ScienceGrade 2ages 7–8
🪙 Sink and float
A child who has learned "heavy things sink" is stumped when the exact same piece of foil sinks as a tight ball but floats as a boat shape — because weight alone isn't the rule; how the weight is spread out (its shape) matters just as much.
Try this lesson freeNo card needed. The first lesson is free.
Download on the App StoreWhat your child learns
- Something heavy for its size tends to sink.
- Wood often floats — it is light for its size in water.
- The same foil: a tight ball may sink.
- A boat of that foil floats — the shape holds air and pushes water.
The mistake most kids make here
Everything heavy sinks, and all foil always sinks.
Try one question
A tight foil ball can sink and a foil boat float because…
Why different
- the foil turned into gold
- the shape changed
- the water got angry
Answer
the shape changed — Yes. A wide shape pushes more water aside.
How Maya teaches it
Your child tells Maya what they did in class. She teaches this topic at her desk, asks questions with tappable answers, and when the answer is wrong she explains why that answer was tempting instead of saying “try again”. She remembers what did not land and comes back to it.
Your child has it when they can: Say why a foil ball can sink and a boat of the same foil can float.
How to help at home
"Heavy sinks, light floats" is a rule that works often enough in daily life — a stone sinks, a feather floats — that a child reasonably extends it everywhere. The piece missing from that rule is that shape changes how water pushes back, regardless of the material's weight.
Tonight, take a small piece of aluminum foil, roll one piece into a tight, dense ball, and shape another same-sized piece into a little open boat. Drop both in a sink or basin of water. The ball sinks; the boat floats. Same material, same weight — different result.
When your child says "but foil is heavy, it should sink," ask: "did the amount of foil change, or just its shape?" Let her notice that only the shape changed, which means shape — how spread out the material is — is doing the work here, not weight alone.
A good sign she has it: she can predict, before testing, that a flattened, wide piece of clay will float better than the same clay rolled into a tight ball, because she's reasoning about shape and not just "is it heavy."
Questions parents ask
- Why does my child think everything heavy sinks?
- It's a fair generalization from common examples like stones versus feathers, where weight really does predict the outcome. It breaks down with materials like foil or clay, where the same weight can sink or float depending on shape.
- Why does a foil boat float but a ball of the same foil sink?
- A wide, hollow shape pushes aside (displaces) more water than a tight, dense shape of the same weight. Displacing enough water creates enough upward push (buoyancy) to support the object — which the tight ball's small shape doesn't manage.
- Do real boats work the same way?
- Yes — a steel ship is much heavier than water, but its hollow, spread-out shape displaces a huge amount of water, generating enough buoyant force to keep it afloat, the same principle as the foil boat.
- How does Maya teach this differently from just saying 'shape matters'?
- Maya asks the child to compare the same material in two different shapes and describe what changed, so she discovers that shape — not just weight — affects floating, rather than being told the rule directly.
No card needed. The first lesson is free.
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Sources: Next Generation Science Standards