Saturday, December 10, 2011

Weekend post - The physics of road safety

I’m a little obsessed by road safety at the moment. This is partially because a very good friend of mine, a loving and vibrant young wife and mother, was killed a few weeks ago in a car accident. It’s also because I’m a driver. I spend up to 2 hours each weekday behind the wheel of a car, driving mainly around Gaborone. You can’t do that without spending much of the day considering matters of mental health. How did that combi driver not see me in my great big car or perhaps he just didn’t care? Why did that BX driver think it was acceptable to overtake in the face of oncoming traffic, crossing a solid white line and exceeding the speed limit? How did that person ever get a driving licence?

As well as questioning the mental health of drivers I often find myself wondering whether drivers studied any science at school. Don’t they know anything at all about physics?

Newton’s First Law of Motion says that the velocity of an object will remain constant unless a force acts upon it. The cup of tea on your desk isn’t going to move unless you pick it up. The ball you throw in the air will only change direction and speed because of air resistance and gravity. A passenger in a car will continue moving in a straight line within the car when the car hits a brick wall. If a car travelling at 60 km/h hits a solid object and suddenly stops the occupants will continue moving at 60km/h until something stops them as well. If they’re lucky it’ll be their seatbelt or an airbag that will slow them down as gradually as possible. However if they’re not stopped by something soft it’s likely to be something very hard indeed that does it. Something like the steering wheel, the windscreen or the wall the car hit after they’ve burst through the windscreen in a spray of blood and bone.

Let’s take a simple, not too scary example. Imagine a child is in the front seat of a car that’s just left your house. Let’s say it’s a perfectly average 9-year old girl who weighs 30kg. She’s not strapped in. The car is travelling slowly at only 30 km/h but collides with the back of a massive truck and stops almost instantly. Let’s say it takes a meter to come to a halt. In the 8th of a second the car takes to stop the girl becomes a flying object within the car. She’ll hit the windscreen at something close to 30 km/h with a force equivalent to a man weighing 117kg jumping on her. She’ll probably live.

The problem is that this isn’t typical. Who drives at 30 km/h? The other problem is that the amount of energy a moving object possesses is not directly related to it’s speed. The kinetic energy of an object is proportional to the square of its speed. Double the speed and you quadruple the energy. To make matters worse if you double your speed you don’t necessarily double your stopping distance. If the car driving that unrestrained little 9-year old girl hits the same truck while travelling twice as fast, at 60 km/h, it’ll probably still stop in a metre. This time she’ll hit the windscreen with a force of almost half a ton. She’ll probably die.

Let’s be completely depressing and double the speed again to 120 km/h. The same collision will hit her with a force of almost 2 tons. She won’t just die. Someone will be forced to reassemble her body so a relative can formally identify her. I know a very brave uncle who volunteered to identify the pieces of his niece’s body so his brother, the girl’s father, didn’t have to. He couldn’t bring himself to drive his car for weeks afterwards. Every time he got behind the wheel of his car he was plagued with the images from the morgue.

That’s why I lose my temper when I see loving parents driving their beautiful children to and from school each day and they allow their kids to stand up on the front passenger’s seat. I get even madder when I see an unbelted adult in that seat with a kid on their lap. You know what? It might not just be the windscreen that kills her, it’ll be your body hitting her from behind, crushing her from front and back. Could you live with the knowledge that your body, perhaps the body that brought that child into the world, is the thing that crushed her to death?

Maybe that’s what we need to teach in physics classes in schools. Instead of balls hitting each other or weights going up and down inclines we should use the idea of a little girl inside a metal box being driven by a psychopath. Maybe that’s the sort of science we need to cut down the slaughter on our roads.


For a quick summary of Newton's Laws of Motion see the Wikipedia page here. There's also a good explanation of the physics of car crashes here.

I'd like to say that I did all the maths in this piece myself but that would be lying. I did SOME of it myself but then was lazy and used the online car crash impact calculator here.

Saturday, December 03, 2011

Weekend Post - Is my laptop frying my fertility?”

The answer is almost certainly not but from the recent press coverage you can be forgiven for thinking otherwise.

The BBC published a story that was widely circulated that was headlined “Scientists question if wi-fi laptops can damage sperm”. The story reported that after being placed next to a laptop that was downloading data “sperm were less able to swim and had changes in the genetic code that they carry.”

