The free-body diagram (FBD) of the 2 by 4 board is shown. If the beam is in equilibrium, then any portion of the beam that we choose to look at must also be in equilibrium. Therefore, the 2 by 4 segment shown above must be in equilibrium.
The free-body diagram (FBD) of the 2 by 4 board is shown. If the beam is in equilibrium, then any portion of the beam that we choose to look at must also be in equilibrium. Therefore, the 2 by 4 segment shown above must be in equilibrium.