# Hockey

From the temperature of the puck to the angle of a shot on goal,
STEM helps the Anaheim Ducks score.

### More on the Science of Hockey

Learn how STEM principles power this dynamic sport.

Shooting the puck

#### Slap Shot

Slap shots allow players to use a transfer of energy to hit shots that travel at speeds over 100 mph.

A player uses a stick and his own muscles to turn potential energy into kinetic energy to execute the hardest shot in hockey. As the player winds up, bringing the stick above his shoulder, he rotates his body and transfers weight and momentum from the back skate to the front skate to the stick. Following the swing, the stick hits the ice before the puck. The stick bends, filling it with stored potential energy. As the stick releases, it hits the puck in an elastic collision and kinetic energy is transferred from the stick to the frozen puck, sending it flying.

The Gear

#### The Puck

The shape and material of a puck determine the energy it can store and how it will be affected by friction.

The ratio between the force needed to move a hockey puck horizontally over the surface of ice and the pressure between the two is a coefficient of friction. Friction opposes motion and we don’t want the puck to stick to the ice. This is why pucks are made of hard, vulcanized rubber and frozen before each game. Reducing the amount of heat in the puck reduces the amount of energy it stores, so putting pucks in the freezer reduces friction and therefore the amount of force needed to send the puck down the ice.

The Gear

#### The Stick

A hockey stick provides the net force that acts on the mass of a puck to create acceleration - Newton’s Second Law of Motion in action.

Newton’s Second Law of Motion relates to the way objects behave when existing forces are not balanced. In this case, how fast the puck accelerates depends on two factors, the net force of the stick hitting the puck and the mass of the puck. If the force of the stick hitting the puck is increased, the puck will move faster. If the mass of the puck were increased, but hit with the same force, the speed would decrease.

The Gear

#### The Ice

Water is a combination of hydrogen and oxygen molecules. Water can be a solid, liquid or gas, depending on temperature and pressure.

At 32 degrees Fahrenheit with normal atmospheric pressure, water freezes and becomes ice. But what happens to the water molecules at the very top layer of the ice, the ones that are exposed to the air and not other frozen water molecules? Those molecules can move slightly or vibrate, so the top layer of ice ends up somewhere between a solid and a liquid. This quasi-liquid layer is what makes ice slippery. But, if ice is too thick, it takes more energy to keep the surface from becoming too soft and slowing down skaters. Hockey players prefer "fast" ice, so ice rinks apply water in several layers with the total height of the ice only reaching a depth of approximately 1" thick.

The Gear

#### The Skate

To glide, skates need to have a thin layer of water between the surface of the ice and the bottom of the blade.

This quasi-liquid layer of water is actually made up of vibrating molecules. Without them, friction would make it difficult for the skate blades to glide on the ice. When a player needs to turn, start or stop quickly on this slippery top layer, skate blades have two distinct sharp edges to dig into the surface of the ice. These concave blades keep just a small portion of the blade in contact with the wet ice surface. This creates less friction and allows some NHL players to reach speeds over 20 mph.

Strategy / Players

#### Shooting Angles

The best goalies and shooters should study geometry!

Whether you are trying to score or stop a goal, it pays to understand how to play the angles. A shooter has a larger target and an easier shot if the goalie stays in the box. When a goalie moves out away from the net, she decreases the size of the area a shooter can aim at by cutting off the angles. In a split second, both offense and defense have to calculate speed and the angle of attack to either intercept or evade the other player.

Strategy / Players

#### Checking

If you want to gain possession of the puck or disrupt an opponent’s play, you may use a body check, but first you might want to study Newton’s Third Law of Motion.

According to Newton's Third Law, for every action there is an equal and opposite reaction. So what would this mean if a smaller player was checked against the boards by a larger player? It means that each player must experience the same force. When the larger player checks the smaller player, the smaller player is able to exert the same amount of force back on the larger player, slowing him down.

Strategy / Players

#### Goal Tending

When physicists use a mathematical formula to figure out the reaction time it takes to stop a puck traveling at a certain rate of speed, it is called a kinematic equation.

Kinematics is a part of mechanics that allows you to describe motion. While scientists agree that a player’s reaction time is a genetic trait, a goalie’s body can develop kinesthetic memory or muscle memory with a lot of repetitive practice of certain movements. This repetition trains the brain to respond in a certain way. Players with a good kinesthetic memory of all the various ways to stop a puck can improve their reaction time, leaving them free to think about their next move, free to focus on the puck.

Strategy / Players

#### Skating

To be a good skater, you need the slippery properties of ice, low friction between your skate blade and the ice, good technique and physical strength.

To accelerate, a hockey player leans forward and digs into the ice, pushing off with a force perpendicular to the skate blade. This places a strong force on the lower part of a player’s body as gravity pulls down a player’s center of mass, “ torqueing” him forward. If the player wasn’t accelerating, gravity would cause her to fall over. As she continues to skate, with one skate pushing and the other skate gliding, there is very little friction to slow the speed, allowing her to pick up speed.

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