Needless to say the headlines grew more and more scary as the story spread around the world’s media. The particularly hysterical British Daily Mail stated that “Radiation from WiFi connections can reduce sperm activity in up to a quarter of men” and the even more hysterical Huffington Post stated that “Wi-Fi Laptops 'Kill' Sperm”.

Unfortunately not all of the reports actually explained what the experiment involved and gave ment enough information on what to do with their laptops (and their laps).

The facts are a bit less scary that the excitable elements of the press suggest. To begin with this was just what the researchers called a “Prospective in vitro study”. This was just an experiment they conducted in a laboratory, “in vitro”, in glass. The experiment was actually very simple. Samples of healthy sperm were placed for four hours next to a laptop computer that was downloading data. Another set of samples was placed in an identical setting except there was no laptop downloading next to it. When they examined the samples after the four hours they discovered that the samples near the downloading laptop were less mobile and more damaged than the control group.

This was hardly real life. It’s certainly not what most men do with their sperm. Nevertheless it’s still an interesting study that it would be foolish to ignore. As the researchers say, “Further in vitro and in vivo studies are needed” to establish whether this effect is genuine. An “in vivo” study means a test in real life, in a living body. If other researchers can replicate these results an experiment with real men and laptops can be undertaken.

Until then we can be cautious. The most important thing is not to panic. The experiment these guys undertook is nothing like the normal way that men and women make babies. It’s also certainly not the way men usually offer their contribution to the baby-making process.

This was just one study, with a very small sample size, involving only 29 sperm samples and the effect was small. There is also no plausible explanation for how this effect might have been caused by the wi-fi network. The strength of a wi-fi signal is so weak that it’s unclear how it might have caused the damage. Critically wi-fi signals, like cellphone signals are non-ionizing, they simply don’t have the strength or frequency to cause damage to biological cells. They’re not like X-Rays or gamma rays that can have a massive impact on the human body. They’re not very different to sitting still while listening to the radio. The signals from your local radio station are around us all the time and nobody panics about them, do they?

However one thing that is known to affect sperm is heat. Excess heat around those parts of a man’s body can reduce fertility but the researchers in this study apparently ruled that out as an explanation. I’d find it perfectly easy to believe that repeatedly resting a laptop on your lap for a long period could effect a man’s fertility. Also sperm are fairly fragile and can quite easily be affected by a range of factors other than heat.

The BBC asked an expert, Dr Allan Pacey, senior lecturer in andrology at the University of Sheffield, for his reaction to the study. He said that “we cannot infer from this study that because a man might use a laptop with wi-fi on his lap for more than four hours then his sperm will necessarily be damaged and he will be less fertile.” That sounds sensible to me. Let’s wait and see what further studies come up with before banning wi-fi networks from anywhere near prospective fathers.

In the meantime, if you’re a guy worried about his fertility then not keeping a hot laptop on your lap for too long is probably very good advice. More importantly it’s hardly the way to woo your partner, is it? Better still, try some romance, you’re much more likely to make a baby that way, it’s scientifically proven. Trust me.


The original story from the BBC can be seen here and the abstract of the study can be seen on the Fertility and Sterility site here.

For the more hysterical coverage see the Daily Mail here ("Working on a laptop wirelessly may hamper a man’s chances of fatherhood") and the Huffington Post here ("Wi-Fi Laptops 'Kill' Sperm").

For more reasoned coverage see The Register here and Time here.

Killer bananas

It’s a fantastic plot for a science fiction, don’t you think? “Revenge of the killer bananas!” However if you believe some people the risk is real.

Like many others I received an email a few days ago that began:

“Do not eat bananas until further notice. PNP will investigate if there is any truth in this, but rather be safe.”

The email then explained the danger posed by these homicidal fruit.
“Please don't eat bananas for the next 3 weeks. Several deliveries of bananas from Uvongo Kwa-Zulu Natal South Africa have been infected with necrotizing fasciitis, otherwise known as flesh eating bacteria. Recently this disease has decimated the monkey population in the south coast. We are now just learning that the disease has been able to graft itself to the skin of fruits in the region, most notably the banana which is one of South Africa’s largest exports. Until this finding scientists were not sure how the infection was being transmitted. It is advised not to purchase bananas for the next three weeks!!!”
The email continued to explain how the FDA hasn’t issued a warning because it fears “a nationwide panic”. It also said that if you have an infected wound and are far from medical attention “burning the flesh ahead of the infected area is advised to help slow the spread of the infection.”

