Kerstin sends two crests toward each other on a rope and watches the middle. For a moment, the rope leaps higher than either crest alone.
Two overlaps can look completely different. Some build a bigger displacement, and some nearly flatten the rope. This lesson sorts every overlap into one of those two kinds.
A 3 cm crest meets a 2 cm crest. Both displacements are on the same side, so they add to a larger displacement: 3 + 2 = 5, a 5 cm crest for a moment.
An overlap whose displacements add to a larger displacement is called constructive.
Now the same rope, but the 2 cm crest is replaced by a 2 cm trough. The displacements are on opposite sides, so they cancel toward zero: 3 - 2 = 1, only 1 cm left.
An overlap whose displacements cancel toward zero is called destructive.
Now the 3 cm crest is replaced by a 3 cm trough, so a 3 cm trough meets the 2 cm trough. The side each displacement is on decides the sort, not whether the pulse is a trough.
Both displacements are on the same side, downward. They add to a larger displacement, a 5 cm trough, so this overlap is constructive.
On a pool divider rope, a 4 cm trough meets a 1 cm trough. Is this overlap constructive or destructive?
Both displacements are downward, on the same side.
They add to a larger displacement: 4 + 1 = 5, a 5 cm trough.
Constructive.
A 6 cm crest meets a 2 cm trough on a cord. Is this overlap constructive or destructive?
The displacements are on opposite sides.
They cancel toward zero: 6 - 2 = 4, smaller than the crest alone.
Destructive.
On a rope, a 7 cm trough overlaps a 2 cm trough. Is this overlap constructive or destructive?
A 4 cm crest overlaps a 4 cm trough on a cord. Is this overlap constructive or destructive?
A 5 cm crest overlaps a 3 cm crest on a hose. Is this overlap constructive or destructive?
An 8 cm trough overlaps a 6 cm trough on a long rope. Is this overlap constructive or destructive?
A 9 cm crest overlaps a 1 cm trough on a rope. Is this overlap constructive or destructive?
A 3 cm trough overlaps an 8 cm crest on a clothesline. Is this overlap constructive or destructive?
Which overlap is constructive?
What makes an overlap destructive?
Which overlap is destructive?