Spring questions catch out more children than almost anything else in PSLE Science, and usually it is not the physics that does it. It is one word.
A spring has a length before any load is hung on it. Add a load and it gets longer — but the extension is only the amount it stretched BY, measured from where it started. Extension begins at zero. Length never does.
In this clip: the two kinds of spring and which direction each one moves, then the distinction that costs the marks, drawn out to scale — a spring 2 cm long that stretches to 5 cm has an extension of 3 cm, not 5.
A P5 to P6 Science idea that turns up again and again in PSLE Science papers.
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