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## Snow Globe Dynamics

This weekend my daughter received this:

It was a present from her grandma who had just come home from a holiday.

For those who haven’t seen one, it’s what is commonly known as a “Snow Globe”. There us a glass (possibly plastic) sphere set on a base which has a scene. In this case it’s a lighthouse. The sphere is filled with water (a clear liquid at least) and there are little specs of stuff in the water. Often these are white (hence the name “Snow Globe”) but these ones are strange and mesmerising, flickering with colours. Sort of semi transparent but change colour in the light.

I hadn’t seen one for years, and I started spinning it and watching the glitter spin round. I guess I must have had the recent M3 exams on my mind because as I was watching them spin I started wondering what the centripetal acceleration was. As I was thinking about this it occurred to me that this system I was holding wouldn’t obey classical, Newtonian, laws, but would be governed by the laws of fluid mechanics.

I did study fluid dynamics at university, I recall the navier-stokes equations. I recall looking at currents and river flow. I don’t, however, recall discovering how fluids would act when they were in a closed spherical system.

Watching the Snow Globe spin is fascinating. As you spun it, some glitter collects at the bottom, if you alter the direction of spin the rise up into the middle. If you stop spinning it, the contents carries on spinning, if you reverse the spin it still carries on, and you can see the outside slow and change direction first. Due to the friction with the sphere. This then moves the rest of the liquid, but you can get an amazing sight of the outside liquid going one way, but the inside going the other.

When you spin it, or shake it, then leave it to rest the glitter jumps and jives in a brilliant way. It seems like it is a sort if “Brownian Motion“, but I would need to investigate it further.

All in all, I’m fascinated by this Snow Globe, and I am going to read up on fluid dynamics, their effects in a closed spherical system and brownian motion as soon as I get chance.

If you have any suggestions of books, papers, articles, blogs etc on the subject, I’d love to hear them!

Categories: Commentary, Maths
1. June 10, 2014 at 10:24 pm

As a snow globe artist and maker, I have to agree that the objects can be mesmerizing. Although we’ve been making them for years, there is still more to learn. Different glitters and shapes have different effects; changing the liquid even slightly can be wonderful (or cause problems.)
So glad you enjoyed your daughter’s gift. I am endlessly amused by my own snow globes (or water globes … as you say, they don’t always have snow.)

• June 10, 2014 at 10:36 pm

They are pretty amazing. As someone who makes them, do you make different shapes ever? Are any shapes as good (or better) than the standard sphere?

• June 10, 2014 at 10:47 pm

My partner and I tend to make snow globes with round glass globes – although we do work in several sizes of glass. I have not experimented much with domes or other shapes of glass.
The changes we make are to the tiny sculptures inside, to the thickness (viscosity) of the liquid, and to the weight and shape of whatever is floating.
I did create some enchanting “timeless” designs once using tiny watch gears as “confetti” or snow, but sadly, physics does not give any breaks to art and they rusted into orange dust over time. That was enchanting in its own way, watching art slowly rust into nearly nothing …
I’ve also tried to cut unique floating shapes out of thin acetate, vinyl, laminated paper, and so on. The weight and material dictate how quickly they sink — unless they permanently float to the top, they always sink eventually. The outline shapes can help them swirl and float, or a very flat design can create “surface tension” so that the shape sticks unforgiving and immoveable to the side of the glass globe. You can see some of our recent work on our wordpress site.

• June 10, 2014 at 10:53 pm

I will have a thorough look tomorrow. Sounds great!

• June 11, 2014 at 10:46 am

I’ve had a look on your site. Some amazing pieces of art! Incredible.

• June 11, 2014 at 3:49 pm

Thanks. It’s definitely a learning experience.

1. August 15, 2014 at 8:29 pm