Why Can't Elephants Jump?: And 101 Other Tantalising Science Questions - New Scientist (2010)
Chapter 7. Troublesome transport
Wheels of death
I heard that the car is the deadliest weapon created by humans and that the number of lives it has claimed exceeds the death toll from atomic weapons, guns or bombing. Is this true? And what are the grisly figures involved?
First, we have to assume that this comparison sets automotive fatalities against all uses of weaponry, including acts of war. If that is the case, weapons win hands down.
This is for a number of reasons, the first being that, unlike weapons, the automobile was not designed with efficiency of death in mind: most road deaths are accidental. Furthermore, while spears, guns and explosives have been available for centuries, automobiles have only been around for about 120 years. They have only been in mass production for 100 years and accessible to most of the world’s population for 60 years.
So what are the numbers? On the roads of the USA there has been an average of between 40,000 and 50,000 fatalities annually since 1970. If I were to extrapolate those numbers over 100 years (which would be to claim 50,000 died in years when there were barely 50,000 autos in the USA), then double the numbers again to try to include Europe, Russia, Japan and Australia, I would come up with slightly more than 10 million fatalities over the century.
In contrast, during the Second World War alone, combat deaths have been estimated at around 20 million. Civilian deaths by weaponry – including bombing and atomic bombs, but excluding the Holocaust, famine and other events – could probably total 20 million. I would argue that, unless millions of fatalities in remote lands have gone unreported, the allegation incriminating the car is unfair.
However, excluding warfare from the calculation would at least create a debate. Firearm deaths in the USA in 1999 totalled 28,874, of which more than 16,500 were suicides, 10,800 were murders and the rest were accidental or undetermined. According to the US National Safety Council, motor vehicle deaths in that year totalled 42,401.
Alexander D. Mitchell
Baltimore, Maryland, US
Although the statement concerning the relative lethality of motoring compared with warfare is a canard, like some myths it does have a kernel of truth. It originated during the 1980s in revisionist historical reassessments of the US involvement in the Vietnam War, when it was claimed that more young men were killed each year on American roads than died fighting in the jungles of south-east Asia.
In fact, during a decade of fighting, losses by the US armed forces totalled 47,378 – only slightly more than the average of 45,000 people killed each year in automobile accidents on American roads during the mid-sixties. Ironically, most of the 10,824 non-combat fatalities that US forces suffered in the conflict have been attributed to some kind of vehicular accident. Moreover, the highest casualty rate in both Vietnam and on the roads occurred in the same group: men in their late teens and early twenties. So from a revisionist perspective, going to war was almost 10 times as safe as driving a car.
Even if there were a basis for comparison, the Vietnam casualty factor was quite specific to the US armed forces. For example, the total death toll inflicted on the indigenous population – civilian, military or insurgent – during the Vietnam War was between 12 and 13 per cent which, had the US population suffered proportional casualties, would have left 28 million Americans dead.
Norwich, Norfolk, UK
The table fork is by far the deadliest weapon created by humans. Each year, this humble utensil abets the deaths of millions of people by conveying into their bodies all kinds of fatty foodstuffs known to cause heart attacks, cancers, strokes, diabetes and other diseases. According to the World Health Organization, approximately 17.5 million people died of cardiovascular disease alone in 2005, making up 30 per cent of all deaths globally.
As most of these harmful foods are of animal origin, and because the question doesn’t specify human lives claimed, we might also add the number of animals killed to be eaten with forks to the yearly death toll. This amounts to about 56 billion, says the Humane Society of the United States.
Physicians Committee for Responsible Medicine
Washington DC, US
According to several research studies, the US death rate due to medical misadventure is around 225,000 deaths per year, made up of 12,000 deaths due to unnecessary surgery, 7,000 from medication errors in hospitals, 20,000 caused by other errors in hospitals, 80,000 fatalities from infections in hospitals and 106,000 deaths due to the negative effects of drugs. So arguably the most lethal invention is in fact a doctor.
Perth, Western Australia
By not considering the less developed countries, some of your previous correspondents have neglected nearly 90 per cent of deaths caused by road traffic accidents. The World Health Organization estimates the total is 1.2 million deaths per year, the majority of these probably being pedestrians and cyclists.
