Help your child distinguish a boat sinking under weight from tipping because of cargo placement.
Drag the cargo box, or use the sliders.
Water pushes the boat upward. When the boat leans, the underwater shape changes. That push can help the boat stand straight again. Cargo high up or far to one side can make it lean farther.
Stay with your child throughout the experiment. Read the task together, compare your predictions and start the test. Operate the controls, then discuss what changed.
Ask “Where is the boat pushing water aside?” Help children distinguish too much total weight from cargo placed in a spot that makes the boat tip.
Ask: “What did you change? What did you notice? What will you try next?” A different result is a clue, not a bad score.
This is a box-shaped boat in still water. Real waves, loose cargo and leaky seams can change the result.
Use the simulation to discuss patterns. You remain responsible for choosing and supervising any physical activity; real results can differ.
Does lowering the same cargo change its weight or its tendency to tip the boat?
A low cargo position can improve stability but cannot make an overloaded boat carry unlimited weight. This model uses a box-shaped hull in still water.
Open rectangular hull: length 30 cm, side height 8 cm, shell mass 120 g. Fresh water density = 1000 kg/m³. Submerged polygon area × length gives displaced volume; buoyancy = ρgV. At every angle, vertical position is solved so buoyancy balances weight. The horizontal separation of buoyancy and mass centre gives the roll torque. Roll uses a damped rigid-body equation with assumed added inertia 0.2Mb² and damping ratio 0.4 referenced to a 4 cm restoring lever. No waves, pitch, sloshing or structural bending. The calculation stops when a rim reaches the water. Sinking after that event is an illustration; flooding flow is not simulated.
US Naval Academy · Buoyancy and stability
Sources explain the physical relationships. The chosen model parameters and simplifications are listed above.
Quick guide: s = seconds · m = metres · cm = centimetres · g = grams · kg = kilograms.
Water pushes up on the part of the hull below the surface. A tilted boat can push water aside unevenly: that can help it straighten up. High cargo or cargo near the edge can make it tip farther instead.
Fold a small open boat from aluminium foil and float it in a shallow tray. Add identical coins one at a time, first in the centre and then to one side. Record the number it carries before water comes over the edge. Dry the floor after testing.