def eq_of_motion(t, w, p):
    """ A simple mass with a force input 
    
    Arguments:
      w : the states, [x, x_dot]
      t : the current timestep
      p : the parameters
        p = [m, curr_force]
    
    Returns:
      sysODE : 1st order differential equations
    """
    
    m, curr_force = p
    
    sysODE = [w[1],
              1.0 / m * curr_force]
    
    return sysODE