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Question Standing wave

4 months 1 week ago #41384 by Kasey
I set up the standing wave using a vibration generator and a long piece of string.
Main problem is that it moves even though its clamped.
When the students hold the string we get an amazing standing wave.
Is there any way to set it up without using students?
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4 months 1 week ago #41385 by Cathalg
We Clamp the vibration generator directly and omit the retort you have on the left side of your set up.
The other end we use a bench pulley with some masses hanging from a loop in the end of the string. 200g ish. teachers often vary it.
This gives us pretty good standing waves.
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4 months 1 week ago #41386 by dbuchanan
Looks pretty much a standard setup to me. Comparing with how I usual set up, you could try the following...
- Tie the string to the clampstand post, and sit the vibration generator on the clamp stand base?
- Keep the mass hanging down from the pulley at about 100g (couldn't see from picture)
- Shorten the distance of vibration generator to pulley to 1m instead of 2, or put in a bridge (I tend to mis-use a perspex prism) in front of the pulley.

A wild guess might be that the string is stretching over the longer distance, or the signal generator is still warming up, causing frequency to vary?
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4 months 1 week ago #41389 by D.B.Ferguson
Only thing to add is: I would try to have the vib. gen. make contact with the string when it is horizontal (lower the clamp). This means that the oscillation has a rest position in the least stressed position.

Technicians: providing solutions and more.

David Ferguson B.Sc.
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4 months 1 week ago #41391 by bsimmo
That's very similar to my setup, just we don't often clamp the sig gen any more.

Foa slightly better setup, if wanted than a prism on a wooden block can be used just before the pully, but these do haev a tendency to move unless held in place somehow.

You should also be using a square wave... but that never works as well as the sine wave.
Keep the amplitude low as you'll be clipping the wave at the top and bottom and it also helps stop it moving around.

Use Pink/Purple or Blue 'strings' from Aldi/Lidl these can be seen easier, they also have different masses for a-level experiments.
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4 months 1 week ago #41392 by Kasey
"Use Pink/Purple or Blue 'strings' from Aldi/Lidl"

Do you buy these?

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4 months 1 week ago #41393 by bsimmo
Yes, no technical use of colouring and mess here ;-)

Quick look and currently we have
WorkZone "1.7mm polypropylene Twine" (it's great stuff, good for pulleys, trollies etc. That's just white at the moment.
www.aldi.co.uk/twine-for-floor-tilers/p/093352043122005

and

Blue Braided Twine (PolyPropylene also), I think i have it in another colour and we also have some bright pink stuff that's very similar.
It's thicker but works well.
www.aldi.co.uk/braided-twine/p/093352043121804

It's aldi of course, so comes and goes. Lidl will do similar. B&Q, screwfix, toolstation, Asdw may well do their own.

It really depends what you are trying to show.


I believe you can get fluorescent/glow in the dark cord.
or EL Wire ?

If you really wanted to stretch idea, get some of the tiny led cords and vibrate that and then send time pulses down the leds to give some effects. Perhaps something for a student activity over a long time that doesn't mind a bit of microelectronics.

Sorry, may have wandered off into the wishful thinking realm

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4 months 1 week ago #41394 by AndyG
For my penny-worth ... simplify what you already have.
Loop the string directly over the retort rod, rotate the retort base in line with the string and stick the (magnetic!) base of the vib. gen. to it. Clamp the retort to the bench. Tension the string with either another clamped retort or a pulley & weight. If you need the movable pivot, keep it in place on the bench with a little spot of blu tak and if the pivot isn't high enough just stick it onto a wooden block with a blob of blu tack.
A simple, two-retort variant with 'normal' string should give 19 nodes with very little effort ...
Challenge set ... :-)

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