Q.Distinguish between a progressive (travelling) wave and a stationary (standing) wave, with reference to how each transports energy through the medium.

In a progressive (travelling) wave, the disturbance -- and the energy it carries -- steadily advances through the medium in a fixed direction; every particle of the medium eventually receives, and later passes on, the same disturbance (with a growing phase lag), so a progressive wave is the mechanism by which a source transmits energy to a distant point.

A stationary (standing) wave, formed by the superposition of a wave and its own reflection, has a very different character: its amplitude pattern -- alternating nodes (zero displacement always) and antinodes (maximum displacement) -- is fixed in space and does not travel at all, even though each particle between two nodes still oscillates in time. Because the pattern itself never moves, no wave is actually advancing past any point in a net sense (the incident and reflected components are travelling in exactly opposite directions with equal amplitude, so their energy flows exactly cancel on average); energy merely oscillates back and forth locally within each node-antinode segment, never being transported from one end of the stationary-wave region to the other.

Contrast whether the wave's overall pattern advances through space (progressive: yes, and energy travels with it) or stays fixed (stationary: no net energy transport).

• Thinking a stationary wave carries no energy at all (it does -- energy is present and continuously exchanged locally -- just not transported net along the medium).
• Confusing 'stationary' (the pattern doesn't move) with 'the particles don't move' (particles between nodes still oscillate; only the nodes themselves are permanently at rest).