Saturday, August 8, 2009

Ageing Gracefully

Dr. Crazy recently blogged about her impending birthday, so it is worth noting an interesting article about a study that shows that people get happier as they age.

The main lesson was summed up as follows:

They found older adults generally make the best of the time they have left and have learned to avoid situations that make them feel sad or stressed.

Now there is a good principle to hold in mind as we start a new semester! It also seems to summarize my parent's approach to a long and happy retirement. Some of it certainly results from living through the death of many old and dear friends and family. The start is to spend your time like the valuable capital it is. Don't let someone else spend it for you.

So .... is there someone out there whose goal in life is to annoy you until he gets what he wants (often an unearned grade)? Refuse to play the game. Demanding e-mail? Answer it on a set schedule - your schedule. We can choose to enjoy what we do and make 09-10 a good school year.

I'm ready. Literally and figuratively. I even have my first-week concept picked out, evolved from the old "critical reading" discussions, to see if I can repair the weak foundations they have with setting up problems (starting with reading them, before they show up as problems with actual physics problems. Should be fun for everyone.

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Wednesday, August 5, 2009

The Stimulus is Working

If all politics is local, so is much of economics. This picture is worth 1000 words.

Thanks to the $8,000 first-time buyer tax credit, the house across the street has sold after being vacant for more than a year. Better yet, the house next to it has also sold after also sitting vacant for more than a year. Both were sold to young, first-time home buyers who could use help with a downpayment but could move quickly because they did not have to sell a house to make the move.

Even better, my parents home finally sold after being empty for about 18 months. It also was bought by a first-time buyer. Like the two cases on our street, the seller cut the price significantly to get rid of the property, having long since moved to another place with its own expenses, so this does not signify any recovery in the price part of the market - but it has meant work for roofers, maintenance people, surveyors, and actual real income for realtors.

Along with one other sale about a block away, all of the properties up for sale in our immediate neighborhood are "gone" - and none of them were converted to rentals. That last part is a double bonus of the stimulus plan. With prices down, people with cash can pick up potential rental properties at a song. (One house on my drive to work went from "sold" to "for rent" in one day, but it is closer to the colleges.) This plan puts an owner in the house, which is a big plus for everyone around us.

So this part of the stimulus bill is working well. The only difference between it and the "cash for clunkers" program is that it isn't using appropriated dollars so there is nothing for the Republicans to complain about yet. It remains to be seen if they will complain about having to subsidize a TAX CUT for new homebuyers in the same way they criticize a rebate for people replacing a 14 mpg truck (SUV) with a 28 mpg car that will cut each individual's demand for foreign oil in half!

Any bets?

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Sunday, August 2, 2009

A View of America

There was a very interesting column from BBC World News today. Their American Correspondent is ending an 8-year stay in this country, and writes his thoughts about America, from how we approach buying a home to a rural road in South Carolina to his view that our "anyone can get ahead" worldview is closely tied to our "carelessness" (i.e. lack of a Nanny State). Liberty is, after all, necessary for someone from the lower classes to move into the upper classes even if it also lets parents refuse to treat their child's disease.

I thought the one thing he missed was that the sub-prime mortgage crisis only brought down the rest of the world's economies because they were as greedy as we were (the exception being China, who only buys government paper), and that the housing bubble was not much different from other scams that helped create this country, including ones that brought the first settlers here.

In what is actually a related story, Raul Castro says he is not going to "reform" Cuba into a capitalist country. That's OK, it will become one as soon as the South Florida Cubans get over the fall of THEIR dictator and realize that the fastest way to bring down the Castro system is to let people visit there and spend money. That won't prop up the government, it will destroy it, one iPod at a time.

As Fareed Zakaria puts it in his book on illiberal "democracies", first security, then middle-class incomes, then democracy. China is well on its way down this path, whereas Russia (and the many failed democracies of the post-colonial era of my youth) failed because the people were too poor. That was the most fascinating bit of statistical politics in the entire book. Our isolation of Cuba, originally at the behest of former Batista allies, is keeping the Castro family in power!

