If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Precalculus (Eureka Math/EngageNY)>Unit 4

Lesson 3: Topic A: Lessons 5-6: Tangent lines and wave functions

# Wave interference

Let's explore wave interference and solve a few examples to find the value of the total wave when two wave pulses overlap. Created by David SantoPietro.

## Want to join the conversation?

• What is the reason behind superposition? Why waves behave this way?
• Think about this way: Waves are disturbances right? So if you consider an example of force: say you're pulling a rope in x direction and your friend is pulling it in -x direction, with equal forces. It doesn't move as the forces cancel out. Same is with a wave.
1 wave disturbance is moving the rope up the other is moving it down so if they're equal they cancel each other out. If not then you use the same principle.
In case of EM waves, I think it's the electromagnetic force that causes it.
• what happens if two waves overlapped and they were moving in the same direction
• its an interesting thought...

can you think of an example of that happening?

I think that they would interfere in just the same way as any other waves. You would see a 'wave' which is a combination of thm both...
• But how do individual pieces of the string know? They only know that adjacent pieces of the string pull them up or down, why would two opposite waves pass through each other when they would make the string straight at some point(since they're opposites of each other).
• They don't KNOW it. You see if something is being pushed up and you push it up more it gets pushed higher (or you might pull it). Same is with the waves, one wave pushes it up and the other wave also pushes it up so it adds up.
• Is the energy in a wave conservative ? if so why the waves will get reflected when they hit a wall or an open end ?
(1 vote)
• I think the waves get reflected when they hit a fixed point because of newtons third law, so the pulse tries to move the wall up like it did to the string but since wall is denser than the string it hits the string back with a pulse in the opposite direction with equal magnitude which is why you get a inverted pulse. I hope that's what you were asking.
• Does this work with both transverse and longitudinal waves? I can see how the transverse behave this way, but the longitudinal? In displacement displacement graph, will there be anything to overlap?
• What is the reason behind superposition? Why waves behave this way?
(1 vote)
• You'd have to think of a wave as a set of disturbances, rather than a cohesive structure. If two waves crash head-on, the disturbance at one point is the sum of the disturbances that the waves would have caused individually. Waves don't really interact with other waves, and all we can see is their combined selves, even though all it is is the sum of the disturbances.
• How can he add those two waves and the third wave will be three units high? They are both in the opposite directions. Why wouldn't the waves cancel each other @
(1 vote)
• The direction the waves travel doesn't matter, unless one is moving underneath the other wave, if that makes sense. The waves' amplitudes are both positive, so they add together. If the waves' amplitudes were negative, you would add the negative values(-2+-1=-3). But for this scenario you would still add 2+1=3. Hopefully this helps!
• As many others here are asking, why don't they just cancel? I'm imagining two ocean waves coming at each other in opposite directions and I imagine them cancelling.
(1 vote)
• If the waves are perfectly aligned and of the same frequency, and equal but opposite amplitude then they will cancel out. If they are not perfectly aligned, same frequency and equal but opposite amplitude they will not cancel out perfectly.

If the wave are traveling opposite directions they waves will not be perfectly aligned they will at one time have their peeks in sync and others a peek will coincide with a trough so there will not be a cancelation.