A roller coaster is essentially a machine that uses gravity and inertia to manipulate potential and kinetic energy without an onboard engine. The process begins at the "lift hill," where a motor pulls the train to the highest point, building up gravitational potential energy. As the train drops, gravity pulls it downward, converting that stored energy into kinetic energy (motion). Inertia—the tendency of an object to resist changes in its state of motion—then takes over; once the train is moving, it wants to keep moving in a straight line at a constant speed. When the track curves or loops, the train’s inertia pushes the passengers against the side or into their seats, creating the sensation of "G-forces." On a vertical loop, inertia pushes you "outward" while gravity pulls you "downward"; at the top of the loop, these forces balance out to keep you in your seat even when upside down. In 2026, coaster designers use complex computer simulations to balance these forces so the ride is thrilling but safe, eventually using friction and air resistance to slowly bleed off the kinetic energy until the train stops.