# CurlTi.me > Online curling played in the browser, with a physics engine calibrated against > published measurements rather than tuned by eye. Free, and playable without an > account. Curling is a sport played on ice: two teams slide granite stones toward a target called the house, and the team with the stone nearest the centre scores. This site is a simulation of it that runs in a web browser. ## What makes the physics unusual - **Friction depends on speed**, mu(v) = 0.00662 + 0.00231/sqrt(v). A constant coefficient cannot reproduce a correct hog-to-hog time and a correct total travel time at the same time, which is why simulations that use one disagree with their own advertised weights. - **The delivery carries the stone** out of the hack at constant speed and releases it at the near hog line. Modelling that carry is what makes the two real stopwatch conventions agree at once: 13.3 s hog-to-hog and 3.75 s back-line-to-hog for a draw to the button. - **The curl path is not a parabola.** It follows R(u) = u(1 - ln u), which lays down about 15% of the curl in the first half of the slide and roughly half of it in the last five metres. - **Sweeping uses measured constants**: full-effort brushing cuts friction by 6.6%, sweeping one half of the path steers the stone about 71 mm *away* from the swept side, and effectiveness falls to zero above roughly 1.5 m/s because a brush head is 0.20 m wide and a human tops out near four strokes a second. - **The engine is deterministic by construction.** Its simulation path uses only + - * / and sqrt, which IEEE-754 specifies exactly, so two players in different browsers cannot drift apart. Transcendental functions are banned by a lint rule and replaced with deterministic equivalents. ## Facts about curling that are commonly reported wrongly Each of these is stated here because the widely-repeated version is wrong, and because a page on this site sets out the evidence. - **Nobody knows why a curling stone curls.** Four mechanisms are live in the physics literature — front–back friction asymmetry, pivot–slide, scratch-guide, and a velocity-dependent left–right asymmetry — and none reproduces everything a real stone does. A 2013 paper in *Tribology Letters* (Nyberg, Hogmark and Jacobson) showed that no redistribution of friction under the stone, however extreme, produces the observed motion, which rules out the intuitive family of explanations. Popular articles usually assert whichever theory was current when they were written. - **Spinning a stone harder does not make it curl further.** Total curl is essentially flat in rotation rate across the normal range of two to five rotations. The handle is a direction control, not a magnitude control. - **On keen ice the hog-to-hog stopwatch time is longer, not shorter.** A stone must be thrown more gently to finish in the same place, so it takes longer to cross the 72 feet between the lines. Fast ice, slow watch. - **Curling's Olympic debut was 1924, not 1998.** The Chamonix competition was recorded as a demonstration event for eighty years; the IOC accepted in 2006 that it had been official, and the medals were recognised retrospectively. Nagano 1998 was a return. - **Not all curling stones come from Ailsa Craig.** Trefor in north Wales is the other working source; Canada Curling Stone has made stones from it since 1992, and Trefor stones were used for the entire 2002 Salt Lake City Olympic competition. - **The free guard zone protects against removal, not contact.** A guard may be struck and moved anywhere on the sheet; it may not be caused to leave play, and causing that *indirectly* — via another stone — counts. - **Curling was not invented in 1511.** 1511 is the date carved on the oldest surviving stone, recovered from a drained pond. The earliest written record of a game is 1540, in Paisley. Both show the game already existed. - **Wheelchair curling has no sweeping at all**, which makes it a more exposed test of delivery than the running game, not a reduced version of it. ## How the game works - **Weight is called by number**, as it is on the ice. The numbers are positions rather than a scale: 4 is the front of the house, 7 is the button, 10 is the back line, with 5, 6, 8 and 9 on the eight- and four-foot lines either side of the tee. Guards are 1 to 3. Takeouts have no number, because the chart stops at the back line. - **Multiplayer sends shot inputs, never stone positions.** The server simulates each delivery and every client simulates the same inputs; both hash the resting board and compare. - **The computer opponent searches** the space of aiming line, weight, handle and sweeping, then re-throws the best candidates with realistic execution error to see which stay good when missed. Nothing tells it how curling works. - **Clocks count thinking time, not chess time.