Mass, Volume & Density

NHL fans might be surprised to learn that the ice surface at a hockey rink is only about one inch thick. Scientists and ice technicians explain the science and math that goes into building and maintaining this surface through the long NHL season. "Science of NHL Hockey" is a 10-part video series produced in partnership with the National Science Foundation and the National Hockey League.

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LESTER HOLT, reporting: They're the superstars of the National Hockey League. Stamkos, Ovechkin, Crosby, and many other players who perform amazing feats every time they step on the ice.

But almost as important to the game of hockey are people like Nick Kryshak, ice technician for the New Jersey Devils.

NICK KRYSHAK (Ice Technician, New Jersey Devils): When you have stars like that skating on your ice, you know, nobody knows who I am normally, well, I'm the guy who does it.

HOLT: NHL ice technicians do much more than just drive the Zamboni between periods. They also apply science and mathematics to help build and maintain an ice rink through the long NHL season. It all starts with water.

Dr. JIM GATES (University of Maryland): Hockey takes advantage of one of the most interesting substances in the universe, mainly water. Perhaps the most interesting property of water is that we can see three states of its existence within a relatively narrow temperature range.

HOLT: Between zero and 100-degrees Celsius, or 32 and 212-degrees Fahrenheit, water is in its liquid state. Above that, water transforms into a gas or water vapor called steam. Below that, water freezes into a solid block of ice.

GATES: If you put enough other substances like, say, salt into the water, you can actually change the temperature at which it turns to ice and ice rinks take advantage of this change.

HOLT: At the home of the New Jersey Devils, a saltwater solution, or brine, is pumped through a series of pipes underneath the concrete floor to cool it. This enables the water in the pipe to remain a liquid, while still being cold enough to freeze the ice above.

JIM CIMA (Senior V.P., Arena Operations, New Jersey Devils): Initially we have to get this temperature down on the brine, to about six degrees in order to get the temperature down and to make ice.

HOLT: The ice-making process begins by building a layer, just a 32-nd of an inch thick, directly onto the concrete floor. This layer of ice is painted white, then more layers of ice are added and lines and logos are drawn. The entire ice-making process takes as long as 48-hours but once it's built, it stays intact throughout the season.

PEKKA RINNE (Goaltender, Nashville Predators): It's unbelievable how they can do it at the rink, you know, having a basketball game in the afternoon and having a hockey game that night.

HOLT: The official size of an NHL hockey rink is 200-feet long by 85-feet wide. To form this massive ice sheet takes about 10,600 gallons of water, or about 40-thousand liters. Incredibly, the ice itself is only about an inch thick.

Dr. IRENE FONSECA (Carnegie Mellon University): When you produce ice by layering water on the rink you have to keep in mind that when it solidifies it has more volume than if it was just water. So it expands.

HOLT: Volume is the amount of space something occupies in terms of its length, width and height. When water freezes, it expands. This is why pipes sometimes break in the wintertime. The formula for the volume of a rectangular solid is length-times-width-times-height. Since the ice sheet is very close to that of a rectangular solid, and since we know all these variables, it's easy to calculate the volume of the ice sheet: 43.6 cubic meters. To maintain this volume, Cima and his team closely monitor the surface temperature and thickness of the ice.

CIMA: This actually measures the thickness of the ice. The purpose of that is just to check that we are in fact achieving the thicknesses that we want to achieve throughout. And for the ice technician who runs the Zamboni, it tells him where he's got to drop more water.

HOLT: The Zamboni is an important part of maintaining the ice surface. Its secret lies in the conditioner, a rectangular unit attached to the rear of the vehicle. Inside, a cutter shaves a thin layer of ice, and a sprinkler spreads a fresh layer of water, which is heated and purified to remove air and other contaminants dissolved in the water.

KRYSHAK: The more solids you have, the dirtier your ice is. With the purification system that we have, it takes all of that stuff out so that you have a tight, hard sheet which is exactly what you want for hockey.

HOLT: Another interesting fact about ice is that it's actually less dense than water. This is why ice cubes float in a drink.

FONSECA: Density is how much mass exists in a given volume, so it's a quotient, it's a fraction, it’s mass over volume.

HOLT: Mass is the measure of how much of something there is, literally the amount of particles that make up an object. But regardless of the sample size, density is always constant. The density of water is 1,000 kilograms per cubic meter, while the density of ice is less, 917-kilograms per meter. Knowing the formula, mass-equals-density-times-volume, it's possible to calculate the mass of ice in a hockey rink: 40,000 kilograms. If that number looks familiar, that's because it's the same as the volume of water it takes to make the ice sheet. The more densely packed this massive ice sheet is, the harder and faster it will be for players to skate on. In the NHL, players refer to this as “fast” and “slow” ice.

ERIK JOHNSON (Defenseman, Colorado Avalanche): I always prefer to play on fast ice, you know, slow ice is when it's really soft and there's a lot of water and gets a lot of snow buildup and you are really digging into the ice a little bit more. And fast ice is a good hard sheet.

HOLT: With science and math as their guide, NHL ice technicians turn their craft into an art form. Creating the smooth hard surface upon which NHL stars perform their magic.

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