http://scienceblogs.com/dotphysics/2010/06/collisions_kinetic_energy_or_m.php

Took the words right out of my mouth. Or right off my keyboard. Whatever. I’m just happy to see other people are considering the same questions.

But I’ve got a couple of things to add. First of all, kinetic energy can be easily related to momentum using the formula

which tells you directly that an object with the same energy but larger mass will have a larger momentum.

Also, the big question: is it energy or momentum that gives a collision its decapitating power? My thought is that it actually depends on force. Think about this from the point of view of a particle in the neck. This particle doesn’t “know” (as if a particle could “know” anything) how big the sheet of glass hitting it is; it doesn’t “know” how much energy or momentum the glass has. The reason is that energy and momentum are what I’m going to call global properties, basically meaning that the total amount of them possessed by some object comes from contributions from all different pieces of the object. To measure a global property of the …

More Mythbusters! Yayyy!

Just kidding, I am not that incessantly perky. But I did have an interesting thought while watching last week’s episode of Mythbusters. Kari, Tory, and Grant were testing the myth that a man in Germany launched himself 150 feet high using 400 firecrackers and splashed down safely in a lake. First of all, how dumb is this guy? Darwin Award anyone? (I guess he’d technically be ineligible since in the myth, he survived unharmed, but it was certainly a noble effort)

Anyway, here’s my physics thought of the week for last week: \(v = \sqrt{2gh}\). That’s the formula for the vertical velocity you need to reach a certain height as a ballistic projectile. To get 150 feet of altitude requires \(\unit{47}{\mileperhour}\), and that’s if you launch straight up. Coming off an angled ramp, as they did in the show, you’d have to be going even faster. Of course, the guy in the myth isn’t quite a ballistic projectile; he gets an extended boost from the rockets. But still, \(\unit{150}{\foot}\) of altitude is pushing it, so I would have been inclined (pun? intended? nah) to dismiss this …

Like everyone else, I feel a need to analyze the giant water slide in the latest Mythbusters episode. But honestly, there isn’t much left to say. The original video has been around for a while and everybody else who does this kind of analysis has already had the chance to do it. Example 1; example 2 (okay, so I’m only linking to one blog, but there must be more).

I guess I might as well do the obvious calculation, but I’ll use the Mythbusters’ parameters instead of those from the original video (which are unknown). The slide starts with a downward ramp \(\unit{165}{\foot}\) long at a \(\unit{24}{\degree}\) slope, which then curves upward to a \(\unit{30}{\degree}\) launch ramp that terminates \(\unit{12}{\foot}\) above the surface of the lake. They didn’t say how long the launch ramp is, but I can work without that information. I’ll be trying to calculate two quantities mentioned on the show: how far each Mythbuster flies from the end of the ramp, and his maximum speed.

(here’s a full-size version)

There are two parts to this problem:

1. The slide
2. The flight

The first part …

The news of Google’s Street View cars collecting WiFi data has been echoed around the internet for a while now. Now, obviously this is a Bad Thing that they shouldn’t have been doing, and there should have been internal checks in place to make sure it didn’t happen. Fine, I agree. But the fact that it did happen doesn’t make them evil, as a lot of people seem to be saying. According to the official blog entry at least (which I don’t have any particular reason to doubt), it was a mistake. Mistakes happen, and a large organization like Google is going to have a correspondingly large number of them.

Now, think about it from the perspective of the Google people. Once they found out this happened, they couldn’t go back in time and prevent it. The data had already been collected, the news had already been released. Under the circumstances, deleting the data and shutting down the WiFi scanning was pretty much all they could do. Rereading the blog post, it occurs to me that this is pretty much the kind of reaction I’d want to see from a company in their …

StackOverflow, and more generally the idea of a collaborative, community-moderated Q&A site, is a great invention, although I don’t quite share Jeff Atwood’s level of enthusiasm for it (or at least not his maniacal obsession with overthrowing the phpBB empire and conquering the universe of online information exchange). I mean, I don’t think it has that much of an advantage over the traditional web forum, especially given that since answers are editable and ordered by vote count (which changes frequently), it’s hard to hold and follow a discussion when just a simple “this is the answer” post doesn’t suffice.

But every once in a while, the StackOverflow model really gets a chance to shine. Take a look at this question about improving a Python function’s coding style. The top answer is a model of beautiful Python coding with iterators (well, in that peculiar sense of “beautiful” that only an experienced Python programmer can appreciate), but it didn’t start out that way. There were three of us who answered almost immediately, each making one or two little improvements to the code posted by the original questioner, and then over the next 15 minutes …

The blogosphere has been abuzz with analysis of last week’s episode of Mythbusters, in which they tested Jamie’s assertion (from a previous episode) that two cars crashing into each other at 50 miles per hour is the same as one hitting a wall at 100 miles per hour. OK, well, that turned out to be wrong.

I didn’t have the time to write about it just after the episode and there’s no point in me repeating what’s been said about it elsewhere, but I do want to point something out: the reason it was wrong is that in one case, a car crashes into another car, and in the other case, it crashes into a wall. The car and wall react differently in the collision — the car compresses, the wall doesn’t, so when there are two cars involved, the energy of the collision gets split between them. There isn’t any fundamental difference between two objects crashing together at 50 miles an hour and one object at 100 miles per hour crashing into a stationary one.

I would have liked to see the Mythbusters test one car at 100 miles per hour crashing into …