« That Goddamn Bell Couldn’t Save Everyone | Main | The Daily Memo - 6/1/06 »
Janie’s Got a Gun
Anyone who’s taken high school or freshman physics has probably encountered the example of a bullet being shot into a hanging piece of wood. By knowing how much the block moves after being impacted by the bullet, you can figure out how fast the bullet, itself, was traveling. It’s a great real world example of basic mechanics, inertia and the conservation of momentum at play.* Recognizing this, a Marin County teacher has taken it a step further, and for almost 15 years has been conducting a real life version of this experiment in his classroom.
Back in 1992, the former military police officer decided to use his Korean War era rifle to conduct this experiment and, after checking with the then-principal, it was decided that there was nothing wrong or illegal with the experiment and he’s been doing it ever since (in recent years, he has received written consent from the current high school principal). But when an anonymous parent found out about the experiment and complained, things got a little ugly since it’s apparently a felony to bring a loaded rifle into school without the written permission of the superintendent, and the superintendent knew nothing about this experiment.
Some decry the experiment as being “absolute madness” and “crazy in concept, [and] in light of the world we live in it is absolutely irresponsible.” Others, such as the current principal, recognize that this is something with “educational value,” providing “an interesting and dramatic example of physics in action.” The teacher himself says that, unsurprisingly, his students have always loved the experiment, and he takes every precaution to ensure that they are safe from any accidents or ricochets.
Seems to me that the right thing to do here is for the superintendent to simply provide written permission to allow the experiment to continue, as it sounds like they would then be in compliance with the relevant law. It sounds like the teacher is treating this with the proper amount of diligence and safety, which means the end result is nothing more than getting kids a little excited about physics. Considering how often folks cry (rightly so) about the fact that America is falling behind in the maths and sciences (W even mentioned it in a recent State of the Union address, if I recall correctly), we should be striving to find more experiments like this, things to get kids excited about science. If we just rely on the same old dry and stuffy classroom lectures, the science gap is only going to increase.
I have no joke or punch line for this entry because if we don’t fix this downward trend, at the end of the day the joke will be on us.
*For those who are curious, here’s my recollection of the physics behind this experiment (with the caveat that it’s been about 9 years since I’ve done any practical physics, even of such a basic nature). When you’re dealing with two objects which collide, like the bullet and the block, the law of conservation of momentum says that whatever momentum there was before the collision, there must be equal momentum after the collision. Now the momentum of any objection is just its velocity times its mass. So before the collision the bullet’s momentum equals its mass (call it little “m”) times its velocity (call it little “v”). The wood block’s momentum, before the collision, is similarly it’s mass (call it big “M”) times its velocity - but since it’s velocity is zero, it’s momementum is also zero. Now after the collision, the block and the bullet are essentially one, since the bullet is lodged in the block. So that momentum is the mass of both the bullet and the block (that is, little “m” plus big “M”) times the velocity of the block (call it big “V”).
All the momentum before the collision (the bullet’s “m” time “v” and the block’s 0) has to equal the momementum after the collision (the combined “m+M” times “V”). So we get a nice little equation that says: mv + 0 = (m + M)V. Which means that the bullet’s velocity, little “v” is simply: v = (m + M)V/m. We can measure the little “m” by weighing the bullet, we can measure the big “M” by weighing the block, and we can measure the big “V” by figuring out how fast the block moved. And once you know that, you can plug the numbers in and find out how fast the bullet was originally going. Physics!
Comments
Of course, this experiment is contingent on using block of wood thick enough for the bullet to lodge into and/or a bullet that does not travel fast enough to just go straight through the block, otherwise all you get is a bullet that was slightly slowed by its impact with the wood with only a split second's worth of momentum transferred. (For those of you who are just aching to try this at home, keep this in mind...and maybe use Magsafe or Glazer safety rounds.)
Posted by megaera | June 1, 2006 12:50 PM
You might also note a story in the June issue of Wired magazine, which relates to lawsuit-silliness and the inability to make chemistry sets. They decry the same loss of science interest as you do.
Interestingly, they talk to Don Herbert ("Mr Wizard") and find that his old kids' chemistry set would be largely unsaleable today. So pathetic.
http://www.wired.com/wired/archive/14.06/chemistry.html
Author's Note: Yeah, I actually meant to include a reference to that article in my little rant, and simply forgot. I can appreciate the need for cutting down on garage/trailer meth-labs and what-not, but they seem to be carrying things a little far here, failing to offer any sort of balance.
Posted by Kris Sargent | June 2, 2006 9:22 AM
As this is a website related to interpretation of the law, I am a bit confused. Either the experiment was legal or it was not. The boy suspended for having a kitchen knife in the back seat of his car after performing an errand, is not molified by reading your account.
A teacher brings a bomb to school to demonstrate conservation of energy. The principal allows it, with the assumption that the teacher was a saper or his father defused bombs. No military record is available, as with this teacher.
The principal does not know a joule from a jewel. As in this case.
A web consensus is that this teacher is creative. We all made bombs. We miss bombs. We love bombs. There would be more physicists if there were more bombs in the classroom. America would catch up to the rest of the world if there was a bomb in every classroom, to get the attention of the students.
How about, how big was the bomb? Was it handled safely? Didn't the law require the superintendent or his designee to ok the experiment? A designee is not the default person present. It is an affirmative action of appointment of an individual to fill a role in the absence of the superintendent.
I am sure no investigation was performed for safety, for fear of liability. No written approval exists from the principal. The superintendent did not know.
If after investigation, it is determined that this experiment is safe,it should continue. Either the law has been violated or it has not. Is the public entitled to a formal opinion, after a ballisics expert has reviewed the experiment.
I thought the purpose of the judiciary was to determine what is legal.
Do you want your local principal deciding what armaments make it into class? What about the sixth grade? Do you fire your 30 caliber weapons indoors, where they are capable of penitrating through walls and injuring someone on the other side? Where are the opinions of lawyers?
Author's Note: Your point is addressed, sort of, in my statement that: "Seems to me that the right thing to do here is for the superintendent to simply provide written permission to allow the experiment to continue." In other words, sure, the teacher was not complying with the proper laws and policies as they stand now, but that can be rectified by getting the superintendent to sign off on the experiment (after he makes a safety determination, which, per the language of the law, is his decision to make, not the judiciary's - ).
Posted by Gell-Mann | June 4, 2006 10:42 PM