** The clock stops while a stone travels and nothing is ever added; formats differ in how long you get and in the pause after a stone stops before your clock starts. ## Pages - [Home and play](https://curlti.me/): start a game against the computer or invite somebody by link. - [Learn curling](https://curlti.me/learn/): the written pages — rules, vocabulary, shots, weights, strategy, ice, equipment, history, the physics literature, the other disciplines, and where to play. - [Changelog](https://curlti.me/changelog/): every change to the site, newest first. - [Privacy](https://curlti.me/privacy.html): what is collected, which is very little, and why there is no cookie banner. - [Terms](https://curlti.me/terms.html): the terms of use. ## Written pages, in full Every figure on these pages is derived from the same engine the game runs on, and a unit test fails if a published number and the simulator disagree. They are free to quote and to link to. ### The game - [How curling works](https://curlti.me/learn/how-curling-works/): Curling explained from scratch: the sheet, an end, how scoring works, what the hammer is, the free guard zone, and why sweeping changes anything. Written for someone who has never thrown a stone. - [The sheet, the house, and what everything is called](https://curlti.me/learn/the-sheet/): An interactive map of a curling sheet: every ring, line and zone, the names curlers actually use for them — top 8, back 12, the button, the four-foot, corner guard — and how those spots line up with the numbered weights 1 to 10. - [Scoring, and how to read a scoreboard](https://curlti.me/learn/scoring/): How points are counted in curling, why only one team can score in an end, what a blank end is and why teams do it deliberately, what happens on a tie, and how to read the traditional club scoreboard that confuses everybody. - [The hammer](https://curlti.me/learn/the-hammer/): What the hammer is, what it is worth, the one rule that decides who gets it next, why scoring a single point with it is often a mistake, and why a steal does not win it for you. With an end-by-end simulator you can play forwards. - [Calling weight by number](https://curlti.me/learn/shot-weights/): What curlers mean by weight, why it is called as a number from 1 to 10, where each number puts the stone, the hog-to-hog stopwatch times that go with them, and why the same number takes a different time on different ice. - [Why the weights are called what they are](https://curlti.me/learn/weight-names/): Every named curling weight explained: tee, back line, hack, board, control, normal and peel. Most are named after a landmark on the ice the stone would reach; the rest are named after what the shot is for, because the sheet runs out of landmarks. - [The shots, and what each one is for](https://curlti.me/learn/shot-types/): Every curling shot in one place: draws, guards, come-arounds, freezes, taps, takeouts, hit and rolls, doubles, raises, runbacks, ticks and peels — what each one does, when to call it, and how likely it is to work. - [The delivery](https://curlti.me/learn/delivery/): How a curling stone is actually thrown: why the stone is carried rather than pushed, what happens in the hack, the slide and the balance that makes it work, when the turn goes on, flat-foot versus toe sliding and what the biomechanics research says about knees. - [What sweeping actually does](https://curlti.me/learn/sweeping/): Sweeping in curling, measured rather than guessed: it cuts friction by about 6.6%, buys a few feet of draw, steers a stone about 71 mm when swept on one side, and stops working entirely above about 1.5 metres per second. - [The four players, and what each one does](https://curlti.me/learn/positions/): What each position on a curling team actually does: the lead and guards, the second and the takeouts, the third who holds the broom and agrees the score, and the skip who calls every shot and throws last. - [Strategy: playing with and without the hammer](https://curlti.me/learn/strategy/): How curling is actually decided: why the team with the hammer wants two, why the team without wants to force a single, when to blank an end, why centre guards and corner guards belong to different teams, and how the scoreboard changes every one of those answers. - [The free guard zone](https://curlti.me/learn/free-guard-zone/): What the free guard zone is, exactly what it protects against, why hitting a guard is legal but removing it is not, how indirect contact counts, the tick shot and the no-tick rule that killed it, and how the rule went