Air Hockey

A direct shot does not beat a defender

This is the fact the route is built on, and it is arithmetic rather than opinion. A mallet is 3.8 inches across and the goal mouth is 10.0, so a mallet parked in the middle of its own goal covers about 38 per cent of it. It cannot guard the goal. What it can do is guard the LINE the puck is travelling on — and a direct shot tells it that line early.

Measured: fired from one spot at every angle at 12 metres a second, against a defender sitting on the line between the puck and the middle of its own goal —

• direct shots that scored — none of them
• shots that came off a rail first — as many as against an empty goal

So the skill is not pace. It is changing where the puck is coming from, after the other player has committed.

Why a rail bounce is still dangerous

The puck sits on a cushion of air, so it barely slows down: the deceleration here is 0.25 metres per second squared, and a rail returns 88 per cent of the speed. A hard shot can bounce a dozen times before it is a slow puck. That is the character of the game and it is the number most likely to ruin it — put real friction in and the table becomes shuffleboard, where nothing rebounds and defending is free.

The table is 84.0 by 42.0 inches, twice as long as it is wide. That ratio is what makes a bank shot come back toward the goal from the side rather than running parallel to it.

The puck cannot leave the table

At its cap of 65 km/h the puck travels 75 mm in one logical step and is 83 mm across, so a collision test run at the end of a step could miss a rail the puck had already crossed. Instead every contact is solved for its exact moment of impact and the step stops there — including the goal posts, which are tested as their own separate case because a swept test against a flat rail is blind at the rail’s ends.

That is checked by exhaustion rather than by sampling: 576 shots, every whole degree, at the speed limit, from the middle of the table and from the three worst places to start — hard against a rail, wedged in a corner, and sitting in the goal mouth. None of them escapes. A puck can pass through 6.8 inches of the 10.0-inch mouth, because the posts are solid and a puck is 3.3 inches wide.

The modes

• Vs Bot — First to five against the house. It reads where the puck will cross its line and gets there — so beat it with a bank shot rather than pace.
• Same-device 2 Player — Two people, one screen, one finger each. Both mallets move at once; neither can cross the centre line.
• First to 7 — A longer match against the house, which is a different game — over seven goals a bank shot you have already used stops working.
• Time Attack — Ninety seconds, an empty net and no opponent. How many can you put away, and how few come back at you.

The house, and how it is beaten

It works out where the puck will cross its own line — through the rails — by running the same physics your puck runs, so its prediction agrees with what actually happens to within a couple of millimetres. It never moves faster than its level allows, it cannot cross the centre line, and it never jumps: a mallet that teleported would be a mallet that could not be beaten.

What the levels change is how fresh its information is. Easy acts on what it saw 0.44 seconds ago and re-reads the table every 0.4; Hard is 0.05 and 0.05. So it is beaten the way a person is beaten — by changing the puck’s direction inside the gap between its decisions. Your own mallet is capped at 22 km/h, which is faster than any of them.

Zerdly’s chosen rules

• A mallet stays in its own half, edge and all. A goal counts only through the opening. The puck is served in front of whoever conceded.
• The seven-second rule: a puck at rest in your half is yours to play for 7 seconds, after which it goes to the other end. It is a real tournament rule, and without it a player who ignored the puck would stop the game — the other mallet cannot legally reach it.
• Two-player games are not scored, because two people at one screen is not a result either of them owns.

Local play

Everything runs in this browser: the table, the physics, the house player and every sound. No sign-in, no leaderboard, no account. Settings and bests live in local storage under this route’s own keys, and clearing this game’s data leaves every other Zerdly tool alone. The two-player mode is two people at one screen, not anything over a network.

Questions

Why can I not score straight at the goal?

Because a defender only has to cover the line the puck is on, and yours is easy to read. A mallet is 3.8 inches across and the goal is 10.0, so it covers about 38 per cent of the mouth — but that is enough when it knows where the puck is going. Measured against this table, a defender sitting on the puck-to-goal line stopped every single direct shot from a fixed spot, and almost none of the shots that came off a rail first.

