We all know the story: The clock strikes midnight and Cinderella, facing an imminent wardrobe malfunction, flees the royal ball, leaving behind a single glass slipper. The prince travels the kingdom until he finds the woman who fits the shoe, and the two are married.

But, Cinderella’s chance to live happily ever after could just as easily have been shattered, say physics students who used stress calculations to assess the durability of her glass footwear. 

“When standing, the force acting downward is assumed to be evenly shared between her feet,” they explain. But, if she’s walking or running, that downward force is pushing entirely on one foot at a time. 

The result? Cinderella’s glass slippers would have broken (as would her heart)