can be moved in a given time.
How do levers work:
● A force acting through a fulcrum (concentric force) has no leverage - exerts no
turning effort.
- Concentric force: any force applied to a fulcrum. Not the same as a concentric
muscle movement
No rotation (no
turning effect)
● A force acting any distance away from a fulcrum (eccentric force) has leverage -
exerts a turning effort.
- Eccentric force: any force applied a distance away from a fulcrum.
Eccentric force
d
Turning
effect/Torque
Torque/Turning effort:
● Kgs to Newtons. Kg multiplied by 9,81
, 1. The magnitude of the force is measured in Newtons.
- The size of the force contributes to the torque.
2. The perpendicular distance (⟂d) from the fulcrum that the force is applied.
How do levers work:
● Resistance (loads) cause lever arms to rotate about fulcrums and efforts (muscle
force do the same in the opposite direction.
● Turning effect depends on magnitudes of E & R and the distances of E & R from the
fulcrum.
● Turning effect of a force is the product of its magnitude and its distance from the
fulcrum.
First-class lever:
R
E
Effort Resistanc
arm e arm
TE = E X TR = R X ra
ea
The two must be
balanced
Muscles attached proximally to the distal segment. i.e. muscles are attached close to joints
(proximal), but far away from the part, they move (distal).
The forces of muscles are much greater than the force they lift.
Class three levers:
- Typical design of the human musculoskeletal system.
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