sentences:  The generalized force gives the work done
  
  where the index formula_6 runs over the formula_7 generalized coordinates formula_3, which usually correspond to the degrees of freedom of the system.The function formula_9 is defined as the mass-weighted sum of the particle accelerations squared,
  
  where the index formula_11 runs over the formula_12 particles, and
  
  is the acceleration of the formula_14-th particle, the second time derivative of its position vector formula_15.Each formula_15 is expressed in terms of generalized coordinates, and formula_17 is expressed in terms of the generalized accelerations.