## Phase Differences in Standing Waves

When a standing wave is formed on a string, points on the wave vibrate up and down. All points on the string between the same two nodes have maximum displacement at the same time, and zero displacement at the same time. They are always moving in the same direction. Points between the same two nodes are 'in phase'.

All points between A and B are in phase with each other.
points between B and C are in phase with each other but out of phase by
$\pi$
with points between A and B.
Points between C and D are in phase with each other but out of phase by
$\pi$
with points between B and C, and out of phase by
$2 \pi$
with points between A and B.
Points between D and E are in phase with each other but out of phase by
$\pi$
with points between C and D, and out of phase by
$2 \pi$
with points between B and C, and out of phase by
$3 \pi$
with points between A and B