The Makings of the Slapshot – Physics on Ice

By Nina Peloso

Every year before the NHL’s All-Star Game, players’ slapshots are ranked in the ‘hardest shot competition’.

With the use of the slapshot, athletes are able to propel the puck to speeds of over 100 miles per hour.

In 2020, Shea Webber took the title of ‘hardest shot’ at 106.5 mph. But the hardest shot of all-time belongs to Zdeno Chara at the A.S.G. in 2012, where he shot the puck at 108.8 mph., the fastest in recorded history.

How is All This Energy Generated?

To execute a slapshot, the player must use their body to relay energy through the stick and into the puck. This relies on the transformation of elastic energy from the stick itself, to the kinetic energy that sends the puck flying through the air.

‘Elastic energy’ is a type of potential energy that is based on the principle that ‘potential’ is stored in an object or substance as it moves into different positions. This potential emits energy/force when the object releases since it wants to revert to its original position in space. Different things happen to the force and the energy that is released. Some of it is transferred, (meaning it stays as elastic-potential energy) and some of it is transformed into different forms of energy altogether. The transfer also “loses” energy, meaning it creates some forms of energy that are not relevant to the movement. This “lost” energy is the characteristic ‘slap’ of the stick, and the bit of heat that it gives off.

In this case, the stick generates ‘elastic energy’ from flexing or bowing as the player puts pressure on it. Force travels down the stick and towards the blade as the stick amasses pent-up energy. Akin to a ‘whip’, the energy increases as it moves down the shaft as its area to occupy gets smaller and smaller. Eventually, the force hits the ice and then the puck, now as kinetic energy. As a result, the puck is able to fly through the air swiftly and neatly, barring a good follow-through of course.

From Player-to-Stick-to-Puck

To utilize these principles, the player should somewhat act as a fixed point around their stick to get the maximum flex. While their stick should act as the arm of a pendulum, pressing down into the ice throughout the motion. The tops hand pulls, and the bottom hand in pushing forward to generate the tension. As the blade hits the ice, a few inches before the puck, it bows and builds up the energy that will push the puck forward. Finally, the blade makes contact with the puck and transfers its energy, both from flexing and from being swung forward into the disc. After that, all that’s left is a clean follow-through that should help guide the puck towards the net.

The follow-through is the last step of the slapshot. Until recently, it was thought that “turning/flicking the wrist” towards the target resulted in an accurate shot. However, we now know that an evenly-horizontal path from the heel to the toe of the blade is what gets that nice, even shot that hits its target.

“Slapshot Science”

In 2002, Physics Prof. Alain Hache wrote The Physics of Hockey, which spurred many NHL teams to come to him for shooting/slapshot advice. In response, Hache came out with “Slapshot Science” in late 2015. The addition aimed to dispel some of the myths around the slapshot and answer many of the same questions he was getting from hockey players and their coaches, both amateur and pro.

1. Does the ‘Flex’ Really Matter?

The ‘flex’ of a stick is the amount of pressure it takes, in pounds, to bend the stick one-inch over a one-metre span.

There are a number of factors that go into choosing the right ‘flex’ for you. Body type, weight, position, and the length of the shaft are all considered.

Often athletes’ worries include whether they should go for a weak or stiff flex, a different curve or kick to improve their shot. Hache writes to go with comfort, but as a general rule: a lower flex is better for wrist-shots, but sacrifices accuracy.

Overall, it’s best to go with a reasonable ‘flex’ for you, based on weight and height. This mid-ground allows you to get a fair bit of flex on the shaft, which leads to energy transfer, but also to keep some accuracy and avoid breaking it as often.

2. How Can I Improve My Accuracy?

Hache asserts that accuracy, at least concerning slapshots, is largely up to chance. Even in the ‘shooting-accuracy competition’ at the annual A.S.G., where players aim to hit just four targets from 12 ft. away, players often take many shots to do so. Not to mention, slapshot-accuracy is much harder to attain than a wrist or a snap-shot.

Hache writes that there is little technique to go on beyond hitting the different quadrants of the net with body positioning and follow-through. Hence, one should focus on hitting the net with power for the greatest chance of success.