(10 marks) Phy. questions about WAVES (6)

You can find the clues in a d-t graph.
The one at the crest or the trough is momentarily at rest.
The one at the middle is either moving upwards or downwards.
If the wave goes to the right,
the particles in the middle is moving downwards.
Otherwise, it is moving upwards.

Using another method in longitudinal wave:
the particle in the middle of the compression is momentarily at rest.
but you cannot determine whether the one in the middle of the rarefraction is moving upward or downward as it is a longitudinal wave.
You can only find out the clues when the longitudinal wave is drawn like a transverse wave.