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.

Standing waves

# Standing waves on strings

A standing wave occurs when two waves of the same frequency and amplitude are moving in opposite directions and interfere with each other. It has certain points (called nodes) where the amplitude is always zero, and other points (called antinodes) where the amplitude fluctuates with maximum intensity. Use the distance between two consecutive nodes or two consecutive antinodes to calculate the length of a standing wave. Created by David SantoPietro.

## Want to join the conversation?

• At , he says the two waves are lining up constructively. But if one is above and one is below the equilibrium point, wouldn't they cancel out?

I'm confused too as to whether we are actually talking about two waves overlapping, or one wave that has gone to the right and then to the left. He said the latter but then why are we talking about interference if it's just one wave? • think about it, he said (more or less) that we're continuously forming disturbances(after talking about pulses),
so, after the first reflection, don't you think at a given instance of time at any point there will be (at least) two simultaneous waves == interference?
As we've defined standing waves to not move right or left (along axis/eq. line), don't you think these points must coincide exactly as they had before to form that exact possible wavelength?
So after the first reflection, the no. of reflections really doesn't matter as they're coinciding at the exact place, further, the ind. waves are moving, so their regions of 'activity'/'disturbances' (except nodes....imagine!it's fun ;}) are changing, so their shifting vertically (here) down and then back up...you know...oscillate! They oscillate up and down! (maybe the flat-line is when they have a complete pi shift overlap= total destructive interference)
[and besides, do we assume the wave to be finite(that is not directly from its source?---> an actual question, not a rhetorical device;)]

at least this is how I've imagined (notice the bold font) it and I'm no professional, if wrong do correct me,
Hope this helps!
Onward!
(1 vote)
• at why does the pulse turns upside down after reflection? • What's the difference between a crest and an antinode? • A crest is a point where height of the wave is equivalent to its amplitude (the highest points on the wave). An antinode is the area that moves the most in a standing wave. Note that all waves have a crest, but not all waves have antinodes.
• At , isn't the wavelength of the third harmonic suppose to be 3/2 not 2/3? there's 1 wavelength + 1/2 wavelength • From what I know, waves are the transfer of energy in the form of a disturbance ( vibration in particles of a medium). If nodes are places where the "string" or any medium does not oscillate does that mean that energy is not transferred at those points of destructive interference? • Actually what does harmonics mean? • The "harmonics" are exactly the "standing waves" that this video is about. The "first harmonic" is the same as the "fundamental" wave that he discusses in the first part of the video. Its wavelength is twice the length of the string.

At in the video, he introduces the "second harmonic", which has a node in the center, and its wavelength is equal to the length of the string. The frequencies of the higher harmonics get higher and higher as the wavelengths get shorter and shorter.
• Can you create travelling waves in a medium that has boundaries? • when we say n is the number of harmonics, what do we mean by a harmonic?   