Levers
Synovial Joints: Fluid-filled cavity – synovial fluid Fluid is secreted by (1) synovial membrane, (2) articular cartilage and (3) “plasma” “Weeping lubrication” Bursae are separate, but have similar fluid
Synovial Joints: This is a DIAGRAM Actual cavity is really thin “Weeping lubrication”
Medial AND Lateral meniscus
Bones as levers
Just a Note This is NOT about physics It’s about WHY bones are they way they are Bones-joint ARE levers Math/physics is just a TOOL to help describe the way they work
This unit is exploratory This unit is exploratory. I provide essential background; you do the critical thinking!
Before We’re Done Look at skeletons and draw conclusions about their purposes Describe limbs have changed in adaptation to different niches Tremendous diversity from a common platform
Homology
Lever Effort Resistance Fulcrum
Fulcrum in the ‘middle’ Resistance in ‘middle’ Effort in ‘middle’
F R E
Class 3 Class 1
Class 1 Class 3
Class 2
Power vs.
Speed
Mechanical advantage = Deffort / Dresistance
Mechanical advantage = Deffort / Dresistance
It’s only a model…
Distance resistance moved It’s only a model… Model Effort Arm Resistance Arm Force needed to hold 100 g Distance Effort moved Distance resistance moved
Class 3
Fulcrum Effort Resistance Fulcrum is the stand Effort is the spring scale Resistance is the weight
Fulcrum Effort Resistance Measure distance from elbow to where biceps attaches and place spring at this distance Measure distance from elbow to middle of palm and place weight at this distance
Class 3
Fulcrum Effort Resistance Lift mass so it is parallel to table and record FORCE to hold if parallel How far did the effort MOVE? The resistance MOVE? Fill in table
Fulcrum Effort Resistance Move effort toward resistance and measure again Two more times What do your data indicate? Ratio? Pattern?
Work On Obj 1-5
Mechanical Advantage What does MA tell you? Diagram a lever, enter distances Work it out How about flexing your elbow?