of all planets, asteroids, and most comets have in common? 3. Controlling Variables What is the independent variable for the ellipses you will draw? 4. Controlling Variables What are the dependent variables for the ellipses you will draw? 5. Designing Experiments What purpose do the two pushpins serve in this investigation? Materials (per pair of students) 3 sheets of paper heavy corrugated cardboard (~50 cm x 60 cm) 2 pushpins metric ruler string, 30 cm long 5 colored pencils cellophane tape calculator Ps