Alan Kahn

Put a marble at one point along the ruler, but don't tell the students the cm position of the marble. Release the marble and let students observe that the marble moves the cup along the tabletop. Some students will likely say that the higher the marble is on the ramp, the farther the cup will move. Ask the students, "Why do you think so?" Encourage them to relate the marble and ramp to experiences they have sledding down a hill, skateboarding down a ramp, or sliding down a slide. Ask studen