Drag the brick stacks onto the plank. The columns hold it level while you set up — predict which way it will tip, then press Remove supports to test. It balances when the anticlockwise and clockwise moments are equal. Grey boxes A and B are unknown masses — tick Show moments · reveal ? to weigh them. A weight on the pivot has zero moment — try it, the beam won’t budge. g = 10 N/kg.

Drag weights from the shelf onto the spring’s hanger. It stretches by e = F ÷ k, so each equal weight adds an equal stretch — until the elastic limit, where the line bends. The grey ? weights are unknown: hang one and the calibrated spring weighs it (W = k × e). g = 10 N/kg.

Turn the tap on to fill the tank, then click the dashed right wall to drill a hole anywhere. Each jet leaves at v = √(2gh) and falls in a parabola — the deeper the hole, the faster it shoots and the further it lands. Click a hole again to plug it.