How to Defeat Terrorists

I was having dinner with family and some good friends, one of whom is an engineer several scores my elder. One of the topics that came up was how engineers see the world differently. This can be a potentially prickly question, especially since engineers are often considered to lack adequate social skills.

I have always been a “glass is twice as big as it needs to be” kind of guy — neither optimistic nor pessimistic…things just are.

The Boston Marathon Bombing a month ago was a horribly tragic event. In the aftermath, I felt powerless. I was scared that I no longer had sufficient control or predictability in my life, that at any moment a bomb may go off and I would be the one killed.

As I let that sit, the conclusion my mind settled on is remembering that life is unpredictable. We can guess what will happen next with relatively good accuracy. And for everything else there is typically various forms of redundancy.

In the end, things just seem to work. Except when they don’t.

Redundancy provides a statistical reduction in probability of failure through investment. It could be considered a form of insurance since it’s a risk shift through payment.

Redundancy is not free, and may often go unused. Sometimes we misjudge the risk and bad things happen.

Bruce Schneier is one of my favorite authorities on system security and once again provides great insight:


It’d be easy to feel powerless and demand that our elected leaders do something — anything — to keep us safe.

It’d be easy, but it’d be wrong. We need to be angry and empathize with the victims without being scared. Our fears would play right into the perpetrators’ hands — and magnify the power of their victory for whichever goals whatever group behind this, still to be uncovered, has. We don’t have to be scared, and we’re not powerless. We actually have all the power here, and there’s one thing we can do to render terrorism ineffective: Refuse to be terrorized.

Empathize, but refuse to be terrorized. Instead, be indomitable — and support leaders who are as well. That’s how to defeat terrorists.

I disagree with Bruce on being scared, in my opinion feeling scared is valid, especially immediately after something like the Boston Marathon Bombing. What I believe Bruce is getting at is our long-term stance, and I agree that in the long-term we must choose not to be scared. We need to understand the bigger picture and choose to not be terrorized. Far to many of those whom we have elected (and continue to elect) are scared, even if they are only are only scared of losing their next election.

We must make better choices. We must choose to be indomitable. We must choose to support leaders who are not afraid. We must choose to make appropriate choices in the redundancy of our systems. We must not let the terrorist win.

What Keeps a Train on the Track?

At first, it may seem very simply and obvious: the flange keeps the wheel on the track, right?

Nope, that’s not the answer!

To understand why, let’s first get some background on how train wheels are made:

The primary take away from the above video is that train wheels are big and come together with a joined axle — that is, they don’t have a differential. If you don’t know what a differential is, or want to be impressed by an awesome video from 1937, take a look-see as this:

That still doesn’t explain what keeps a train on the track though. If you haven’t been able to figure it out yet, Feynman will explain:

…and that’s called rail adhesion.

via Kottke

Block and Tackle Efficiencies

Not long ago a friend was looking to upgrade the mainstay1 block and tackle system on his sailboat.

Mainsheet Upgrade

The question was if the proposed system would provide the anticipated reduction in force. It was an interesting question that, while seemingly straight forward, does have a couple of gotchas.

Block (pulley) and tackle (rope) calculations are usually pretty simple, with the mechanical advantage (MA) idealized as:

MA = \frac{F_B}{F_A} = n

where FA is the input force, FB is the load, and n rope sections.

Calculating the total force of multiple non-colocated blocks using the same tackle presented a fun challenge that requires one to take into account the individual location of the blocks and the forces transfered.

I did not draw every single link of the block and tackle, but in general the problem looks something like this:


Considering the moment arm:

F_{L} = (F_{A} \times A) + (F_{B} \times B)

We devise these relations:

F_{A} = n_{AD} \times F_{P} \times \arctan\left ( \frac{\left |  A-D \right |}{h}\right )


F_{B} = n_{BC} \times F_{P} \times \arctan\left ( \frac{\left |B-C\right |}{h}\right ) + n_{BD} \times F_{P} \times \arctan\left ( \frac{\left |B-D\right |}{h}\right )

where nxy is the mechanical advantage coefficient at a given point, x, with respect to another point, y; FP is the force exerted on the tackle (which must be uniform throughout!).

Using some assumptions regarding the lengths and relative positions of the blocks greatly simplifies the calculations, and we can plug ‘n chug from there:

F_{L}=F_{P}\cdot \left ( \frac{n_{AD}}{2} + \frac{n_{BC}}{4} + \frac{n_{BD}}{4}\right )\cdot \cos{(\arctan(\frac{l}{8h}))}

As expected, there is a loss of useful force due to the ropes not being normal to the boom and that causes the boom height/length ratio to become an interesting variable in these calculations. You lose 10% of your power with a 1:3.87 ratio, 25% with a 1:7.06 ratio, and 50% with a 1:13.86 ratio.

To model a direct input (with no block and tackle), I assume that the force was applied at a point between the two blocks, A and B, and normal to the boom.

