This has been a bit of a problem for me for a while. My research is in ultrasonic vibrations and this question I have relates to a vibrating beam I am working with. I have a free-free beam vibrating transversely and I know what the accelerations along the beam are. On the beam are feet at two different locations that impact the ground. If there were only one foot impacting the ground I would say that the resulting normal force would simply be: N=(m_totalbeam)*-(accel_foot) But since I have two feet how do you divide up the mass? Essentially, if the bar's feet hit the ground with 2 different accelerations, what would each resulting normal force be? Would each foot be 1/2 the total mass times the acceleration of the foot? Would I have to calculate the mass from the foot to the nearest node?