Making a Newton's Cradle

[Matty F]

I wish to make a large Newton's Cradle. That usually consists of five suspended steel balls. Ideally the balls will be at least 2" in diameter or up to 12" or 24" in diameter. If they were steel they are likely to injure childen. So they can't be steel. Billiard balls bounce well but are still too heavy. Golf balls don't seem to bounce properly so they are no good, and are too small. Soccer balls don't bounce that well either. Polystyrene foam is too flimsy.

Any brilliant ideas? I have an idea which I will experiment with.

[Appelation Controlee]

[Andy Dingley]

good for big steel balls

They must learn

[Gordon Henderson]

Looking for something similar some time back, I found this site:

are expensive though, and steel... [1]

My grandfather made me a newtons cradle many (many!) years ago with large "steelies" like these - he soldered/brazed brass eyelets to the top and I made a cradle out of wood and suspended the balls using heavy nylon fishing line.

I was about 8 or 9 at the time - so for the children aspect - teach them to respect it, or it'll bite!

Gordon

[1] I claim no responsibility for loss of work today from those viewing that site! There's 1 or 2 real gems in it and the chap who runs it is fairly amusing hmmself.

[TMC]

I may be wrong but I thought that the weight of the balls was what makes it work

Surely light weight balls would not have the inertia to work

Tony

[Tim Watts]

Yes - I believe I have the answer...

(You can thank my messy sproglets for leaving crap everywhere!)

are made by "Mega Bloks" (spelling correct). Can't find a source, right now, think we got them at ToysRUs or Argos a few years ago.

They are a giant sized version of "MagNext"

The balls are hollow steel getting on for 3" diameter. Very light, but one thing I noticed was they bounce extremely well on concrete (and thus, probably, on each other - which makes sense - they are exhibiting the restitution of steel without the bulk mass). I think they will work for you.

You may need to go hunting though - can't find them on google shopping. Charity shops would be one place, or ebay. The original pachkaging was a platic tub about 5" deep, 12" tall, 18" wide (all +/- few inches!).

Stop press...

Just found them:

They are called "Magnetix Jr" (or Junior) and there are a few places selling them, eg:

[Cicero]

=====================================================================

Ball float valves (part of - as used in toilet cisterns etc.) - could be filled with water or lead shot. They're cheap and have a built-in thread for suspension. I don't know what effect the water would have - might act as a shock absorber.

Cic.

[Tim Watts]

I did ponder that. Yes, brass float balls might work. Don't think plastic would be any good. Water would probably be the best medium, lead would probably damp it though.

Glass balls would work *really* well, if you could find some that didn't shatter on impact (try dropping a marble onto an anvil).

[Matty F]

That might be OK in the UK but in NZ we have a government department that will prosecute someone making a device that they consider dangerous. The inspectors that I've seen are women.

[Adrian C]

Good grief.

The inspectors that I've seen are women.

Close down all cookware and dressmaking shops :-)

[Matty F]

I think hollow steel balls would work. Brass ones are probably too flimsy. Some kind of hard plastic might do. I'll do some experiments tomorrow.

[dennis]

It will work with anything that is elastic. Heavy steel works well as you can put in lots of energy that is absorbed slowly by the air/sound/non elasticity giving more bounces. Feathers would probably work in a vacuum.

[Cicero]

======================================================================

Replying to both...

I think the brass (or copper) type might work without denting each other if you could fill them completely with water and seal them. Some have a ridge around the 'equator' which might spoil the effect.

Balls for float valves are now mostly plastic so they would be a readily available source for hard plastic balls either empty or water (or possibly lead shot substitute from a fishing shop) filled.

Cic.

[Tim Watts]

So you can't use chain and cannonballs then... :(

[Owain]

Could you inflate spacehoppers with squirty foam?

Owain

[Bruce]

Sounds like a good idea. We are supposed to have something similar in Europe but it apparently relies much too heavily on self-monitoring and -certification.

In what way is that relevant, or noteworthy?

[mark]

I think you would need to get hold of some industrial size ball bearings, 2" plus in diameter. You need weight for inertia and hardness for bounce. Ball bearings wouldn't be drillable so some sort of glue for attaching eyes for suspending them would be the way to go.

mark

[Matty F]

The two I saw had no mechanical sense whatsoever. Situations that have existed for 40 years or more and which have never caused any accidents or problems, they saw as needing urgent attention. e.g. someone climbing a ladder without a safety harness and helmet.

[Huge]

I ground a flat on them and brazed some brass nuts on.

[Jules Richardson]

You just need some big pressure-sensitive switch on the ground, activating some mechanism to stop things dead if the switch is tripped. Unless the little buggers decide to meddle from above, I suppose... :-)

cheers

Jules