Biomechanics: Simple Machines Flashcards
Define lever
a rigid bar that can rotate about a fixed point when a force is applied to overcome resistance
Define force arm (FA)
distance between force and axis
Define resistance arm (RA)
distance from axis to resistance
Define axis
the fixed point around which the lever rotates
Equation for levers, distances
Force * Distance to Axis = Resistance * Distance to Axis
Equation for levers, displacement
Force * displacement (distance to axis times sin angle) = resistance * displacement (distance to axis times sin angle)
Define mechanical advantage for levers
the ratio of the length of the lever on the applied effort side of the fulcrum to the length of the level on the load force side of the fulcrum
OR
ratio between the force arm and resistance arm or between the output force and input force
MA=FA/RA=R/F
Define a first class lever
axis is between force and resistance
What are some examples of a first class lever?
balance, see-saw, scissors, neck extension, triceps
What is the advantage of a first class lever?
can be designed for either ROM or Power
Define a second class lever
resistance is between axis and force
What are some examples of a second class lever?
wheelbarrow, nutcracker, plantar flexion (tiptoes)
What is the advantage of a second class lever?
power, FA>RA
Define a third class lever
force between axis and resistance
What are some examples of a third class lever?
hammer, biceps
What is the advantage of a third class lever?
range of motion, FA
Define pulley
a grooved wheel that turns on an axle with rope/cable and can change the direction of force or change the magnitude of a force
Define mechanical advantage for pulleys
the amount of extra rope to move the object
the reciprocal of the amount of force needed to move the object
ratio of tension(s) to resistance
Describe a fixed pulley
attached to a beam, rope is n shaped
What are some examples of a fixed pulley?
elevator, flag pole, medial malleolus and tendon of peroneus longus
What is the advantage of a fixed pulley?
can change the direction of force (MA=1)
Describe a moveable/suspended pulley
one end of the rope is attached to a beam then the rope is ran through the pulley and force is applied at the other end, rope is U shaped
What is the advantage of a moveable/fixed pulley
increases the amount of force at the cost of high distance, but cannot change the direction of the force (MA=2_
Define wheel and axle
a wheel with a crank attached that helps increase force
a grooved wheel turned with a cord/chain with a fixed axle
What is the mechanical advantage of a wheel/axle?
Lever in disguise, Radius of Wheel / Radius of Axle
Define inclined plane
a flat surface that slants to create more distance with less effort
What is the mechanical advantage of an inclined plane?
ratio of the length of the slope to the height of the slope
What are the three main types of simple machines?
lever, inclined plane, pulley
What is a harmonic drive made of?
a fixed circular spline, a flex spline (output), and a wave generator (input)
What is the mechanical advantage of a harmonic drive?
Gear reduction produces a mechanical advantage
Sacrifice distance to gain force
Reduction Radio →
(teeth on flex spline - teeth on circular spline) / (teeth on flex spline)