It is also necessary to add the deaths from ‘traffic-related air pollution’, as another WHO report terms it. These have been estimated as between 0.8 times (in New Zealand) and three times (in Switzerland) as high as the accident-related death rate, so perhaps it would be correct to double the estimate of deaths due to motor vehicles to 2.4 million.
We should also factor in an estimate for deaths due to climate change caused by vehicle and petroleum industry carbon dioxide emissions. A definite value for this number of deaths will presumably remain unknown until it starts to reach tens of millions per year, because it is difficult to attribute individual droughts, storms or floods to climate change.
Even disregarding climate-change deaths, however, the current annual rate of deaths due to motor vehicles is at least double that caused by war.
By email, no address supplied
Sick as a horse
On a long motorway journey while driving behind a horsebox, I wondered, do horses get travel sick? In fact, do we know whether any animals besides humans suffer from motion sickness?
Newthorpe, Nottinghamshire, UK
Horses are unable to vomit, except in extreme circumstances, because of a tight muscle valve around the oesophagus. So it is difficult to know whether or not they feel sick. Other monogastric animals can vomit. Younger cats and dogs frequently vomit during their first car journeys but rapidly become accustomed to travel and no longer suffer sickness. In the UK a neurokinin-1 receptor antagonist has recently been licensed as a treatment for motion sickness in dogs as it reduces the urge to vomit.
Taunton, Somerset, UK
Motion sickness is common among animals, affecting domestic animals of all kinds. A carsick dog is not only pathetic, but messy. In his unforgettable book, A Sailor’s Life, Jan De Hartog wrote: ‘My worst memories of life at sea have to do with cattle. Two things no sailor will ever forget after such an experience are the pity and the smell… cattle get seasick, and the rolling of the ship terrifies the wits out of them. A seasick monkey or pup may be amusing and easy to deal with, but five hundred head of cattle in the throes of seasickness are a nightmare…’ He also mentioned horses explicitly and even fish transported in unsuitable conditions may show signs of disorientation.
Motion sickness is ubiquitous because all vertebrates have organs of balance and they correlate balance with feedback from other senses to stay upright. When movement causes, say, visual information to conflict with balance, the brain of a sensitive individual interprets the disorientation as a symptom of poisoning and a typical reaction is to vomit to clear the gut.
Somerset West, South Africa
Both Robert Falcon Scott and Ernest Shackleton took ponies with them to Antarctica. On the way they experienced some appalling weather, and both noted how badly affected their animals were. They did, however, perk up when the storms abated. Similarly, Scott’s dogs spent most of the storms curled up or howling, suggesting they too were suffering. Animals with a similar auditory system to ours would suffer from motion sickness, because it is caused by the confusion of auditory and visual inputs.
I heard that a Formula 1 car travelling at 200 kilometres per hour would generate enough downforce (or suction) to allow it to stick to the ceiling. Is this correct? And if it is, how is the force generated?
This is an interesting thought-experiment and gave us some great answers. Clearly the long-running debate over how aircraft wings achieve lift is still alive and kicking – Ed.
The short answer is ‘yes’, and downforce is the way to do it. Downforce acts towards the road, whatever the road’s orientation, and it increases roughly with the square of the vehicle’s speed. Driven fast enough, the downforce exceeds the weight of the car, which could then run along the ceiling of a tunnel. Depending on the set-up, the downforce and the weight of an F1 car typically become equal when the car is running at 130 kilometres per hour.
Filling a wardrobe with clothes boosts its weight. This increases the friction between it and the floor, making it harder to slide. An F1 car designer wants to increase the friction between the tyres of a car and the track so that it can carry more speed into corners without sliding off. But the designer wants to achieve this without increasing its weight.
So downforce is the answer and it can be achieved in two ways. First, upside-down wings are angled to deflect air upwards, away from the track, resulting in a reactive force on the car in the opposite direction. Second, designers exploit the Bernoulli effect. Pass air through a narrowing gap and it speeds up. This is what happens beneath an F1 car because the space between the ground and chassis represents a constriction to the airflow. According to Bernoulli’s principle, this leads to reduced pressure under the car. The ambient pressure above the car is higher than that beneath it, leading to a net force in the direction of the road.
