What are waves?

3 marks · Normal

In a demonstration, a row of dominoes are stood on end in a line. The first domino is knocked over and the fall continues in a wave down the line. A student says this is just like a water wave. Discuss whether this is a correct analogy for how waves transfer energy.

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The analogy is not fully correct. In a dominoes line, each domino physically moves from its place and the effect is transferred by the matter moving. In a water wave, the water stays in the same place and only the energy travels. So, a dominoes wave moves matter, unlike real waves.

Also accept: Domino analogy involves movement of matter; waves transfer energy only

Common mistakes: Saying dominoes are exactly like waves

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Marking points

M1 · 1 mark · Identifies each domino moves from its place/position.

M2 · 1 mark · States that in real waves, matter does NOT move with the wave; only the energy travels.

M3 · 1 mark · Explains why the analogy is not fully correct (i.e., dominoes involve matter transfer, waves do not).

Worked solution

The domino effect is not a perfect analogy. The fall of each domino causes the next to fall, but the dominoes themselves move from their original position; matter is transferred. In real waves, the water or medium vibrates in place and only energy (not matter) is transferred. Therefore, while both show a transfer of an effect, only real waves transfer energy without matter transfer.