So how do I score?

Play it off a side rail. A banked puck arrives from a direction the defender is not covering, and it changes direction late — after they have committed. The table is twice as long as it is wide, which is exactly the geometry that makes a rail bounce come back at the goal from the side rather than running parallel to it.

Why does the puck never seem to slow down?

Because it is sitting on a cushion of air. The deceleration here is 0.25 metres per second squared — about a fortieth of what a puck on a table would feel — and a rail gives back 88 per cent of the speed. That is the whole character of the game: a puck you mishit comes straight back at you, and a rally can go on for a dozen rail bounces.

How fast can the puck go?

Up to 65 km/h, and that cap is doing two jobs. It keeps the game playable, and it stops the puck from being able to pass through a rail between one logical step and the next — at that speed it travels 75 mm a step, just under its own width. Every contact is also solved for its exact moment of impact rather than checked afterwards, so the puck cannot leave the table at all. That is tested across 576 shots fired at every angle from the four worst places on the surface.

Can my mallet cross the centre line?

No, and it is the mallet's EDGE that is stopped rather than its centre — a mallet centred on the line would be half-way into the other half. The same function enforces it for you and for the house, so there is no way for one of you to have a slightly different rule.

How does two players on one screen work?

Each finger is tracked separately, and it is assigned to whichever half it first touched down in. It keeps that half until it lifts, so player one's thumb cannot steal player two's mallet by wandering over the line. The play surface also refuses page gestures while you are on it, so a drag moves a mallet rather than scrolling the page.

Does the house cheat?

No, and it structurally cannot: it works out where the puck will cross its own line by running the same physics your puck runs, so its prediction is exactly as good as the rules are. What the levels change is how fresh its information is — Easy acts on what it saw 0.44s ago and re-reads the table every 0.4s, Medium acts on what it saw 0.2s ago and re-reads the table every 0.18s, Hard acts on what it saw 0.05s ago and re-reads the table every 0.05s. It is beaten the way a person is beaten: by changing the puck's direction inside the gap between its decisions.

What is the seven-second rule?

If the puck comes to rest in your half you have 7 seconds to play it, after which it is served to the other end. It is a real tournament rule and it is here for a real reason: the puck is served in front of whoever conceded, and the other mallet cannot legally reach it — so a player who ignores it would stop the game entirely. A test that played a 300-second match found exactly that, with the score stuck at 0–0.

What are the four modes?

Vs Bot: First to five against the house. It reads where the puck will cross its line and gets there — so beat it with a bank shot rather than pace. Same-device 2 Player: Two people, one screen, one finger each. Both mallets move at once; neither can cross the centre line. First to 7: A longer match against the house, which is a different game — over seven goals a bank shot you have already used stops working. Time Attack: Ninety seconds, an empty net and no opponent. How many can you put away, and how few come back at you.

Does the frame rate change the game?

No. The simulation advances on fixed logical steps of a 240th of a second, accumulated from real time, so a 30 Hz screen and a 144 Hz screen run the same number of steps a second. The catch-up is also bounded, so a tab you left for a minute does not come back and play a minute of hockey in one frame.

Does any of this run on a server?

No. The table, the physics, the house player and every sound run in this browser. There is no sign-in, no leaderboard and no account. Settings and bests are kept in local storage under this route's own keys, and clearing this game's data leaves every other Zerdly tool alone.

Related interactives

• Pool & Billiards — the other route where the angle off a cushion is the whole shot
• Hover Racer — the spec's suggested link — a boost worth spending in different places on different courses
• Endless Highway Racer — a racer that is not a race, and the nearest thing here to a reaction test
• Micro Kart Sprint — drifting measured as worth 2.6 per cent, which is the sort of margin this game trades in
• Boat Racer — where the current costs you position rather than time