This video is a classic demonstration of trailer sway and how weight distribution affects towing safety. It illustrates a fundamental principle of physics: the relationship between the center of mass and stability. The Science of Why This Happens The video shows two different scenarios on a treadmill, which simulates highway speeds: Scenario 1: Forward-Weighted (Stable) When the heavy weights (red and green) are placed at the front of the trailer (near the hitch), the trailer’s center of mass is ahead of its axle. If the trailer gets bumped, the tongue weight pushes down on the car’s rear tires, providing a “self-centering” effect that pulls the trailer back into a straight line. Scenario 2: Rear-Weighted (Unstable) When the weights are moved to the back of the trailer (behind the axle), the center of mass shifts rearward. This creates a pendulum effect. Any small movement or “flick” causes the rear weight to gain momentum, swinging the trailer side-to-side. This momentum eventually ov...