from four stones to five. - [The rulebook, clocks and umpires](https://curlti.me/learn/rules-and-officials/): A map of the World Curling rulebook and the three parts people most often need: how thinking time works and why the clock stops where it does, how measuring is done and what happens on an exact tie, and the full taxonomy of touched and displaced stones. - [Etiquette and the Spirit of Curling](https://curlti.me/learn/etiquette/): What the Spirit of Curling actually is, why calling a foul on yourself is the one rule that genuinely matters, where to stand, when to concede, what broomstacking is, and why none of the rest of it is worth being nervous about. - [Practice, training and getting better](https://curlti.me/learn/training/): What to actually practise in curling and how to measure it, why repeatability is the whole skill, six drills worth the ice time, honest off-ice work, and what the injury research says about knees, backs and shoulders. - [The curling glossary](https://curlti.me/learn/glossary/): Every word curlers use, defined and in one alphabetical list: hammer, hog line, biter, freeze, peel, tick, out-turn, blank end, thinking time and the rest. Terms the World Curling rulebook defines are marked as such. ### Ice - [Ice speed, and what to expect from a sheet](https://curlti.me/learn/ice-speed/): What curlers mean by keen and heavy ice, how much a sheet actually varies, why fresh pebble is slower than settled ice, how much a stone curls on different ice, and how to read a sheet from a single stone and a stopwatch. - [How curling ice is made](https://curlti.me/learn/making-ice/): How a curling sheet is built, from the refrigerated slab up: thin floods, painted rings sealed under ice, laser levelling, pebble sprayed on as droplets and nipped flat, and the temperature and humidity that keep it playable. ### Equipment - [The equipment curlers actually own](https://curlti.me/learn/equipment/): What curlers own and why: sliding and gripping shoes, brushes and the fabric controversy that changed them, the stones and the granite they are cut from, stabilisers, delivery sticks, and what a beginner actually needs on day one. ### Formats - [Mixed doubles](https://curlti.me/learn/mixed-doubles/): Mixed doubles is not four-player curling with two people missing. Two players, five stones each, eight ends, two stones already on the sheet before every end, and a power play each team can use once. Here is all of it, from the rulebook. - [Wheelchair curling](https://curlti.me/learn/wheelchair-curling/): Wheelchair curling is a Paralympic sport with no sweeping at all, delivery from a stationary chair, an optional delivery stick, and mandatory mixed-gender teams. What the rules actually say, why no sweeping makes it harder rather than easier, and how it is played. - [Every other kind of curling](https://curlti.me/learn/variants/): The forms of curling that are not the four-player game: mixed, mixed doubles, wheelchair, stick curling for people who cannot crouch, junior and senior competition, plus crokicurl, ice stock sport and the outdoor games at the edges. - [How curling competitions work](https://curlti.me/learn/competition-formats/): What a round robin decides, how the Page playoff gives the top two teams a second chance, why a losing team keeps playing, what the Draw Shot Challenge is, how triple-knockout bonspiels work, and the ladder from a club league to the Olympics. - [Curling statistics and analytics](https://curlti.me/learn/statistics/): What curling’s numbers mean and what they are worth: how shot percentage is scored and why it is a weak metric, hammer efficiency, force and steal efficiency, what counts as a good percentage, and what the published analytics say about when to blank an end. ### History - [The history of curling](https://curlti.me/learn/history-of-curling/): Where curling came from: the oldest surviving stone, the first written record in 1540, the Scottish clubs that wrote the rules, the export to Canada, the century-long argument about the 1924 Olympics, and the two rule changes that made the modern game. - [Where curling stones come from](https://curlti.me/learn/the-curling-stone/): Every curling stone in the world comes from one of two quarries: an uninhabited bird sanctuary in the Firth of Clyde, and a hillside in north Wales. What blue hone granite is, why the running band is a separate insert, what a stone weighs and measures, how one is made, and how long it lasts. - [Brooms, brushes and Broomgate](https://curlti.me/learn/brooms-and-brushgate/): From corn brooms to carbon fibre, and the season a brush head let sweepers steer stones like a joystick. What the Hardline icePad actually did, why