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55 projects for age 9 · page 5 of 5

A chemical reaction: an acid (vinegar) and a base (baking soda) make carbon dioxide gas, which is the fizzy foam.

Vinegar (an acid) dissolves the hard shell, leaving the bendy membrane - and the egg swells as water moves in (osmosis).

Red cabbage juice is a natural indicator - it turns pink in acids and blue/green in alkalis.

Cushioning and slowing a fall (forces and impact) to protect a fragile object.

Filtering removes bits from dirty water; layers trap different sizes of dirt (but don't make it safe to drink).

A cushion of escaping air reduces friction, so the disc glides almost freely.

Dissolving, saturation and evaporation - crystals form as water leaves behind the salt or sugar.

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