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NASA's Foam Test Offers Lesson in Kinetic Energy
Puneet submitted a followup story on the foam test that NASA conducted to get an idea of what sort of damage could be caused by foam falling off the shuttle fuel tank at launch. As it turns out: a lot.
Look to the left -- it looks a bit like a shadow. You can also see where the foam embedded itself in a T-seal.
Toronto-area transit rider? Rate your ride.
A more appropriate equation to invoke might be:
E=1/2mv^2
Kinetic energy on the scale involved can be nasty.
> F = Ma
It's not really force/acceleration that's important, it's kinetic energy and momentum:
Kinetic Energy = 0.5 * mass * (velocity^2)
Momentum = mass * velocity
So a 1g spec of dirt travelling at 20,000mph has the same momentum as a 1KG block travelling at 20mph - something best avoided!
Birds take down planes because they kill the engines. A bird hitting a 747 wing will just be obliterated.
Otherwise flying through heavy snow/rain would down every aircraft on earth.
Tom
Someday, I'll have a real sig.
They've talked about firing foam samples at wing mockups at hundreds/thousands of miles an hour, 'cause (I think) the Shuttle was flying at that speed when it was hit. But wasn't the foam also flying at that speed? Shouldn't the actual velocity of the foam hitting the wing edge be fairly minimal?
You are probably somewhat right, the velocity of impact is something like the speed of the shuttles ascent - speed of the foams ascent. However to maintain a 500 MPH ascent requires a considerable amount of constant energy. The foam probably decelerated much quicker than you are thinking.
The videos are here (where the panel visibly ripples after the impact) and here.
The accompanying slide presentation has the details: the 1.7 pound foam block was fired at 531 mph and, where it struck a T-seal between two panels, displaced them and caused a 4/10 inch gap. This fake wing was made of fiberglass, but given the results, a test with actual shuttle wing material from the Space Shuttle Discovery is planned for today.
Here are some of the headlines from news.google.com:
Shuttle Wing Under Gun
Investigator Amazed by Shuttle Foam Force
Foam theory faces pivotal test
Tests Show Foam Causing Wing of Shuttle to Deform
Foam chunk was shuttle's undoing, tests indicate
The article says he is the Director of NASA Ames research center, not that he *is* a rocket scientist. He is not a rocket scientist. His bio (http://www.arc.nasa.gov/about_ames/hubbard.html) from NASA shows him to be a long time administrator, with his original scientific background in radiation detection materials and devices.
So will people *PLEASE* quit insulting rocket scientists.
. there used to be a sig here.....
And that same 1KG block would have to be travelling at 632MPH to have the same kinetic energy!
K = 1/2m*v^2
K = 0.5 * 1g * 20000mph^2
K = 200000000
Therefore:
200000000=0.5 * 1000 * mph^2
40000 = mph^2
mph = sqrt(40000)
mph = 632.4555
Momentum increases artithmetically with velocity where as kinetic energy increase geometrically with velocity.
If VISTA is the answer, you didn't understand the question
But regardless, I believe the 500 mph was measured by looking at how far the foam moved between frames of video, relative to the shuttle.
I don't think it was calculated from an acceleration.
main(O){10<putchar((O--,102-((O&4)*16| (31&60>>5*(O&3)))))&&main(2+ O);}
LN2 is cool!
The exact values can be found in public record if you choose to look
The foam was moving 500 mph relative to the wing
But gravity is not the only force involved. The shuttle was moving up at 1000 miles an hour.... through the air and the wind. When the foam broke away, it immediately became subject to wind resistance, and slowed down due to wind. A 2 pound piece of foam in 1000 mile an hour wind can change velocity quite a lot in 200 feet. It was able to slow down (relative to the ground/wind) by 500 miles an hour due strictly to wind resistance.
The math is left as an excercise for the viewer.
There is nothing so silly as other peoples traditions, and nothing so sacred as our own.
Well, just doing some basic math, not accounting for friction etc, and assuming a constant upwards accelleration of 3G for the 81 seconds before the impact, you can see that:
a = 3g = 3 x 9.81 = 29.43 meters per second per second
v = at = 29.43 x 81 = 2,383.83 meters per second
= 8,581,788 meters per hour
= 5,332 miles per hour (approx)
So, the orbiter would have been travelling at around 5,300 miles per hour at time of impact (probably faster, since fuel and air drag would have been rapidly reducing, and therefore accelleration would have been gradually increasing).
When the foam seperated from the ET during the launch phase, at that speed, downward drag due to air resistance, and the relatively light mass of the foam section would have been significant - certainly enough to give it a relative velocity in the 500 - 1000 mile per hour range!
(Of course, it's been 8 years or so since I did Physics, so my assumpsions in those calcs may be way off, but I think you get the general idea!!!)