Tunnels would need to be adapted to allow racing cars to run along the ceilings, which would make for some interesting overtaking manoeuvres on street circuits with underpasses like Monaco. It would also lead to spectacular crashes: any car that braked heavily while running along the ceiling would lose its downforce – or ‘upforce’ in that scenario – and fall, upside down, onto the track below.
Willenhall, West Midlands, UK
In theory, yes, an F1 car could drive upside down – but only in theory. Racing cars generate a substantial part of their downforce by creating a low-pressure area under the car. This was most apparent in the late 1970s, when the cars started using skirts that went all the way to the ground in order to contain the low-pressure area. The Brabham F1 team even built a ‘fan car’ that sucked the air from under the car – ostensibly to cool the engine – creating a low-pressure area underneath. It was banned after its first and only victory, in part because it was impossible to follow closely because it spat stones and other debris out of the back into the faces of oncoming drivers.
Three factors are key. Is the ceiling strong enough to withstand the force of the car pushing against it? Is it flat enough to allow the car to run close enough to the ground to generate the required downforce? And finally, you would have to get the car up there in the first place. No doubt if someone built a tunnel long enough, a car could drive up using a curved ramp built into the walls.
Then there’s the problem of grip. Because the car is being held up by airflow, this is the only thing pushing the tyres against the ceiling, so the driver would have very little control over the car. It would be difficult to generate braking without the wheels locking up and, if the driver tried to turn the car too quickly, it would skid. Then, if it were no longer facing forwards, it would lose its ‘upforce’ and fall. Because the car relies on the tyres for directional stability, and has no control surfaces like an aeroplane, the driver would be unable to ‘land’ the car back on the ceiling again.
Marco van Beek
F1 cars are capable of generating up to three times their weight in downforce. An F1 car has wings, but these are mounted upside down, generating negative lift which pushes it against the ground.
Ground effect is also used; the underside of an F1 car is completely flat and the closer it is to the ground (its ride height), the smaller the gap becomes. Air travelling under the car is forced to travel faster than air above it, generating further negative lift. Ride height is regulated in Formula 1 because if the car bottoms out or hits a bump the downforce and traction are lost. Such an incident was claimed to have been a contributing factor in the crash that caused the death of former F1 world champion Ayrton Senna in 1994.
Nevertheless, the aerodynamic design and relatively low weight of an F1 car would, in theory, allow it to race upside down.
Automotive engineering student
A single Formula 1 car passing by makes a noise of around 110 decibels. Last year I went to a Formula 1 Grand Prix and sat near the start line, where 20 cars left the grid at once. The noise was mind numbing, much louder than a single car, but not 20 times louder (or 2,200 decibels, an unachievable figure). Why wasn’t it?
There are two things here. First, the sound sources are not synchronised: the cars are making noise independently of one another, and so a burst of loud noise from one might coincide with a drop in noise from another. For these unsynchronised sound sources, the sound pressure (the air compressions that your ear detects) increases only according to the square root of the number of sources.
Second, the decibel (dB) scale is logarithmic: things don’t just add together neatly. The increase in the decibel level is the logarithm of the ratio of the number of sources (in this example, 20/1) multiplied by 10. The 19 extra cars add only around 13 dB, so the noise from 20 cars will be just 123 dB or thereabouts.
The same is true for violins in an orchestra. The 16 violins in an orchestra produce only four times as much volume as a single violin: if one violin produces 70 dB, 16 produce 82 dB. Similarly, silencing half of the trumpets – which are obviously much louder than violins – only reduces their volume by a few decibels, which explains why you need so many more violins than trumpets in an orchestra.
This also has implications for traffic-noise control. If the noise emanating from a car engine is roughly the same level as the noise from its tyres then there’s not much point in reducing engine noise by more than about 3 dB without also reducing the tyre noise.
University of Cambridge, UK
Back in 1990, I measured sound levels at a Formula 1 Grand Prix at Silverstone in the UK for health and safety. I found that the sound level from a single car passing, measured in the pits, was indeed about 110 dB.
