OT Barton's Pendulum

[ehsjr]

If you've built a Barton's Pendulum, your insight could help.

I'm looking for "how to construct" advice to build a Barton's Pendulum
for teaching the kids. Where I have trouble - and the kids will too -
is tying the strings such that they end up at the exact proper length.
This is not an issue with most of the pendula, but you want the driver
and the target as close to each other in length as possible to get
resonance, or as close to resonance as possible.

I Googled, and there's lots of references to Barton's Pendulum, but I
didn't find anything on construction method. I suppose if I was an
expert on knots I could get the exact length, but I'm not. I have
an as yet untried idea: I could use turnbuckles as the bobs and adjust
the length that way to get it exact. I intend to try that next week
when I can go to the hardware store.

In the meantime, I figured someone here may have done the same thing,
and can offer advice from their experience. Also, is it easier to
get an effective demo out of a larger system? At present, my longest
pendulum is ~9 " and every one I saw on YouTube is a lot larger.

The bigger ones make transportation & setup more difficult - the space
for the demo is somewhat limited. The small one I built works ok
for me, but only ok, not great. But I already know what the thing
demonstrates - the kids don't. For 8 to 11 year olds, you want a
really obvious demo. And you want them to be able to build one for
themselves, with some help.

Thanks,
Ed

 

[ehsjr]

What's the matter with this:
http://sciencedemonstrations.fas.ha...ram_name=indepth.html#a_icb_pagecontent263160

The site does not tell me how to achieve equal lengths when I tie the
string. As I stated: "Where I have trouble - and the kids will too -
is tying the strings such that they end up at the exact proper length.
This is not an issue with most of the pendula, but you want the driver
and the target as close to each other in length as possible to get
resonance, or as close to resonance as possible."

Ed

 

[IanM]

The site does not tell me how to achieve equal lengths when I tie the
string. As I stated: "Where I have trouble - and the kids will too -
is tying the strings such that they end up at the exact proper length.
This is not an issue with most of the pendula, but you want the driver
and the target as close to each other in length as possible to get
resonance, or as close to resonance as possible."

Ed

The driver wants to be fairly massive so it stores plenty of energy. If
you make it out of a stack of fender washers on a fully threaded eye
bolt, between two nuts you can easily adjust the effective length by
moving the whole stack up or down the bolt.

If you want an easy way to make fine adjustments, add an extra nut which
needs to be a fairly well worn nylock (so it can be turned by fingers)
with a gap between it and the washer stack nut, then adjust the nylock
up or down to fine tune the center of mass and thus the length. It can
be above or below the stack.

 

[amdx]

If you've built a Barton's Pendulum, your insight could help.

I'm looking for "how to construct" advice to build a Barton's Pendulum
for teaching the kids. Where I have trouble - and the kids will too -


The bigger ones make transportation & setup more difficult - the space
for the demo is somewhat limited. The small one I built works ok
for me, but only ok, not great. But I already know what the thing
demonstrates - the kids don't. For 8 to 11 year olds, you want a
really obvious demo. And you want them to be able to build one for
themselves, with some help.

Thanks,
Ed

Can 8 to 11 yr olds use super glue, (probably not, they've taken away
their dodge balls)
Anyway, tie the strings to the the string, then thread a string through
a cup, slide the cup to the proper measured position and put a drop of
superglue on the cup/string connection.
Mikek

 

[Martin Brown]

If you've built a Barton's Pendulum, your insight could help.

I'm looking for "how to construct" advice to build a Barton's Pendulum
for teaching the kids. Where I have trouble - and the kids will too -
is tying the strings such that they end up at the exact proper length.
This is not an issue with most of the pendula, but you want the driver
and the target as close to each other in length as possible to get
resonance, or as close to resonance as possible.

Harvards instructions are about as clear as they get.

http://sciencedemonstrations.fas.ha...ram_name=indepth.html#a_icb_pagecontent263160

"Belmont springs" drinking cups are hard to find on this side of the
pond but N identical objects of about the right mass should do. At this
time of year identical Xmas baubles would be a nice touch if this is for
a Christmas popular science lecture for children.

And you can make the length of the driver adjustable with a bit of
cunning. Trapping the thread between a pair of washers on a bolt to
adjust its length for instance.

I Googled, and there's lots of references to Barton's Pendulum, but I
didn't find anything on construction method. I suppose if I was an
expert on knots I could get the exact length, but I'm not. I have
an as yet untried idea: I could use turnbuckles as the bobs and adjust
the length that way to get it exact. I intend to try that next week
when I can go to the hardware store.

In the meantime, I figured someone here may have done the same thing,
and can offer advice from their experience. Also, is it easier to
get an effective demo out of a larger system? At present, my longest
pendulum is ~9 " and every one I saw on YouTube is a lot larger.

The bigger ones make transportation & setup more difficult - the space
for the demo is somewhat limited. The small one I built works ok
for me, but only ok, not great. But I already know what the thing
demonstrates - the kids don't. For 8 to 11 year olds, you want a
really obvious demo. And you want them to be able to build one for
themselves, with some help.

I'd be inclined to carry it a a shoebox full of pendulums and a plank to
hook the thing onto at the venue. Allow plenty of time for untangling
spagetti and running repairs setting up!

Good luck.

 

[ehsjr]

If you've built a Barton's Pendulum, your insight could help.

I'm looking for "how to construct" advice to build a Barton's Pendulum
for teaching the kids. Where I have trouble - and the kids will too -
is tying the strings such that they end up at the exact proper length.
This is not an issue with most of the pendula, but you want the driver
and the target as close to each other in length as possible to get
resonance, or as close to resonance as possible.

I Googled, and there's lots of references to Barton's Pendulum, but I
didn't find anything on construction method. I suppose if I was an
expert on knots I could get the exact length, but I'm not. I have
an as yet untried idea: I could use turnbuckles as the bobs and adjust
the length that way to get it exact. I intend to try that next week
when I can go to the hardware store.

In the meantime, I figured someone here may have done the same thing,
and can offer advice from their experience. Also, is it easier to
get an effective demo out of a larger system? At present, my longest
pendulum is ~9 " and every one I saw on YouTube is a lot larger.

The bigger ones make transportation & setup more difficult - the space
for the demo is somewhat limited. The small one I built works ok
for me, but only ok, not great. But I already know what the thing
demonstrates - the kids don't. For 8 to 11 year olds, you want a
really obvious demo. And you want them to be able to build one for
themselves, with some help.

Thanks,
Ed

Thanks! You all have posted some great ideas.

Ed