The increase from no block and tackle system to the current system (single boom aft block, A; double boom traveling block, B) is:

\frac{F_{P}\cdot \left ( \frac{2}{2} + \frac{2}{4} + \frac{2}{4}\right )\cdot \cos{(\arctan(\frac{l}{8}))}}{\frac{3\cdot F_{P}}{8}} = \frac{16}{3}\cdot \cos{(\arctan(\frac{l}{8h}))}

…assuming the boom heigh/length ratio is 7, the mechanical advantage is 1:4.01.

Moving from no block and tackle to the the proposed system (double boom aft block, A; triple boom traveling block, B) is:

\frac{F_{P}\cdot \left ( \frac{4}{2} + \frac{3}{4} + \frac{3}{4}\right )\cdot \cos{(\arctan(\frac{l}{8}))}}{\frac{3\cdot F_{P}}{8}} = \frac{28}{3}\cdot \cos{(\arctan(\frac{l}{8h}))}

…again, assuming the boom heigh/length ratio is 7, the mechanical advantage is now 1:7.02.

The mechanical advantage from current system to proposed system is: 1:1.75

\frac{F_{P}\cdot \left ( \frac{4}{2} + \frac{3}{4} + \frac{3}{4}\right )\cdot \cos{(\arctan(\frac{l}{8h}))}}{F_{P}\cdot \left ( \frac{2}{2} + \frac{2}{4} + \frac{2}{4}\right )\cdot \cos{(\arctan(\frac{l}{8h}))}} = \frac{3.5}{2} =  1:1.75

It’s not quite the 1:2 advantage originally thought, but it’s close.


The bonus gotcha occurred when said friend opted to install a double boom aft block (A) and a triple deck traveler block (D), but keep the boom traveler block (B) as a double. Essentially, putting an extra “loop” just between the boom aft block (A) and deck traveler block (D).

The imbalance of tension on the deck traveler block caused it to experience shear stress and bind on the traveler rail in ways it was not designed to — not good.

Converting the boom traveler block (B) to a triple and the deck traveler block (D) to a quad equalized the tension.

Problem solved.

  1. rope from the top of the main-mast to the foot of the fore-mast on a sailing ship 

(NBA) Kings Won’t Build Their Own Castle

I will admit that, in general, I’m not a huge basketball fan. I know how to play, I know the rules, and I do sometimes enjoy watching it from time to time, but I couldn’t tell you the last time I’ve been to a game and I’ve never been to an NBA game1.

Would I like to have another NBA team in Seattle? Sure…it could be fun; but I don’t need them.

Do I want to provide them a financial incentive to come here, such as building them a new stadium with taxpayer dollars? Absolutely not.

The NBA may be “non-profit”, but the Sacramento Kings Limited Partnership2the basketball team — is most definitely for-profit.

This has been one of the biggest the issue I have with professional sports: NBA, MLB, NFL, etc: why should we, as tax payers, pay for a fully furnished building for a for-profit company?

In my opinion, we should not.

Daniels Real Estate of Seattle and equity partner Stockbridge Capital Partners are building a $400 million, 660-foot skyscraper in downtown Seattle: The Fifth and Columbia Tower. They didn’t need to secure financing or public support — they raised the money themselves.

And that should be the lesson from all of this for basketball in Seattle: If the market is truly profitable, then a company should be able to secure funding privately.

That’s what Chris Hansen, et al, have done. It’s not a perfectly privately financed deal, still financed by the public in part, yet significantly better than previous arrangements sports teams have been making with cities in the recent past.

And this same reason, using private funds to build a new stadium, also appears to be why the NBA Relocation Committee voted unanimously to veto moving the Kings to Seattle:


You see, in addition to offering $365 million for the team [which is $35 million more than the next highest bidder], the Seattle bidders were offering to build a brand new arena for the Kings. By contrast, the Sacramento bidders managed to persuade the city of Sacramento to build a brand new arena for the Kings. The Seattle bid, in other words, would have set a good precedent for the future of American public policy. And the owners didn’t want that. The owners want to be able to make this move over and over again. “Give us a new publicly financed stadium or we’ll move to Seattle” is a threat that works as well in Portland or Milwaukee or Minneapolis or Salt Lake City or Memphis or New Orleans or Phoenix as it does in Sacramento. And the major American sports leagues are organized as a cartel for a reason. An individual owner just wants to sell to the highest bidder. But the league approval process means the owners as a whole can think of the interests of the overall cartel, and those interests very much include a strong interest in maintaining the ability to get cities to pony up subsidies.

At the end of the day, the NBA will do what it pleases; and that’s how things sometimes go when people have free choice. Like I said, it could be fun; but I don’t need an NBA team in Seattle.

But if we capitulate to the NBA on who pays for the arena, that makes us only one thing: suckers.

Title shamelessly ripped from: One Foot Tsunami.

  1. as far as I can recall 

  2. California Business Entity Number: 199206300016