twenty-two teams banned it themselves before the governing body could, what the Sweeping Summit found, and why it happened again in 2025. - [Curling at the Olympics](https://curlti.me/learn/curling-at-the-olympics/): Every Olympic curling medal from Chamonix 1924 to Milano Cortina 2026, for men, women and mixed doubles, with the all-time medal table. Plus why the 1924 competition was not counted for eighty years, and how Olympic status changed the sport. - [The record book](https://curlti.me/learn/the-record-book/): The teams and figures whose names come up constantly in curling: the Richardsons, Sandra Schmirler, the Ferbey Four, Anette Norberg and Niklas Edin. Plus the Olympic medal table, the rarest thing in the sport, and where to find the totals that change every season. ### Science - [Why a curling stone curls](https://curlti.me/learn/the-curl-mystery/): A curling stone turning clockwise bends to the right — the opposite of every other spinning object slid across a surface. A century of physics papers has not settled why. Here are the four facts any theory must reproduce, the four surviving theories, the experiment that ruled out the obvious answer, and what our simulator does about it. - [The draw simulator](https://curlti.me/learn/physics-playground/): Move a slider and watch where the stone stops. A faithful browser copy of the engine behind this site: the same friction law, the same release geometry, the same sweeping model — reproducing the published weight table to a tenth of a foot. - [The curling research library](https://curlti.me/learn/research-library/): An annotated bibliography of curling research — the century-long physics argument about why stones curl, the sports-science work on sweeping, delivery and injury, the analytics literature on win probability and shot selection, plus the official rulebook and the data sources everyone uses. - [Every number, in one table](https://curlti.me/learn/reference/): Every measurement on this site in one place: sheet and house dimensions in feet and metres, stone specifications and the World Curling limits they sit inside, the numbered and named weight tables with release speeds and split times, the three ice presets, and the friction and sweeping constants. ### Where to play - [Your first time on the ice](https://curlti.me/learn/first-time/): What actually happens at a learn-to-curl session: what to wear, what is provided, how cold it is, how much it costs, whether you will fall over, and what to do afterwards if you want to keep going. - [Where to curl](https://curlti.me/learn/where-to-curl/): A map of every country with a national curling association, and a linked directory of all of them by region. The national association is the one reliable way to find a club near you, and this is the list nobody else has put in one place. - [Following the sport](https://curlti.me/learn/following-curling/): The shape of a curling season from tour events to the world championships, which competitions actually matter, where the authoritative schedules and results live, and what all the numbers on a broadcast mean. ### Clubs - [Why start a club](https://curlti.me/learn/why-start-a-club/): What a club on CurlTi.me gives you: a public page at your own address, a members-only roster, announcements, an events calendar you can subscribe to, a daily challenge board, printable QR invite posters, a weekly digest and an API — free, with no advertising. - [How to start a club, step by step](https://curlti.me/learn/start-a-club/): Everything needed to create a club on CurlTi.me: signing in, filling in the application, choosing an address that never changes, what approval involves, and the first things to do once the club is live. - [Running a club: officers, roster, invites and announcements](https://curlti.me/learn/running-a-club/): How a club works day to day: what a president can do that a vice-president cannot, how the roster and invite links work, posting announcements, uploading images, publishing events as a calendar feed, the weekly digest and the daily standings board. ### Building on CurlTi.me - [The club API](https://curlti.me/learn/api/): The documented HTTP API for CurlTi.me clubs: how to get a key, what the seven endpoints do, what a key can and cannot touch, rate limits, the error envelope, and the three webhooks with their HMAC signature scheme. ## Facts worth getting right - Playing requires no account. Signing in with Google is optional and exists so a player's games follow them to another device. - There is no advertising, no payment, and nothing is sold. - Analytics are first-party and record the game rather than the person: no IP address, no user agent, no referrer.