Saturday, October 17, 2009

Falcon Heene, Balloon Boy



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.

Oh brother.


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  V=\pi r^{2} h
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 ---------






At this point I was done. This was a best case model of the balloon, being conservative on the weight of the child, the balloon frame and materials, and the volume as I knew it at the time. I was pretty darned convinced that the kid never was in the balloon as it could not have take off, and either the whole thing was a hoax, or the kid was scared and hiding for letting his daddy's balloon fly away.

I said as much to the older lady at the next table, and her reply?

"That is not what the news people say!"

Oh well.

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.

Friday, October 16, 2009

A Snowballs Chance (FPOTW)



I love snow! There is so much physics involved with snow. You can study thermodynamics, kinetics, optics, fluid dynamics, crystallography, solid state physics and statistical mechanics and still not know enough about snow. Quantum mechanics, chemistry…

There are some quick Fermi problem associated with snow:


--- Start Fermi Problem ---

  • Estimate how much snow falls over the Earth each year.

  • About how many snow flakes is this?

  • How many protons are in this amount of snow?

  • Estimate how much energy it would take to melt all that snow.

  • Estimate how much energy it would take to vaporize all that snow.

  • How many snow men could be made with all that snow?

  • If all that snow was turned into snowballs, and a great world war with snowballs were launched involving the entire planets human population, about how much energy would the people throwing the snowballs expend (neglect throwing each snowball more than once).
  • How long would the war last (assuming the snow does not melt first) ?

--- End Fermi Problem ---


War is hell, so what are the snowball’s chances?

Tuesday, October 13, 2009

Cool as Hell! (Or hot?)

Back in May I came across a wonderful picture of the transit of the Shuttle Atlantis and the HST across the sun, as captured by astrophotographer Thierry Legault.



The little dot you see in quadrant III is the space shuttle and the HST.

I wanted to post a quick little Fermi problem, even though it is not Friday yet:

Determine from the image the rough dimensions of the space shuttle.

Like any good Fermi problem, there seems to be too little information.
And perhaps there is.
So, you are allowed to use your Google-fu to determine how far away the sun is (about 8 light min) or the diameter of the sun. You can also use distance of the moon and recall that its angular diameter in the sky is about that of the sun (that is why we get such nice eclipses).
Perhaps you can look up some basic trig formulas?

There is not "right" way to do a Fermi problem, just way's that make sense.