Students explore the physics exploited by engineers in designing today's roller coasters, including potential and kinetic energy, friction and gravity. First, they learn that all true roller coasters are completely driven by the force of gravity and that the conversion between potential and kinetic energy is essential to all roller coasters. Second, they consider the role of friction in slowing down cars in roller coasters. Finally, they examine the acceleration of roller coaster cars as they travel around the track. During the associated activity, students design, build and analyze model roller coasters they make using foam tubing and marbles (as the cars).