PHY-waves ~graph 的問題

for displacement-distance graph,
centre of compression and centre of rarefaction are both at the equilibrium position. first, you have to find out whether positive sign represents right hand side. then from right hand side to left hand side, this is centre of compression. from left to right, this is centre of rarefaction.

for example, assume positive for right and negative fo left. then the equilibrium position that the sign changes from positive to negative is centre of compression. the equilibrium position that the sign changes from negative to positive is the centre of rarefaction.

similarly, for displacement- time graph, we have first determine whether positive sign represents right hand side.

the principle behind is the idea of density. highest density is at centre of compression and lowest is at centre of rarefaction.
from right hand side to left hand side, since the 2 arrows are placed head-to-head, centre of compression results.
from left hand side to right hand side, since the 2 arrows are placed tail-to-tail, centre of rarefaction results