When you spin a fully expanded Hoberman Sphere, it rotates slowly. But if you collapse it mid-spin, the rotation speeds up dramatically. First we need to know that momentum measures how difficult it is to stop a moving object and it depends on the object's mass and velocity: ▪︎ Linear momentum refers to straight line motion (a tennis ball is easier to stop than a bowling ball). ▪︎ Angular momentum applies to spinning objects and depends on mass and angular velocity (a coin flip is easier to stop