Ellipse Maker

Materials:

* square dowel, or any piece of wood with a rectangular or square cross-section, 
    10-inch length (or more)
* two nails with heads, roughly 1 inch long, not too thin
* string, preferably non-stretchy
* ruler with metric system (cm, mm) and a pen or pencil
* hammer
* scissors 

How to construct an ellipse maker:

1.  Hammer the two nails into the piece of wood, both on the same
    side.  You get to pick how far apart you want them.  Different
    separations will give you different shaped ellipses.  Three or
    four inches might be good for starters.

2.  Cut a piece of string that's at least twice as long as the
    separation between the two nails.  The longer the string, the
    bigger ellipse you'll get.  Ten to twelve inches might be good for
    your first experiment.

3.  Tie one end of the string to one nail and the other end to the
    other nail.  

    Now you are ready to draw an ellipse!

How to draw an ellipse with your ellipse maker:

1.  Place the piece of wood, nails up, on a piece of paper.  Center it
    on the paper and hold it down (it may help to have a partner do
    the holding).  The string attached to the nails will be loose.

2.  Take a pencil and use it to stretch the string out as far as it
    will go in any direction, then touch the pencil tip to the paper.  
    Keep the pencil vertical.

3.  Keeping the string stretched out as far as it can go, and the
    pencil tip on the paper, move all around one side of the wood
    until you've drawn half of your shape.  Then lift the string to
    the other side of the nails and repeat the process to draw the
    other half of the shape.  Depending on how long your stick was,
    you may need to lift it up to connect the two sides of your
    ellipse to complete the shape.

    You did it!  You have now drawn an ellipse.

Things to try:

1.  Try putting the nails farther apart or closer together and drawing
    another ellipse.  How does it compare to the first one you made?

2.  Try using a shorter or longer piece of string.  What difference
    does the string length make in the size and shape of the ellipse
    you get?

3.  Experiment with the nail separation and/or string length to see 
    what will make your ellipse look almost exactly like a circle.