I have got to learn to keep a pen handy with me at all times.
There are many times where I need to do a quick calculation, usually at a restaurant for some reason, and when I ask the server to borrow a pen they give me a wary look and act like I am going to steal their prized pen. Heaven help me if I ask for a piece of paper!
Thursday afternoon I was coming back home after a doctors appointment, and being hungry I decided to stop at one of my favorite restaurants, Pho 78 in Westminster near my home. I walk in,place my usual takeout order of Pho Tai, Chin, Nam, Gan and Sach (special characters omitted) with a yummy mango boba, and sit down to wait.
At this point I notice that everybody in the place is staring raptly at the wide screen TV mounted to the wall, on which an image of a silvery, flying saucer looking Mylar balloon is tumbling and spinning.
Captioned below is the usual "breaking news" and I saw that the event was taking place in Colorado. I assume this is a local news story, and curious, I start paying attention to the voice over:
"The boy may have fallen from the balloon... mumble mumble"
"Huh?" I eloquently think to myself.
I turn and ask an older woman sitting at the next table what is going on, and she responds: "What, you haven't heard? There is a little boy trapped in that balloon! Poor boy has been in there for hours and hours and must be scared to death!"
First thing I think to myself is "Shit! Poor kid... I hope he does not hit any power lines!"
Over the next 5 min I hear a constant babble about how old the kid is, how long he has been trapped, perhaps that he fell, and other sometimes contradictory statements. All this time I become more and more skeptical. Something was bothering me.
First, the balloon was acting very strange as it was tumbling, it looked like it had way to little inertia to have a 60 lb 6yo kid inside. Second, the balloon looked a bit too flimsy and small to hold the weight of the child.
Finally the news anchor gave the dimensions of the balloon, at which time I turned and asked the person behind the counter if I could borrow a pen.
I was scrutinized closely, and was handed a pen that was 10 inches long, an inch thick, and had a flower glued to the end.
I grabbed a paper takeout menu and began a quick and dirty estimation of the lifting capacity of a helium filled balloon.
------- Calculation section ---------
Density of air in Colorado ~ 1 kg/m^3
Density of Helium ~ 0.2 kg/m^3
So lifting capacity of Helium in Colorado is about 0.8 kg/m^3
The weight of a 6yo boy I estimated to be about 60 lb, and the weight of the Mylar and frame to be about 10 lb to be conservative. So a total weight of about 70 lb, or 32 kg.
~~~~ Short digression
At this time my pen ran out of ink. When I asked for another one the person behind the counter said: "What you do that pen? No more pen!"
I saw another one behind the counter top and after a while spent asking for it, she capitulated and loaned me the other pen, and I got back to work.
~~~~ End Short digression
Therefore the volume of the balloon needed to lift 32 kg was 40 m^3.
Next I assumed the balloon could be modeled as a disk of volume
Of course this assumption is not perfectly valid, as the balloon was not a perfect disk, and there was considerable uncertainty to the exact dimensions. Also, I did not consider leakage rate, or air resistance, or temperature rate with altitude etc. Assuming a disk is the best case scenario, and would over-estimate the volume, and was good enough for a quick and dirty
According to the news, the balloon was 20 feet in diameter, and 5 feet high. Turning the crank:
V ~ 3*(5 ft)*(10 ft)^2 = 1500 ft^3 ~ 42 m^3
--------- End Calculation ---------
I said as much to the older lady at the next table, and her reply?
"That is not what the news people say!"
At this time my order was ready, and I returned my pen (much to the relief of the owner I am sure) and went home to gorge on pho!
I say people should think over things critically, and they should. But I also can see why this is easier said than done.
People are protective of their young, and are concerned on the safety of other young people.
The media knows this, and knows they can sell papers, or draw viewers to advertisements if they concentrate on taking advantage of this tendency.
You see, even after I had left and gone home, I had been thinking this was a local news story. I do not watch broadcast TV, but instead I watch my shows online. I was tired, and coming down with the flu and went to bed after the pho, and it was not until the next morning on the drive to work that I found out that this had been an international story!
Thus is the power of media, and a prime example of why one should try and think critically of such news stories.
I cringe to think of the hours of productive work that were wasted by people watching this program. (Hey! I feel a Fermi problem coming on!)
Yes, remained concerned, but try not to get caught up in the hysteria pushed by the news. What the "news people say" has a high probability of not being correct.