Disclaimer: I meant what I thought, not what I wrote! What? You can't read my Mind? Oh dear!
This is incorrect for several reasons. First of all you seem to be saying that acceleration is a vector quantity by making it bold, yet you do not bold force?
So now lets look at F=ma and see how it applies in this situation. Most idiots agree that F=ma is Newton's Second Law of Motion. Well they are wrong.
This equation does not work if the mass is changing. In rockets masses tend to change. So now lets look at the appropriate equation for Newton's Second Law.
F=dp/dt
This equation states that force is equal to the rate change of momentum. When the mass is not changing this becomes F=ma.
Finally none of these equations make a damn bit of sense if your not using the SI system. Less you forgot to include a gravitational constant or other English system mess.
Where does the .0379 come from???
/h = 222 m/s
Did you change 200ft into miles, when you already changed the shuttle speed?
Here's real math:
500 mph = 800 km
200 ft = 61 m
thus:
a = 403 m/s or 41 g
people, please check your units!!!!!!!!!!!!!
Almost. But you converted your 200 feet into miles -- which you weren't supposed to do. Using the correct numbers, you get (733^2)/400 = 1344 = about 42 g's. Since air resistance is proportional to a (very large) velocity, that doesn't seem too farfetched.
How can we continue to believe in a just universe and freedom to eat crackers if we have no ale?
At the time the foam fell off, the shuttle was still accelerating at full power. The piece of foam also entered the slipstream between the shuttle and the external tank, which is where most of the acceleration came from.
A bit of a blue-sky thought: but could they have potentially docked with the ISS?
Nope. By the time they realized that something *MIGHT* be wrong, they were already in the wrong orbit for ISS. There wasn't enough delta-v available to get to ISS.
Fascism starts when the efficiency of the government becomes more important than the rights of the people.
What's really funny (and what provides an additional clue that this is an urban legend that's been around the block a few times) is that in most versions of the legend, it is a group of American engineers who have to clue in their foreign counterparts (their nationality varies too) that they have to thaw the birds first. If there's one universal in comedy, though, it's making fun of foreigners.
"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
Finally none of these equations make a damn bit of sense if your not using the SI system.
Really? As I recall, the SI system didn't exist when Newton developed his equations.
Also, as long as you use the proper constants, what's the difference if you use kilograms, meters, and seconds; or slugs, feet, and seconds?
Fascism starts when the efficiency of the government becomes more important than the rights of the people.
Yes - but remember that the foam problems started when they switched to the CFC free foam, even thought they had an exemption.
Gotta be eco friendly
It was the shuttle's 1000 MPH speed relative to the ground that caused a 1000 MPH apparent wind relative to the shuttle, which blew the foam so that it was traveling 500 MPH relative to the shuttle. OK, clear?
The guy expressing 'shock', is an administrator. He is the chief at NASA Ames, where I work, and part of his job is to 'interface' with the public. That sometimes (often?) leads to statements that would make a scientifically minded person cringe. I expect these comments will be widely reported, and widley condemned as the NASA scientists being incompetant...
"It's overkill, of course. But you can never have too much overkill." - Anonymous Slashdot Coward
...since the slipstream is stressing the wings. Any analysis of the problem needs to take into account that the leading edges are under significant stress. This is why the SSME's are throttled back during the launch, to reduce the maximum loading on the airframe.
The insulating foam for the space shuttle that broke off and possibly destroyed the shuttle was a new formula since 1997 that has been problematic since it replaced a freon based foam. Although the freon-based foam worked better, the new foam was used instead rather than getting an exemption. So, if the foam is the root cause, it appears political correctness was more of a concern than using the best material for the job, possibly costing the lives in the process. Here's an article on the subject
Vote for Pedro
Define "more concentrated". Density of the two materials will not effect the force exerted on them if they have the same mass (unless the feathers are spread between here and low earth orbit.)
If a kilogram of bricks is put on a scale beside a kilogram of feathers on a scale, the readout from the two scales (aka, the weight) will be equal.
The metric system isn't silly with respect to mass and weight, it keeps them seperate. Kilograms are a unit of mass, and get used day to day because they more accurately reflect the common man's need for such a unit. People are generally interested in buying an AMOUNT of a material, instead of an AMOUNT THAT EXERTS A CERTAIN FORCE. Weight, on the other hand, is expressed in Newtons, and is generally used for scientific or engineering applications.
For example, if I bought a kilogram of sugar on the moon, I would be getting the same amount of sugar as if I had bought a kilogram of sugar on Earth. A pound of sugar on the moon would be five to six times as many granules of sugar as a pound of sugar on Earth, however.
I don't mean to sound like I'm flaming here or anything, but the popular confusion of mass and weight, especially in the Imperial unit system, really bothers me.
NASA designed a 'rescue ball' for just this contingency. It was never deployed. Personal Rescue Enclosure
--buck