Posted on 24 March 2011 at 16:14h

I often think how unrealistic a lot of the physics that we teach at this level is. How many times do you come across motion with constant acceleration or a square block sliding down an inclined plane? Well I've seen one now. Due to my interest in rock climbing I know the position of every large boulder within a 10km radius of my house, so when one moves I know about it. Earlier this week the boulder in this photo was at the top of the hill, It had a very interesting overhanging front face. I even went up to try to climb it once but the landing was too bad, in fact there wasn't a landing just a very steep slope.  When a boulder sits on an inclined plane the component of the weight acting down the slope is balanced by the friction acting up the slope. On Monday it rained a lot reducing the friction, the component of the weight was now bigger and the stone started to accelerate down the slope coming to rest on the less steep lower part where the forces were again balanced.

Well it would be nice if simple physics could be used to explain this event but it probably wasn't like that. The stone was actually sitting on a ledge made of loose stones and mud, the rain washed away the ledge allowing the stone to roll down the slope, an altogether more complicated problem. I really wish it had slid because then the interesting overhanging face would have a nice landing.