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Translational and rotational degrees of freedom
Skeletal joints are largely rotational.
Rigid bodies connected at joints with up to 6 degrees of freedom.
What are 1-, 2- and 3-DoF joints?Any translational joints?
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cruciate ligaments constrain knee motions
synovial membranearticular
cartilage
weeping lubricationcoefficient of frictionknee joint ~0.003good ball bearing ~0.02
What restricts degrees of freedom?
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Rotational motion, torques and energy
angle
angular velocity
angular acceleration
torque
angular momentum
moment of inertia
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Rotational motion, torques and energy
torque
Torque and energy have the same units? Are torque and energy the same thing?
No.
equilibrium
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Rotational motion, torques and energy
torque
Torque and energy have the same units? Are torque and energy the same thing?
No.
Torque is force applied perpendicular to a lever arm.
Work is force applied along a distance.
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Types of levers
1st class 2nd class 3rd class
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The trade-off between force and speed
mechanical advantage speed ratio
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Which class of lever are these legs?
Which has a higher speed ratio? mechanical advantage?
What can you infer about the function of these limbs? Which animals might they belong to?
1st class 2nd class 3rd class mech adv speed ratio
The trade-off between force and speed
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4 bar linkage
5 bar linkage
6 bar linkage
More complex levers: linkages
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Fin
Fout
r q
Force amplification ~ r/q Speed Amplification ~ q/r
More complex levers: linkages
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Linkages in nature
Cranial kinesis in birds,reptiles, and amphibians.