Ellipse Definition: Lesson for Kids

Instructor: Kathleen Laib

I have been a teacher for 10 years with eight of those years teaching 4th grade. I have a master's of Ed and an ELL Endorsement.

In this lesson we'll look at the definition of an ellipse. We'll also look at the mathematical characteristics of an ellipse. At the end of this lesson, you'll find an activity to help you create your own ellipse.

Isn't It Just an Oval?

No, it's not that simple. All ellipses are ovals, but not all ovals are ellipses. When you move past just recognizing shapes and into understanding the mathematical characteristics of an ellipse, you'll find that it is actually a pretty complicated and interesting figure.

To create an ellipse, you'll start with two spots in space. Each one is called a focus, but together they are called foci. These two foci will not move.


Next, pick a third point a little away from the foci. To help draw the ellipse, keep in mind the triangle that is formed when you connect the two foci and the third point.

Now, replace the third point with a pencil and imagine a string forming the triangle around all three points in space, the two foci and the pencil that marks the third point. Keep the string pulled tight, but move the pencil around the outside of the two foci. The pencil will be forced to travel a path within the string. That path will form an ellipse.

Using a string to make an ellipse
Making an ellipse

The size of the string does not change its length as the pencil moves through space around the foci. This leads to the definition of an ellipse. An ellipse is formed when the sum of --meaning when you add together-- the distance between the two foci and any point along the curve of the ellipse remains equal, no matter where that point is on the ellipse.

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