Biomechanics: Simple Machines

Question 1

Define lever

Answer 1

a rigid bar that can rotate about a fixed point when a force is applied to overcome resistance

Question 2

Define force arm (FA)

Answer 2

distance between force and axis

Question 3

Define resistance arm (RA)

Answer 3

distance from axis to resistance

Question 4

Define axis

Answer 4

the fixed point around which the lever rotates

Question 5

Equation for levers, distances

Answer 5

Force * Distance to Axis = Resistance * Distance to Axis

Question 6

Equation for levers, displacement

Answer 6

Force * displacement (distance to axis times sin angle) = resistance * displacement (distance to axis times sin angle)

Question 7

Define mechanical advantage for levers

Answer 7

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

Question 8

Define a first class lever

Answer 8

axis is between force and resistance

Question 9

What are some examples of a first class lever?

Answer 9

balance, see-saw, scissors, neck extension, triceps

Question 10

What is the advantage of a first class lever?

Answer 10

can be designed for either ROM or Power

Question 11

Define a second class lever

Answer 11

resistance is between axis and force

Question 12

What are some examples of a second class lever?

Answer 12

wheelbarrow, nutcracker, plantar flexion (tiptoes)

Question 13

What is the advantage of a second class lever?

Answer 13

power, FA>RA

Question 14

Define a third class lever

Answer 14

force between axis and resistance

Question 15

What are some examples of a third class lever?

Answer 15

hammer, biceps

Question 16

What is the advantage of a third class lever?

Answer 16

range of motion, FA

Question 17

Define pulley

Answer 17

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

Question 18

Define mechanical advantage for pulleys

Answer 18

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

Question 19

Describe a fixed pulley

Answer 19

attached to a beam, rope is n shaped

Question 20

What are some examples of a fixed pulley?

Answer 20

elevator, flag pole, medial malleolus and tendon of peroneus longus

Question 21

What is the advantage of a fixed pulley?

Answer 21

can change the direction of force (MA=1)

Question 22

Describe a moveable/suspended pulley

Answer 22

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

Question 23

What is the advantage of a moveable/fixed pulley

Answer 23

increases the amount of force at the cost of high distance, but cannot change the direction of the force (MA=2_

Question 24

Define wheel and axle

Answer 24

a wheel with a crank attached that helps increase force

a grooved wheel turned with a cord/chain with a fixed axle

Question 25

What is the mechanical advantage of a wheel/axle?

Answer 25

Lever in disguise, Radius of Wheel / Radius of Axle

Question 26

Define inclined plane

Answer 26

a flat surface that slants to create more distance with less effort

Question 27

What is the mechanical advantage of an inclined plane?

Answer 27

ratio of the length of the slope to the height of the slope

Question 28

What are the three main types of simple machines?

Answer 28

lever, inclined plane, pulley

Question 29

What is a harmonic drive made of?

Answer 29

a fixed circular spline, a flex spline (output), and a wave generator (input)

Question 30

What is the mechanical advantage of a harmonic drive?

Answer 30

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)