Problem
A water wave crosses a pond and a leaf floats in the middle. Does the leaf move from one bank to the other together with the wave? Explain.
Solution
No. The leaf does not travel with the wave: it oscillates up and down (and slightly back and forth) around its equilibrium point, returning practically to where it was after each crest passes.
Why. A mechanical wave is a disturbance that propagates through the medium, but the medium itself is not transferred. The water particles (and with them the leaf) undergo small local oscillations; what advances is the shape of the disturbance.
What is carried. The wave carries energy and momentum, not matter. It is the energy that travels from one bank to the other: the leaf receives and gives up energy as it oscillates, but stays in place.
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Topics: Onde Concepts: Onda armonica Skills: Analisi di casi limite e fantafisica