Siege! Or, ‘How we learned about pivots and counterweights’.

Our recent trip to Odiham Castle to consider ‘how they kept warm in the olden days’ yielded all sorts of treats, not least an unexpected and deliciously welcome lunch at the real ale pub at the end of the canal tow path.  But leaving our stomachs aside for just one moment, the real highlight was actually right at the end of the walk.

The canal adjacent to our parked cars had a wonderfully rustic looking wooden bridge across it and as luck would have it (since PLL the Younger has been studying castles) the bridge was to all intents and purposes, a drawbridge.  Having answered our key question of the day (answer: not very well, it must have been appallingly freezing most of the time) we had plenty of time to explore how the drawbridge worked.

So, exactly what do I have to do to get this thing moving? Press a few of these buttons maybe?

Sadly, it was key operated (“Urgh! It’s electric” groaned A in disgust, although that didn’t stop him testing out the many buttons on the console and poking the keyhole with a tiny stick ‘key’).  So, we weren’t able to test the mechanism of the bridge itself, but the safety barriers were distinctly manual and the Junior PLLs and their ever willing accomplices A and P set about the task of opening and closing it – several hundred times.  Well, maybe just half a dozen times, but boy, was it fun.


A huge counterweight at one end ensured the barrier didn’t accidentally flop down on an unsuspecting car (or, indeed, child).  The older two quickly established that it would take all four children to collaborate to move it even slightly, so PLL the Dad took this opportunity to share his extensive knowledge of levers, pendulums, pivots and counterweights to explain why it was so impossible to start the barrier moving at one end and yet so light to push back up at the other.  He’s a hoot at parties, honest.

He was also collecting tolls each time we strolled by...

Young P also enjoyed repeatedly guiding the barrier into its aperture – quite a tricky task for a five year old, but one he completed with great care and precision, co-ordinating the relatively small slot, the heavy barrier and avoiding trapping his own hand in there too.

We took some time to examine the gap between the road and the bridge, to establish how often we thought the bridge was opened – verdict: not very often. Junior PLL the Younger and P observed moss and dirt wedged in the gap and surmised that it had been some time since the bridge was last opened.  A recalled that the tunnel we’d seen earlier in the day had collapsed many years ago, and had never been cleared, so there was little point in canal boats heading through the drawbridge anyway.

"Yep. It's going to take more than the weight of a skinny 7 year old to lift this bridge."

Of course, no trip outdoors is complete without children climbing all over something that wasn’t intended for that purpose (how I love affordances!).  The drawbridge cables proved irresistible but at least we were able to explore how heavy the bridge must be by testing the rigidity of the cables.

All in all, a very satisfactory Castles outing – with added forces and dynamics, plenty of collaboration and observation and of course, opportunities to poke things with sticks and climb all over them.  Perfect!


One comment on “Siege! Or, ‘How we learned about pivots and counterweights’.

  1. I remember spending a long weekend at a house beside loch gates on a canal (I think that’s what they’re called) – we spent the whole time moving the water and helping the barges to move through the system. Fab!

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