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Chain reaction

By David, 21 August 2013 Activity

In this hands-on activity you’ll create a chain reaction with boxes, and learn about radiation released from decaying atoms.

You will need

A stack of boxes. From the bottom: a jigsaw puzzle, a hardcover book, a science kit, a bar of chocolate, a box of jelly beans, some sore throat lollies, small candies, an eraser.

Make sure each box is a bit bigger than the one before it.

  • Boxes of different sizes. The best boxes for this activity are tall and skinny, like a deck of cards on its end, or a box of cereal. Try to get the biggest range of sizes that you can.

What to do

  1. Take the smallest box that you have and put it on its end.
  2. Take another box that is a bit bigger and put it in front of the last box, quite close to it. You want the smaller box to be more than half the height of the bigger one.
  3. Tip the smaller box over so it hits the larger box. Hopefully this will cause the larger box to fall over too.
  4. Set the boxes up again, and then find an even larger box to put in front of the next largest box. Try knocking over the small one again – hopefully all three of them fall over, one after the other.
    several boxes, all standing on end.

    Set up the boxes with a small gap between each box

  5. Keep adding bigger and bigger boxes until you can’t find any bigger ones. Then try tipping over the smallest box to set off the chain. The little box will eventually make the big box fall over!
  6. If one of the boxes is not knocking over the next box, here are a couple of things you could try to make the chain work better:
  • Try to find a box that is in-between the two problem boxes in size.
  • Try putting a bit of play-doh or plasticine on top of the smaller box to make it heavier.
  • Move the two boxes further apart or closer together.
    several boxes all standing on end. the ones on the left have fallen over, and are knocking over the ones on the right.

    Hopefully, tipping over the smallest box will eventually knock over the largest one!

What’s happening?

When you put a box up on its end, it is in an unstable position. A relatively small push will make it fall over, and when it does, it will get more energy from falling than it took to knock it over in the first place. This means that each box in the chain can push over larger and larger boxes, and a very small box can eventually cause a large box to fall over.

As long as you can find boxes of the right size and weight, you should be able to double their weight every step. If you kept adding boxes, each one twice as heavy as the last, there would only need to be 17 boxes between a pack of tic-tacs and a large car standing on its end.


An atom of a radioactive element will eventually decay, turning into one or more different atoms and releasing energy. However, this spontaneous decay takes too long to be used for electricity generation. In a nuclear power plant, there is another type of nuclear reaction going on.

Some types of radiation can make certain atoms unstable, which can cause them to decay straight away. When they do, they give off more radiation. Because a lot more decays are happening, a lot of energy is released, and that energy can be used to run nuclear power plants. Engineers can control the speed of the reaction by changing the temperature of the reactor or by adding special substances that soak up radiation.

Some decaying atoms release enough radiation to cause two or more other atoms to decay. If there are a lot of these atoms in a very small space, the reaction can keep increasing out of control. Much of the fuel will decay in a fraction of a second, releasing a huge amount of energy and causing a nuclear explosion. Nuclear power plants do not contain enough fuel, or good enough fuel to cause a nuclear explosion. However, if the core gets too hot, it can melt the fuel, which can cause many other problems.

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