Puck & Ice Friction Physics

The puck as a physics object

A regulation puck is vulcanised rubber, 76.2 mm (3 in) in diameter, 25.4 mm (1 in) thick and roughly 170 g (6 oz). Game pucks are chilled before use because cold rubber is harder and less elastic: it bounces less, rolls onto its edge less often and slides with a more consistent contact patch. In the Questswatchpatch engine the puck is modelled as a rigid disc of mass m = 0.17 kg with its centre sitting 12.7 mm above the ice while it slides.

Two forces work against a moving puck: kinetic friction whenever it touches the ice, and aerodynamic drag at all times. Gravity pulls elevated shots back down, and the boards and goal frame redirect it. Everything else in a shot, from the goaltender's chances to the telemetry you see after release, is downstream of these forces.

Kinetic friction on ice

Sliding friction follows the classic Coulomb model. The friction force is proportional to the normal force, which for a puck lying flat is simply its weight:

F_f = μk · m · g
a_f = F_f / m = μk · g

Because mass cancels, deceleration depends only on the coefficient of kinetic friction, μk. Ice is exceptional here. A thin, quasi-liquid layer at the surface, reinforced by frictional heating at the contact points, lets rubber glide with coefficients far below everyday materials. Hockey ice is typically held around −5 °C to −3 °C; harder, colder ice is faster for pucks, while warmer, softer ice suits figure skating.

The simulator offers three presets, each representing a realistic moment in a game:

• Fresh resurface, μk = 0.004: a newly flooded sheet, smooth and glassy.
• Mid-period, μk = 0.006: light snow build-up and skate grooves.
• Chopped ice, μk = 0.011: late in a period, heavy snow and ruts that grab the puck.

At μk = 0.006 the friction deceleration is 0.006 × 9.81 ≈ 0.059 m/s². A slapshot travelling at 30 m/s along the ice loses only about 0.06 m/s every second. Over a 10 m shot that lasts a third of a second, friction removes roughly 0.02 m/s. That is why the Ice Friction Loss readout for a hard shot is tiny, and why it becomes significant only for slow passes, rims and dump-ins.

Stopping distance and why air matters more

Using energy conservation, friction alone would stop a sliding puck over a distance of:

d_stop = v² / (2 · μk · g)

For a 12 m/s pass on fresh ice this gives more than a kilometre, which obviously never happens. The missing ingredient is drag. Aerodynamic resistance scales with the square of speed:

F_d = ½ · ρ · Cd · A · v²
k   = ρ · Cd · A / (2m) ≈ 0.0035 m⁻¹
v(d) = v0 · e^(−k·d)

With air density ρ ≈ 1.2 kg/m³, a drag coefficient near 0.5 and an edge-on frontal area of about 0.0019 m², the engine's drag constant is k ≈ 0.0035 per metre. Over 10 m, drag removes about 3.4% of a shot's speed: at 45 m/s that is roughly 1.5 m/s, around seventy times more than friction. For elevated shots the puck never touches the ice at all, so drag and gravity are the only decelerating forces until it strikes the net, the goaltender or the glass.

Kinetic energy transfer from stick to puck

The energy carried by the puck is:

KE = ½ · m · v²
KE(45 m/s) = ½ · 0.17 · 45² ≈ 172 J

A slapshot produces that energy in two stages. First, the player strikes the ice just behind the puck, bending the shaft and storing elastic energy, approximated by E = ½ · k_s · x² for shaft stiffness k_s and deflection x. Second, as the blade drives through the puck, the shaft recoils and releases that energy into the blade velocity at the moment of contact. The collision itself is brief, on the order of milliseconds, and can be approximated by an impulse model:

v_puck ≈ (1 + e) · M_eff / (M_eff + m) · v_blade

Here M_eff is the effective mass of the blade and lower shaft and e is the coefficient of restitution between blade and puck. Because M_eff is several times larger than the puck, a well-timed release can send the puck noticeably faster than the blade itself was moving.

How the simulator converts power to velocity

The engine abstracts the stick into a single charge value P between 0 and 1, built by holding the input for up to 1.1 seconds. Release speed is linear in P:

v0 = 17 + 28 · P    (m/s)
σ_scatter = 0.03 + 0.10 · P² + 0.30 · overwind    (m)

The top of the range, 45 m/s or about 162 km/h, reflects an elite slapshot. The quadratic scatter term represents the loss of control that comes with maximum effort, and the overwind term punishes holding the stick loaded for more than 1.6 seconds. After each shot, the telemetry panel reports the friction work as a percentage of initial kinetic energy, letting you compare ice presets directly.