Table Tennis

A flat drive cannot be landed

This is the fact the route is built on, and it is measurement rather than opinion. A ping-pong ball weighs 2.7 grams, which changes everything: air drag on it is stronger than gravity, and the sideways force from spin is nearly another gravity again.

So take one full-power stroke and divide it between pace and spin, and ask at every elevation from twenty degrees below level to forty-five above whether the ball lands —

• no spin — cannot be landed at any elevation
• a tenth of the stroke on spin — lands inside 0.25°, arriving at 10.1 metres a second
• half of it on spin — lands inside 2.75°, arriving at 7.9
• all of it on spin — lands across 10.00°, arriving at 6.7

Spin buys a forty-fold margin for error and costs a third of the pace. There is no best setting, because the bat has one speed and it has to be divided — a full brush costs 60 per cent of the pace. That is the decision the whole game is made of.

Three things you control, one input each

• Placement — where your bat is when it meets the ball. Stand to its left and it goes left. Your position matters twice: near enough to reach at all, and where within that reach decides the direction.
• Timing — when you tap. The ball is playable from the moment it bounces until it bounces again, and within 90 milliseconds of the top of that bounce is a clean stroke. Miss and the ball leaves up to 2.5 degrees off aim.
• Spin — the dial, from backspin through flat to topspin, up to 400 radians a second. It decides how much of a mistimed stroke you get away with.

The table

2.74 m by 1.525 m, with a net 15.3 cm high that overhangs the table by 15 cm on each side. Those are the real measurements. The ball is capped at 58 km/h off the bat — a real professional loop carries more than twice the spin modelled here, which would be unwatchable at this scale.

Every contact is solved for its exact moment of impact rather than tested at the end of a step. At the speed cap the ball travels 67 mm in one logical step and is 40 mm across, so a test run afterwards could miss a bounce altogether — and a ball that misses the table is a ball underneath it. The net is treated as a plane with a hole above it rather than a solid box, so a ball that clears the cord by a millimetre goes over rather than bouncing off thin air.

The modes

• Vs bot — a full game to 11, win by two, against the house
• Two players — two people at one screen, taking the ends in turn
• Practice rally — no score, just how long a rally you can keep going
• Target challenge — land the ball inside the rings; they move every time you clear them

Zerdly’s chosen rules

• Singles, first to 11, win by two. Service changes every 2 points, and every single point once both players reach 10.
• A serve bounces in the server’s own half first and then the receiver’s. A serve that clips the net is a let and is replayed; a net cord during a rally is simply part of play.
• The expedite rule: a rally that runs past 20 seconds goes to the receiver. Without it a long rally has no end — a test match sat at nil-all through 41 rallies and 743 strokes, every one of them replayed.
• Simplified: no doubles service box, no toss requirement, and your bat follows the ball in depth so you are placing and timing rather than steering in three dimensions through a touchscreen.

The opponent, and how it is beaten

It moves at the same 4 metres a second you do, reaches the same 33.0 centimetres past itself, and plays every stroke through the same physics — so a ball it could not land, it does not land. What the levels change is reaction, timing and placement, and all three are things a person can also be better at. Easy reacts in 0.36 seconds and plays close to the middle; Hard reacts in 0.12 and uses the corners.

It is beaten the way a person is beaten: by putting the ball where they are not, early enough that they cannot get there, and by making them play a ball they have to reach for.

Local play

Everything runs in this browser: the table, the physics, the opponent 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. Two-player is two people at one screen, not anything over a network.

Questions

Why does my hardest shot always go out?

Because a flat one cannot be landed at all. A ping-pong ball weighs 2.7 grams, so air drag on it is stronger than gravity — at 10 metres a second it slows the ball at about 11.2 metres per second squared. Aim a full-power flat drive low and it catches the net; aim it higher and it lands past the far edge; and measured across every elevation from twenty degrees below level to forty-five above, there is nothing in between that lands on the table. The gap is closed by spin, not by aiming better.

So what does spin actually do?

Two things, and both are big. In the air it presses a topspun ball downwards with nearly the force of another gravity, so the ball comes down inside the table from a trajectory that would otherwise be long. Off the bounce it grips the cloth and throws the ball forward, which is why a looped ball kicks at you. Measured on one full-power stroke: with a tenth of it spent on spin the ball lands inside a quarter of a degree of elevation; with all of it on spin the window is ten degrees wide. That is forty times the margin for error.

Then why not use maximum spin every time?

Because the bat has one speed and it has to be divided. A full brush costs 60 per cent of the pace, so the safest shot is also the slowest: the same stroke arrives at about 10 metres a second with a little spin and 6.7 with a lot. The fastest ball that can be landed at all runs from about 55 km/h flat to 86 with everything on spin. There is no best setting — that is the decision the game is made of.

How do I control where it goes?

With where your bat is when it meets the ball. Stand to the ball's left and it goes left, because that is what an angled bat does. So your position matters twice: near enough to reach the ball at all, and where within that reach decides the direction. Reaching a wide ball at full stretch leaves you no angle and you can only push it back down the middle — which is exactly the penalty a real player pays for being pulled out of position.

What is the timing for?

The ball is playable from the moment it bounces on your side until it bounces again, and where in that window you hit it decides how clean the stroke is. Within 90 milliseconds of the top of the bounce is perfect; tap early or late and the ball leaves up to 2.5 degrees off where you aimed. Whether that matters depends entirely on your spin — a heavily spun ball still lands with the worst timing in the game, and a flat one almost never does.

What are the rules used here?

Singles, first to 11, win by two. Service changes every 2 points and every single point once both players reach 10. A serve must bounce in the server's own half and then the receiver's; a serve that clips the net is a let and is replayed, while a net cord during a rally is simply play. A rally that runs past 20 seconds goes to the receiver under the expedite rule.

Why is there an expedite rule?

Because without one a long rally has no end. Two players who can both reach everything will rally indefinitely, and a test match sat at nil-all through 41 rallies and 743 strokes before the rule existed — every one of them replayed. It is a real rule in the sport and it is here for the real reason.

What has been simplified?

There is no doubles service box, no two-metre toss requirement, and your bat follows the ball in depth automatically. That last one is deliberate: it means you are placing and timing the stroke rather than also steering in three dimensions through a touchscreen, which is not a game. Everything else — the table, the net, the bounce, the drag and the spin — is the real thing.

Does the opponent cheat?

No, and it structurally cannot. It moves at the same 4 metres a second you do, reaches the same 33.0 centimetres, and plays through the same physics — so a shot it cannot land, it does not land. What changes between levels is reaction, timing and placement, all of them things a person can also be better at. Easy reacts in 0.36 seconds and plays close to the middle; Hard reacts in 0.12 and uses the corners.

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 bounded too, so a tab you left for a minute does not come back and play a minute of table tennis in one frame.

Does any of this run on a server?

No. The table, the physics, the opponent 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

• Air Hockey — the other route where a player guards a line rather than a goal
• Bowling — where a straight ball cannot strike, for much the same reason spin matters here
• Pool & Billiards — the angle off a cushion as the whole shot
• Darts — the nearest thing here to pure placement under pressure
• Basketball Shootout — where a flat shot cannot go in at all — the same shape of fact