# 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. ## 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 and equipment. - [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. - [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. - [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. ### 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. ### 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.