Question

In your falling-dominoes model of nuclear fission chain reactions, what did a
standing domino represent? What did the fall of a domino represent?

Answer 1

1. Stand 15 dominoes in a single straight row in such a way that the distance between them is about one half of their height. Knock over the first domino. Measure and record the time it takes for all the dominoes to fall.
2. Repeat Step 1 two more times. Then, average the three time measurements to get a more accurate
time.
3. Arrange 15 dominoes in curved rows with one domino at the center, two in the next row, four in the next row, and eight in the next row, so that each domino will knock over two others. Observe what happens when you knock over the first domino. Measure and record how long
it takes for the whole set of dominoes to fall over.
4. Repeat Step 3 two more times. Average the three time measurements to get a
more accurate time.
5. Set up 15 dominoes again as you did in Step 3. This time, however, hold a metric ruler on end, in the middle of the arrangement of dominoes. Knock over the first domino. Observe what happens.
6. Set up 15 dominoes as you did in Step 3, but this time, place 5 additional dominoes behind and at right angles to 5 randomly chosen dominoes for support. The 5 supported dominoes represent atoms of a different isotope that must be struck with more energy to undergo fission.
7. Knock over the first domino. Measure and record the time it takes for the dominoes to fall and how many dominoes fall.
8. Repeat Steps 6 and 7 two more times. Then, average the three time measurements to get a more
accurate time.
9. Repeat Steps 6 through 8, but this time, place supporting dominoes behind only 3 dominoes.
10. Repeat Steps 6 through 8, but this time, place a supporting domino behind only 1 domino.