Velocity—Not Perceived as Such: The Role of Object Mass in Velocity Estimation

Predicting object motion is critical for interacting with a dynamic world. Heavier objects tend to move more slowly than lighter ones, whether we lift them ourselves or observe larger vehicles accelerating more gradually. Here we ask whether the perceptual system internalizes everyday mass–velocity relationships described by Newton’s second law of motion. Across three experiments (N=176), we reveal a novel mass–speed illusion: heavier-looking objects are judged to move more slowly than lighter ones, despite identical physical speeds and sizes. A simple psychophysical model inspired by environmental mass–velocity statistics captures this bias. These findings overturn the assumption that mass and velocity are processed independently in human perception. Instead, our results suggest that inferred mass is woven directly into velocity perception. By internalizing environmental mass–velocity regularities, the brain bridges intuitive physics and perception, providing a unified framework for understanding motion biases and guiding adaptive behavior in a dynamic world.