Stability

A body tips over when the straight line down from its centre of gravity leaves its base. The centre of gravity of a uniform box is at its middle, so the box tips when the gradient of the board (the cm it rises for every 10 cm across) reaches the width of the box divided by its height. For blocks stacked, or the parts of a flat plate, the centre of gravity is the average of the centres of the parts, each counted by its weight or area; a cut-out counts as negative area. A plank tips about the edge of a table when the turning effects on the two sides are equal. Boxes are drawn to scale where the picture says so.

• 3:00 on the clock, and it only runs while a question is on screen.
• Questions get harder as you answer correctly and easier when you miss. You start at the first level.
• Until your first miss, every right answer jumps a whole band. After it, three right answers in a row jump a band, and a miss drops one.
• A right answer scores the question's points; a wrong one costs half as many. Guessing does not pay.
• Keys 1–4 or A–D pick an option.