BIOL 325 - Forces & Levers

Levers

• Rigid object that can pivot (rotate) around an axis

• amplify force OR distance 

• 3 types based on the position of effort, load, fulcrum 

Mechanical Advantage (def, formula)

• Force amplification/reduction by lever due to the relative lengths of the effort and load arms 

• = F_L/F_E = d_E/d_L

Distance Advantage (def, formula, speed?)

• Distance amplification/reduction by lever due to the relative lengths of the effort and the load arms. 

• = F_E/F_L = d_L/ d_E

• similar to speed advantage ( 4x speed = 4x distance)

Lever 1st Class (def, relation, eg) [LFE]

• Fulcrum between effort and load

• d_L <, > or = d_E

• eg: scissors, crowbar

• Only class where MA = DA = 1

Lever 2nd Class (def, relation, eg) [FLE]

• load between fulcrum and effort 

• d_L< d_E

• eg: wheelbarrow, bottle opener 

Lever 3rd Class (def, relation, eg) [FEL]

• Effort between load and fulcrum 

• d_L > d_E

• eg: most in skeletal system 

Relationship between MA & DA

• MA = 1/DA

• if MA > 1, then DA < 1 & vice versa

Torque (τ - tau) (def, formula, direction, angle of moment arm)

• measure of force that causes an object to rotate about an axis

• = Force (N) x length of the moment arm (m) = F x d (N m)

• Counter Clock Wise (CCW) - +ve

• Clock Wise (CW) - -ve

• the moment arm should be perpendicular to the line of action of the force