9.8 metres per second per second

Climbers on Arboneum (5), Oeschinensee, Kandersteg, Switzerland.
Photo Rachel Berkowitz, Jan 2011

Gravity.  It works every time.

In day-to-day life, people don't really think about it all that much.  I doubt that many people have much concept of how fast 32 feet per second per second is.  But last week, I got a very good visualisation as a 3m x 2m x 5m-long icicle broke off from an overhanging rock several hundred metres up the side of a mountain and came tumbling down just the other side of the rock from the two climbers pictured in this photo.

The icicle shattered into watermelon-sized shards as it boomed its way down the chute.  Accelerating at 9.8 ms^-2, one of these blocks would be plenty to kill a person.  Fortunately the two gentlemen climbing that particular icefall at the time were well sheltered at a bolted belay stance around the corner of a rocky ledge.  The part of the icicle still attached to the cliff far above now exposed a gaping hole in its centre.

That day was warmer than it had been for awhile, so the booming of ice pillars as they tumbled off their perches was audible throughout the valley (and did not increase my confidence in ice climbing).  But the air temperature was increasing; a temperature inversion meant it was warmer higher up the valley walls where the hanging icicles were; the ice began to melt and solid slowly turned to liquid; the ice core was no longer solid and the structure of the icicle was compromised; then the perfect combination of thermal and fluid dynamic conditions were tugged on by gravity and the whole thing collapsed.

It makes me appreciate physics more.