What’s small and round, made of vulcanized rubber, and kept in the freezer before you play with it? That’s right—a grenade! Or at least that’s what NHL players call a loose puck as it bounces on the ice. This installment of the Science of NHL Hockey, produced by NBC Learn in partnership with NSF and NSTA, explores the crazy collisions of pucks with practically everything in the rink.

Why are pucks frozen? For the same reason the goalie is padded from head to toe—to reduce elasticity and stifle the puck’s reaction during a collision. The less the puck deforms, the less of the pucks’ energy of motion converted to some other form of energy slowing it down, and the colder it is, the faster it’ll scream across the ice.

If your students haven’t yet watched Newton’s Three Laws of Motion, consider showing that one first to refresh students’ memories of why objects move as they do. Then focus in on how the changing force of the stick can cause the puck to gently glide across the ice or shoot towards the net at speeds of 90 mph (about 150 kph) or more!

—Judy Elgin Jensen

Image courtesy of Kim Faires

Video: In “Force, Impulse & Collisions,” NSF experts explain the motion of the puck as it careens around the rink.

Middle school lesson: In this lesson, students will relate impulse and momentum and explore elastic and inelastic collisions.

High school lesson: In this lesson, students will explore impulses and investigate momentum and energy transfer in elastic and inelastic collisions.

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