Mirrorturn rules and controls
Mirrorturn is a spatial puzzle: two models made of balls and sticks stand side by side, both built from the same balls. You turn them and decide whether it is the same model, just turned differently, or its mirror image. Free in the browser, no account.
There is a clock only in the Expert profile, and no leaderboard at all. The points count only for you, and a new run only begins when you start it.
How it works
- Three profiles: Beginner with twelve rounds on three levels, Standard with fifteen rounds on five levels, Expert with nine rounds on the three top levels and a clock of 20 seconds per round. Whether a pair is the same or mirrored is drawn afresh every round - never more than three equal answers in a row.
- Five levels: Easy, Medium, Hard, Very hard, Master. From the Hard level on the letters on the balls are gone, on the Master level the colours too, and there only model A can be turned - model B stands still. After the answer everything is visible again.
- Turn: drag a model with the mouse or your finger; the mouse wheel zooms. With the keyboard: Tab picks a model, the arrow keys turn it, Q and E roll it, plus and minus zoom.
- Decide: “Same” if a rotation is enough, “Mirror image” if no rotation puts B exactly onto A. On the keyboard these are the keys 1 and 2.
- Answer: after every answer a sentence explains what you saw. “Compare orientation” turns B exactly like A - then you can see for yourself whether the balls lie on top of each other.
- Points: a correct answer is worth 100 points, 60 with a nudge; there is none on the top two levels. Wrong answers cost nothing. If the clock runs out in the Expert profile, the round doesn't count - you still see the answer, and the next round waits for you.
The letters on the balls tell you which ball is which - C, H, F, Cl, Br and O. “Show letters” switches them off; then you practise recognising the balls by size and colour. On the high levels the game takes letters and colours away, and after the answer they come back.
One pair, step by step
The model below is the one from the Easy level: a middle ball with four different balls attached. The rotations are calculated, not drawn; what is written under each picture comes from where the balls actually are. “At the front” means: on your side.
Step 1One ball as an anchor - The H ball appears only once in this model. Turn both models until it sits at the top. After that only one movement is left: turning around that ball. The H ball is now at the top in both models.
Step 2Fix a second ball - Now turn around the H ball until the F ball is on the same side in both models, here on the left. Nothing more can be lined up without moving the first ball again. H at the top and F on the left, in both models.
Step 3Compare the last two - Now everything comes down to Cl and Br. If they sit the same way in both models, it is the same model. If they are swapped, B is the mirror image - and then no rotation helps any more, because every further turn would move H or F out of place. Model A: Cl at the front, Br at the back · Model B: Cl at the back, Br at the front. Cl and Br are swapped - B is the mirror image of A.
Step 4The cross-check - The same with a different pair: here B is only turned differently. After the same two steps Cl and Br match as well, and in the game “Same” would be the right answer. Model A: Cl at the front, Br at the back · Model B: Cl at the front, Br at the back. Cl and Br match - B is the same model as A.
Why a mirror image never fits exactly
When four different things hang on one ball, the model comes in two versions that are mirror images of each other - like your left and right hand. However you turn them, they never line up exactly. In chemistry such molecules are called chiral, from the Greek word for hand, and the two mirror-image versions are called enantiomers.
The models in the game are real small molecules, shown in simplified form: the balls are atoms, the sticks are the links between them. You still don't need to know any chemistry - it is all about turning and comparing.
Play it yourself
Mirrorturn runs in the browser, with your finger on a phone and with the mouse or keyboard on a computer. You only need a connection, because every answer is checked on the server.