How about a very old poem to get it in perspective?
Little birdie in the sky dropped some whitewash in my eye.
I’m not mad, I won’t cry. I’m just glad that cows don’t fly.
Sue CQ
SueCQ
How about a very old poem to get it in perspective?
Little birdie in the sky dropped some whitewash in my eye.
I’m not mad, I won’t cry. I’m just glad that cows don’t fly.
VERY FUNNY
Crows and seagulls often will pick up objects like small clams and nuts and then drop them on to pavement to crack open the shell. Perhaps the splatter was the a smashed clam or some such object and not bird poop.
Bird poop may have some sort of acid in it. Birds are diverse eaters, you know. It can get into the microscopic cracks, and weaken the windshield, which will then explode. Or it simply can be the moisture that freezes at night and expands those cracks. The layer of poop on top may keep it from drying as it may have some undigested fat in it. So the process will repeat itself every night for a few nights.
Or it may be simply vandalism – someone hitting the windshield with a hammer right where bird poop is, hoping to cover his tracks this way.
I heard the car talk story about the FAA having a machine to test bird strikes, and lending it to the Brits.
More than 10 years ago I worked with a guy who had worked at a UK manufacturer of jet engines (lets call them PE), in the engine testing facility, maybe 5+ years earlier. His job was to machine fan blades to insert tiny explosive charges, to help understand what happens when one breaks. He said that is more predictable and reproducible than firing a chicken, but hey you Americans do love your guns:-)
He had two stories. The first one was about a young apprentice who had joined PE straight from school, and he was given the job of going out to buy some chickens, and loading the compressed air ‘cannon’. He destroyed some very expensive prototype. The punchline was the same, defrost the chickens.
The other was exactly the reverse of the car talk story, which was an “American organisation” approached PE (and presumably others) for discussions about standardising tests for bird strikes, and plans for the ‘cannon’ were sent. Some time later, PE was contacted again. The tests completely destroyed windscreens and jet engines, and things looked very bad. Punchline, yes, defrost the bird before firing, but use chickens not turkeys.
This is in reference to the show about the bird poop and the cracked windshield. My husband is a saltwater fisheries biologist. He said that he has found many otoliths or fish ear bones which can be the size of small stones in the poop of terns. If a seabird or other large fish-eating bird swallowed a large enough fish it could excrete one of these otoliths in its poop when flying because they are not digested.
Some significant physics is missing in Wolfgang’s description.
In addition to the factors mentioned by Wolfgang there are two other important stone vs poop comparisons that must be considered to determine the force on the windshield:
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Using terminal velocity, density, etc, he compared the impulse of poop with the impulse of a stone. The length of time it took the poop to complete its impulse must be compared to the length of time it took the stone to complete its impulse
Why? Because force = (impulse) / (time of impulse) , or, as Newton wrote,
F = (change in momentum) / (change in time) (he did not say F = ma)
As Wolfgang said, change in momentum is impulse, however, since the stone bounced off the windshield it was in contact with the windshield for a very small fraction of a second while the poop took, in comparison, much more time.
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As stated by the calculations involving tensile strength, pressure is a factor. Since
pressure = (force)/ (area) , area is also a factor. The poop’s area was much less than a stone’s, unless the stone was shaped like a disc or flat sausage.
All said, I agree that thermal stress was the probable cause.
Listening to Wolfgang reminded me of my favorite physicist joke:
An egg farmer wanted to increase production, so he called in an engineer and a physicist for recommendations.
The engineer came back in a week with a plan for a high tech hen house. All functions would be automated including feeding and egg collection. Lighting would simulate day and night conditions to optimize egg laying, and soothing music would keep the hens contented. He predicted a 40% increase in productivity.
A month went by and the farmer still had not heard from the physicist, so he went to visit him at his office. He found the physicist at his desk pondering a sheet of paper in front of him, on which he had written, “Assume a spherical chicken.”
When Wolfgang said he assumed that the blob of bird poop was spherical, even though he knew that link sausage was a more accurate description of the shape, I almost drove off the road laughing.
Actually the Air Force a a launcher to test fighter plane windshields for bird strikes. They take whole chickens, feathers and all and freeze them solid. They are then launch at the windshield from a cannon. They freeze them because at the speed of a fighter, it is the same as if they were frozen even though they are when the soon to be dead bird was previously alive.
Have you ever seen a Great Blue Heron flying over? They are big, very big! In the 30’s, then because dad and his friends ran the creeks of western Pennsylvania they would get out of the way of these birds. Why, well when they let go of a poop you didn’t want to get hit by it. Hence, they named the bird a “shot poke”, why, well then they let go that poop was enough to fill a poke. So I imagine that could break a window easy… I would also think there would be evendence of the droppings at the scene of the incident.
GWG777, have you ever seen Great Blue Heron poop? It’s pretty much liquid poop.