Are you feeling scared yet? Or just skeptical?

To begin with there’s a minor technicality. The FDA is a US body, not South African. Then there’s the “science” part of it. Let’s be honest about one thing. You do NOT want to develop necrotizing fasciitis. It’s a horrible bacterial infection that causes massive irreversible tissue damage and often results in either amputation of the infected body part or death. If you want to see some scary pictures do a web search but don’t do this while eating. However, can you actually catch necrotizing fasciitis from the skin of a banana?

No. The Centre for Disease Control in the USA says that there “is no evidence that necrotizing fasciitis is transmitted by food. The bacteria which most commonly cause necrotizing fasciitis live in the human body. The usual route of transmission for these bacteria is from person to person.” There is also little sense in the statement about the “disease has been able to graft itself to the skin of fruits”.

This story is a hoax. In fact it’s a very old hoax. This has been circulating around the internet for at least 12 years. It was first seen in 1999 but with a slight difference. That time it mentioned Costa Rica, not South Africa but the words in the email were otherwise exactly the same.

You can rest assured that eating bananas is still safe and they’re still good for you. You’re not going to be turned into a zombie by eating them.

However, what I find just as interesting is why people continue to send these emails. I know of several people who’ve received it and a couple who forwarded it to others. I know of one person who even posted it on Facebook. I’m sure all of these people were perfectly well-meaning and genuinely felt it was important to warn their friends about a possible risk but did they really believe the story or were they so shocked and horrified that they felt it was an emergency?

Or are they perhaps just a bit more suggestible than others? A bit less naturally skeptical? Psychologists have certainly identified that there is a scale of suggestibility with some people being more prone than others to believe what they see and hear. They are much more susceptible to suggestion, particularly with things like hypnosis but I suspect they’re just as susceptible with anything new, like emails about bananas.

I sometimes think that I’ve become overly skeptical at times, automatically assuming that something is not true until it’s proven to be so, But then I remind myself that I think this is by far the safest approach to take to life. Isn’t it better to assume what scientists call the “null hypothesis”, that something is NOT true until there’s a good reason to change your mind? That certainly goes for anything you receive in your email inbox and anything that makes remarkable claims. Sa Carl Sagan said, “remarkable claims require remarkable evidence”. There’s nothing remarkable about the killer bananas story other than the fact that people believe it.


Snopes has a report of the original hoax email that referred to Costa Rica here. There are several useful links at the end of the article. The Skeptic Detective has a comprehensive piece on the hoax here.

The official Centre for Disease Control statement can be seen here and there's a very assertive statement from the Kwa-Zulu Natal Banana Association (I SO want to join!) here.

If you're feeling brave and want to learn more about necrotizing fasciltis you can see the Wikipedia page here which includes a fascinating but ghastly fact about the death of King Herod.

The full text of the email I received is as follows:
"Please don't eat bananas for the next 3 weeks

Several deliveries of bananas from Uvongo Kwa-Zulu Natal South Africa have been infected with necrotizing fasciitis, otherwise known as flesh eating bacteria. Recently this disease has decimated the monkey population in the south coast. We are now just learning that the disease has been able to graft itself to the skin of fruits in the region, most notably the banana which is one of south africa ’s largest exports. Until this finding scientists were not sure how the infection was being transmitted. It is advised not to purchase bananas for the next three weeks!!! If you have eaten a banana in the last 2-3 days and come down with a fever followed by a skin infection seek MEDICAL ATTENTION!!!The skin infection from necrotizing fasciitis is very painful and eats two to three centimeters of flesh per hour. Amputation is likely, death is possible.. If you are more than an hour from a medical center burning the flesh ahead of the infected area is advised to help slow the spread of the infection. The FDA has been reluctant to issue a country wide warning because of fear of a nationwide panic. They have secretly admitted that they feel upwards of 15,000 South Africans will be affected by this but that these are" Acceptable numbers". Please forward this to as many of people you care about as possible as we do not feel 15,000 people is an acceptable number."

Thursday, December 01, 2011

This is how statistics should be portrayed.