Make a hanging mobile

This guide shows you how to make a very special kind of mobile. It is made entirely from paper, and for this reason it is very light. For this activity you will need both normal scissors and a smaller pair of scissors (such as nail scissors or hair scissors). The finished model looks like this:

You will need to print out this PDF to get started.

Step 1: Cutting the pieces out Print the PDF and cut it into seven strips, as shown below.

Step 2: Folding Next you need to fold all of the strips down the middle.

Step 3: Cutting holes You will need the smaller pair of scissors for this bit. On each strip there is a marker to show where you cut a small hole, which will be used to hang the mobile. First you cut along the little line and then you remove the paper in the white rectangle. As the paper is folded, you can cut both sides in one go.

Step 4: Making handles This step requires very intricate work. At the end of each strip (except for the completely yellow one) you will see a marker where you need to cut the paper. Make sure you don’t cut the end off completely, but rather fold it downwards, making a handle on which to hang the next strip.

Step 5: Putting it all together Now everything is ready. Very carefully, ensuring that the paper doesn’t rip in any place, insert the handles of each strip into the holes of the next one. The strips should be ordered from bottom to top so that you see more numbers on the strips as you go up. The mobile is almost complete...

Step 6: Hanging it up you just need to something to hang it up with. For this you can either use a bit of thread or cut a very thin strip of paper.

Step 7: Finished!

And this is how it looks in action.
Now for a math question: Why does the whole mobile stay balanced?