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Racing Helmets

The problem is not that of a standard inelastic collision, yet that is the essence of the problem: how to dissipate energy while conserving momentum, and how to reduce the acceleration of the head inside the helmet when the impulse being applied is not under your control. Complicating this is the need to keep the weight of the helmet down so that the helmet itself does not cause injury by increasing the forces on the neck in a crash (the problem that the HANS device helps solve as part of a coordinated systems approach to safety). More on the physics at the bottom of this article.

There is an excellent story on the Formula 1 website about the evolution of racing helmets, driven by the amazing survival of Felipe Massa after being hit in the helmet by a 1 kg spring that came off of Barrichello's car (at a closing speed of about 160 mph), although it doesn't give much credit where it is really due over the history of motorsport. The helmet they show Fangio wearing, which originated for use when playing polo, was similar to the one worn in a key death in the US that started the move toward today's safer helmets.

It was the Sports Car Club of America that was the first to require seat belts in automobile competition (1954), and it was an SCCA member who started the Snell Memorial Foundation in 1957 to provide testing for helmets used for automobile racing after the death of Pete Snell in a racing incident. Their page about the history of the organization and its current activities shows the crash that killed Pete Snell, discusses the physics of a crash, and shows the sort of testing that goes into certifying a helmet. The photo at the very bottom of this page shows a sample drop test of a helmet that tests for the sort of thing that happened to Massa.

The Massa incident was as close as it gets. Getting hit in the head by 1 kg spring at a relative velocity of about 160 mph would be fatal without a helmet even when the spring was deflected by the nose of the car and the bolster on the side of the cockpit. Even the helmet was put to the ultimate test, because the impact point was at the edge of the opening. You can see the effect in the AP photo that accompanies this news article. Higher resolution images of just his helmet and eye injury are available if you search "massa crash" on google images, but I don't recommend doing so.

The Physics

Some things about the collision of an object with a helmet are outside your control. The momentum of the incoming object is a given. The amount of momentum transferred to your head and helmet is somewhat under your control, but mostly depends on things like the angle of impact that you really can't do much about. Bouncing off (elastic collision) makes the momentum transfer worse for your head, so design can help a bit, but physics puts a lower limit on what engineering can do about this part of the problem.

The amount of momentum transferred to the helmet is what is called "impulse". You can reduce injury if the helmet or its lining is soft enough to increase the duration of the collision, thereby reducing the force applied to the head. This is also the job of seat belts and other safety systems, but only a helmet can protect you against the impact of an object or the road itself.

BTW, there isn't much that a helmet can do if something large (like a wheel) hits you at high speed. There are things that will kill you in motorsport. Based on one of Hemingway's rules, that is what makes car racing a sport. (If there is no chance that the animal you are hunting can kill you, he did not consider it a sport.)

The helmet has to provide an artificial skull, to protect your skull. (That means it has to be hard and strong, so it is the job of the lining to dissipate energy.) Even though the impact was right at the edge of the "eye socket", the helmet Massa was wearing did an amazing job. It appears that fragments from the helmet or visor injured his eye, although the damage could also result from a fracture as the helmet hit his head. That is the other thing the helmet has to do: absorb energy and redistribute the forces over the entire head. Massa's helmet just barely managed perform that task. He still had a fractured skull as well as a concussion from the forces that were applied to his head by the helmet.

Apparently he also had a fracture at the base of the skull (what killed Dale Earnhardt), which is supposed to be less likely with a HANS device. His roughly 120 mph impact with the tire barrier should not have produced this, as I understand the designs, so that might also have resulted from an unanticipated motion of the helmet from the spring impact. It also makes me worry about how the emergency people were moving him in the news photo I link to above!

And just to be clear:
Physics is not the entire story. Physics tells you the constraints of the problem. It tells you what physical principles apply and what forces MUST result from those principles under specified conditions. Engineering is the task of choosing materials that will handle those forces and dissipate energy without adding too much weight, so the forces that get to the head are within limits known from the analysis of deaths and injuries from past crashes. More will be learned from this one.

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