Thursday, May 15, 2014

Physics - a truck, a lawn mower and a geyser

This is by Doug.  Deanne's guest blogger.....

My dad graduated from the University of California - Berkeley as a Civil Engineer.  In one of his classes, he was the only student to come up with the formula that solved a problem a professor gave the entire class at the beginning of the semester. Needless to say, he was smarter than the average bear.  (No pun intended for those of you who know what the mascot is for Berkeley.) All this was to give you the background as to why my father loved explaining the concepts of physics to me and my other siblings (and whoever else would listen) throughout my life. 

One of the most memorable of these instructional sessions was when I backed his pickup truck into a cement post.  That was back in the late 70's when they built real bumpers with 1/4" steel that easily went through the grill of any car failing to stop at the appropriate distance at stop lights.  After I hit the pole, though it gave me a pretty good jolt, I drove away without looking at the possible damage since I knew how strong the bumper was and it probably wasn't much.  And I wanted to get out of there quickly so I didn't tip off the friends I had just left at the fast food restaurant that I just hit a stationary object. 

On the way home, a police car drove up beside me from behind and as I noticed the officer slowing and staring at the rear of the truck, I had a feeling something was not right back there.  He didn't pull me over so I figured it couldn't be that bad.  After pulling in our driveway, I walked back to take a look, and there was the bumper completely in tact.  It was just hanging down a few inches from the ground.

My dad was surprisingly patient with the whole thing, but here is where a physics lesson had to be taught - when two objects collide, energy is transferred and something has to be displaced if there is enough force.  In this case, it wasn't the bumper, but it was the bolts holding the bumper to the frame that had to give way to the energy caused by a 2 ton truck hitting a 6" steel and cement post. The next day, we headed off to the hardware store and replaced the sheared bolts.  The bumper was as good as new and I was wiser for the experience.

Olivia gained wisdom today in much the same manner.  As you can see by the photos below, something gave way this evening.  In this case, Olivia found out that a self propelled mower can deliver more force than a PVC pipe can resist. The other physics lesson is that a gravity fed secondary water line can build up sufficient pressure to create a 30 foot geyser when that energy is released.
We had the best water feature in the neighborhood tonight!

The kids just went about their business.

Turns out, the city has a policy that they call the fire department for emergencies involving floods.  We had a friendly visit with 3 firefighters that probably were glad to have something to do that did not involve life and death circumstances.  I told the dispatch at the city that is was just flooding the neighbor's horse pasture and they probably appreciated it, but she was determined to get these guys out here.  I think she knew how bored they normally are and that they would like the diversion.

One of them had a daughter in the fourth grade at Clayson's school and he happens to be doing a career day next Friday for all the fourth graders.  He wanted to get this picture of Clayson by the geyser so he could use it in his presentation next week.  Clayson was a bit embarrassed.



  1. Haha, how many geysers have we had total? I feel like we have one every two or three years.

  2. Some of the higher HP model lawn tractors can also be used for occasional snow plowing and other heavier tasks but they are best suited for mowing with or without a grass catcher and pulling a cart.