def sound_intensity(pressure, velocity):
    """
    Sound intensity :math:`\\mathbf{i}`.

    :param pressure: Sound pressure :math:`p(t)`.
    :param velocity: Particle velocity :math:`\\mathbf{u}(t)`.

    .. math:: \\mathbf{i} = p(t) \\cdot \\mathbf{u}(t)

    """
    return pressure * velocity
