### Technical and geeky stuff about how it all works…

The patterns of the pendulum wave machine were first seen in 1867 by the Austrian physicist and philosopher Ernst Mach, who built the very first wave machine whilst working at Prague university. Mach built his machine with mathematics and physics, and created something magical, almost metaphysical! If you want to know more about the science-y bits, read on.

#### The basics

For any pendulum, the longer the string, the longer it takes that pendulum to complete a full ‘tick’ and ‘tock’. The amount of time that any pendulum takes to do this, is known as the *period*.

On our wave machine, we have 20 different lengths of pendulum; the longest one takes the longest time to swing to and fro – it has the longest period and appears to be the slowest. The shortest string has the ‘fastest’ pendulum, with the shortest period.

We’re often asked if the weights in our pendulum’s balls are the same. They are, although they don’t need to be, as the weight – or more correctly *mass* – of a pendulum – has no effect on the length of the period. (to understand the difference between *mass* and *weight*, click here.)

So if we want to control the length of time that each pendulum takes to tick-tock, all we need to do is to control the length of the string.

#### The patterns

When we built our wave machine, we chose 20 lengths of string, to make the 20 pendulums ‘beat’ to certain frequencies. When you watch the patterns of the machine, you will see that they return to the starting point, after about a minute – it’s actually 70 seconds after the start when all the balls line up again, in a single row.

In those 70 seconds, the longest pendulum will make 20 ticks and 20 tocks, the next one up, moving slightly quicker, will complete 21, the next 22 and so on, all the way up to the shortest that completes 39 cycles in the 70 seconds.

The patterns that emerge, are a result of the changing relationships between the different frequencies. After 35 seconds, for example, there are ten balls that have completed a full cycle, and are at their starting position, whereas the other ten are exactly half way through a cycle and are at the furthest point in their swing away from the start.

#### The really advanced stuff

If you want to understand some more about what’s going on behind the magic, follow these links for more in-depth information:

http://www.arborsci.com/cool/pendulum-wave-seems-like-magic-but-its-physics

http://io9.com/5825639/a-simple-physics-demonstration-that-shows-why-science-still-sometimes-seems-like-magic

http://sciencedemonstrations.fas.harvard.edu/icb/icb.do?keyword=k16940&pageid=icb.page80863&pageContentId=icb.pagecontent341734&state=maximize&view=view.do&viewParam_name=indepth.html#a_icb_pagecontent341734

http://scitation.aip.org/content/aapt/journal/ajp/69/7/10.1119/1.1349543?ver=pdfcov