Popsicle stick chain reactions

Prep Work

1. Make a piece to start your chain by placing three tongue depressors parallel to each other. Leave about two centimeters between the depressors.
2. Stagger the parallel depressors so each depressor sticks out two to three centimeters above the adjacent one.
   
3. Place a depressor at a right angle to all three depressors. Shift it until it just touches all three depressors, and glue it in place.
   
4. Place a second depressor next to it and glue it to all three staggered depressors.
   
5. Turn over and glue two depressors on the other side to help keep the three staggered depressors in place.
6. Number the depressor that sticks out most 1, write 2 on the middle one and 3 on the one that sticks out least. You can color the starting piece with markers as shown below. Colors are not essential but can help you understand how to assemble the chain.
   

Procedure

1. To start your chain, have the starting piece that you just assembled and a large number of tongue depressors nearby. You may want to color a few depressors in four different colors as shown in the picture. This may help you get started.
   
2. Slip a depressor in the starting piece so it goes under depressor 1, over depressor 2 and under depressor 3.
   
3. Slip the next depressor in the starting piece so it goes over depressor 1, under depressor 2 and stops there.
   
4. You should see two parallel depressors sticking out.
   
5. Slip the next depressor under the shorter one until it sticks out a little, and over the longer one, parallel to depressor 1.

   You might feel you have to hold the depressors in place. Why would this be?

   
6. You should see two parallel depressors sticking out.
   
7. Slip the next depressor under the shorter one until it sticks out a little, and over the longer one so it makes a right angle with the sticks it crosses.
   
8. Find the two parallel depressors sticking out and slip the next depressor under the shorter one until it sticks out a little, and over the longer one so it makes a right angle with the depressors it crosses.
   
9. Repeat step 8 to build on.

   Do you feel like you have to bend the depressors? How would that help create an explosive chain reaction? What do you think will happen when you no longer hold down the last couple of depressors you weaved into the chain?

   
   
10. If finding the two parallel depressors that are sticking out is hard, you can also rely on the colors to build the chain. Notice how in these pictures, the sequence is red, light blue, orange, dark blue and then back to adding a red depressor. In this case, the red depressors always go under a dark blue one and over a light blue one. Orange depressors go over the dark blue and under the light blue ones or light blue depressors go under red and over orange ones, etc.
11. Keep building until you are satisfied with the size of your creation. You can keep the depressors in place by fixing the last depressor you are adding under the one that would be parallel to it if you were continuing making the chain longer.
    
12. Once you are ready, let the last depressor go, but be ready to step back and watch.

    What happens? Why would this happen?

13. Build longer chains and see how the chain reaction changes as the chain gets longer. If you have a video camera available, take a video of the chain going off, preferably in slow motion.

    What is different and what is similar between a longer and a shorter chain reaction? What can you learn from the slow-motion video?

    
14. For a challenge, make your stick bomb make a bend or make it go over obstacles.

What Happened?

You probably saw the depressors jump up in the air as soon as you release the last one, and maybe even before you planned to let them go.

You may have noticed that you had to bend the depressors in order to make them fit into the chain. With each bend, you added energy to the system. Did you feel how the chain was under tension, how you had to hold the last couple of depressors to keep them in place? When you let it go, all this tension is released in a chain reaction. It starts with the last depressors straightening up. This releases the next depressors in the chain, and so on. Soon, all the depressors fly in the air, releasing the energy stored in them and you have a whirlwind of depressors flying around.