Final answer:
In the falling-dominoes analogy for nuclear fission, the domino effect mimics the neutron-induced chain reaction of uranium nuclei, while a metric ruler represents the control mechanisms, like control rods, necessary for managing this reaction.
Step-by-step explanation:
In the falling-dominoes model of a nuclear fission chain reaction, the striking of one domino by another represents a neutron hitting a uranium-235 nucleus, causing it to split and release more neutrons. These additional neutrons then strike other uranium-235 nuclei, continuing the series of reactions. This sequence of events reflects the concept of critical mass, which is the smallest amount of fissile material needed to sustain these reactions at a constant level.
The metric ruler in this model would represent controls used in managing a nuclear reaction, such as control rods in nuclear reactors. These rods absorb neutrons and can adjust the rate of the chain reaction, ensuring it remains controlled. In a nuclear reactor, maintaining the reaction at a steady pace is necessary for sustainable energy production, whereas an uncontrolled reaction can lead to an explosion, as seen in nuclear weaponry.