Hockey is a complicated sport: 12 players battle on frozen ice, navigating the game on thin metal blades beneath their skates. Players try to hit a frozen disk-shaped puck into the goal, and the team with the most points after three periods wins.
While the physics department may seem worlds away from Lynah Rink, this icy sport that would be impossible without the fundamental laws of the physical sciences.
The first and, arguably, the most important component of hockey is the puck. Hockey pucks are made of vulcanized rubber and are frozen between games. “If you want the puck to stay on the ice and not bounce all over the ice, you [need to] freeze it to reduce the elasticity,” explained Samuel Bader grad, a Ph.D. candidate studying applied engineering and physics.
Another crucial aspect of hockey is the player’s ability to effortlessly glide on the ice with special hockey skates. “The skates in hockey are actually quite an interesting shape: The tip is really two points separated by a slight groove,” Bader said.
Specific conditions and the physical properties of ice further impact players’ abilities to skate smoothly. As the compression from the narrow skate blade helps melt ice, skaters are able to move more effortlessly.
“The low-friction interface critical for skating can be attributed to the thin-layer of quasi-liquid water between a player’s blade and the solid-ice beneath,” Bader said.
“Less work is required to break dangling bonds at the liquid water surface when speeding up, in contrast with the person with sneakers walking on concrete,” explained Nima Leclerc ’20, a student majoring in Applied Engineering Physics in the College of Engineering.
But despite the benefits and speed brought by a smooth surface, sometimes friction is also critical in helping players accelerate and decelerate quickly and move laterally. The process of building speed involves the skater repeatedly pushing off with blades angled away from the direction of motion, Bader said.
“Ice inherently makes a low friction interface between chrome-coated steel and itself, given that its coefficient of kinetic friction is over 100 times smaller than the contact between our sneakers and the concrete surfaces we walk on,” Leclerc said.
Alternatively, hockey players often dig their skates into the ice in order to slow down or decelerate “to impose a lateral force opposite to the direction of friction,” according to Leclerc.
“It is the physical differences between ice and normal surfaces that allow players to enable lateral motion to glide, rather than a transverse motion to walk on a surface,” Leclerc said.
Furthermore, the type of the blade on the hockey skates determines players’ mobilities. “Skates with a deeper groove dig into the ice further for more grip, while skates with a flatter groove glide more smoothly on the ice surface,” Bader said.
In hockey — or any sport that requires skating — it is essential that players balance on the ice while moving quickly. Finding the right balance, therefore, is essential because the act of skating is essentially a clever manipulation of friction. The design of the hockey stick makes it possible for players to hit the puck and score goals; optimal hockey sticks are designed to accelerate the puck from the small force generated by the player’s swing.
“Holding force constant, one desires that the lower region of the stick be long enough to yield the maximum torque, as torque is proportional to the length of the lever arm being rotated,” Leclerc said.
“Every sport worth playing carves out its own niche in the interplay of physics, strategy and the ultimate limitations of the human body,” Leclerc said.