Playground Ellipse Activity  Go back to lesson. Materials needed  chalk (if working on pavement) stick or lime (if working on unpaved ground) 40'-50' length of rope two stakes Procedure  1. In a smooth open area on the playground, mark two foci a few feet apart.  Place a stake in the ground at each focus, labeling one focus as the Sun.  If the area is paved, have a student at each focus holding the stake.   2. Tie the ends of the rope together and loop the rope around the stakes at the foci.   3. Pull the rope tight, as shown, and using the chalk (or making with a stick or lime, if you are on unpaved ground) draw the ellipse as shown. Notice by using the rope,  that for every point on the ellipse, the distance to one focus plus the distance to the other focus is always the same.  Have students record the measurements in order to see the pattern for themselves.  Direct them by asking questions.      4. Direct students to move around the path, slowing down as they get farther from the "Sun" and speeding up as they get closer.