Measuring volume by displacement is one of the first practical methods in the syllabus, and it has two traps in it that cost marks.
A stick is lowered into a bottle of water and the level rises. It is tempting to call that rise the volume of the stick – but only part of the stick is under the water. The water can only tell you about the part that is actually in it. The whole object has to be submerged.
The palm fruit shows the second trap. Push it under with a finger and the level rises more – but some of that rise is the finger. You are now measuring your hand as well as the fruit.
The method that works: mark the original height, press the object fully under without adding anything of your own, read the final height, and take the difference.
Filmed at East Coast Park with a cut-down plastic bottle, a piece of driftwood and a palm fruit.
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