The sound level varied widely throughout the race. In the first lap, all the cars passed by my measuring point virtually at once, but at the end all the cars were well spread out around the track. The difference in maximum level between the first lap and later laps where the cars were spread out was variable but around 12 dB, close to what theory predicts.
Loudness to a human observer is another matter altogether and differs from recorded sound levels. The human ear works using ratios, so doubling the sound power always produces roughly the same increase in loudness, no matter where you start.
A rule of thumb that works pretty well for most people is that an increase of 10 dB corresponds to ‘twice as loud’, so 20 cars passing at once would be a bit more than twice as loud as one car to a listener such as your questioner – the 13 dB given by the first correspondent.
This just goes to prove that the decibel is a very confusing unit of measurement. With this in mind I’ve taken on the challenge of explaining decibels for people who don’t know what a logarithm is, at bit.ly/decibels.
Point the way
When the Apollo and other similar space capsules were returning to Earth it was important for the larger end of their bell-shape to face downwards. This is because the protective shield that resisted the intense heat created on re-entry by atmospheric friction as the spacecraft slowed was positioned there. How were the capsules designed so that they would always keep the larger, protective face towards the Earth and not flip over so that the pointed end faced earthwards? It seems to me that this would be likely to happen as this orientation would minimise air resistance. Or is my grasp of space flight a bit flimsy?
It is a common misconception that spacecraft entering the atmosphere do so while going straight down, towards the Earth. This is perpetuated by just about every space movie ever made. The truth is that the spacecraft are going nearly horizontal as they enter the atmosphere, even when returning from the Moon. They remain within 5 degrees of horizontal until they have lost 75 per cent of their speed.
It is the location of the centre of mass that determines which end points into the wind. In this case, it is very close to the heat shield. The centre of mass of the Mercury space capsules was aligned with its central axis and these craft made a ballistic re-entry, meaning there was no lift.
With the Gemini and Apollo capsules, the centre of mass was offset from the central axis. This made the heat shield tilt slightly so that it was not perpendicular to the relative wind. This provided a small amount of lift, which made re-entry a little longer but reduced the peak acceleration from between 10 and 12g to around 3 or 4g.
Orlando, Florida, US
The orientation of an unguided body moving through a fluid depends approximately on the relative positions of the centre of mass and the centre of pressure. The centre of mass is the point about which the weight of the object would balance. The centre of pressure is the point about which aerodynamic pressures balance and, broadly speaking, the body will orient itself so that its centre of mass is ahead of its centre of pressure.
A classic example is an arrow. If you throw an arrow sideways, it will rotate until the head is foremost. This is because the heavy arrowhead places the centre of mass towards the front, while the fletching (or flight vanes) places the centre of pressure towards the rear.
The Apollo capsule was designed with the heavy equipment cradled in the deep, rounded bottom of the spacecraft, while the crew compartment – much of which is empty space – was towards the pointed top. This placed the centre of pressure behind the centre of mass, which stabilised the capsule as it fell through the atmosphere. The centre of buoyancy (which is related to the centre of pressure) was also above the centre of mass, thus keeping the capsule upright as it bobbed in the sea after landing.
You can encounter a dangerous example of this with a poorly designed model rocket. If the rocket’s fins are too small, or the mass of the engine and fuel too far to the rear, the centre of pressure will actually be ahead of the centre of mass. This will make the rocket highly unstable at launch, often spinning like a top as soon as it rises off its launch pad and tower.
However, as the fuel burns, the rear of the rocket will get lighter, moving the centre of mass steadily forward. If this moves the centre of mass ahead of the centre of pressure (where it should have been in the first place) the rocket will suddenly stabilise and start moving in a straight line, although in a random – and perhaps extremely hazardous – direction.
Melrose, Massachusetts, US
The right path
A pathway in my neighbourhood splits at an incline into both steps and a slope. Which option requires more calories to walk up or down?
The answer is complicated. Stair-climbing is more efficient than walking up a ramp, so it costs less energy. What’s more, ramps of the same steepness as an average flight of stairs are impossible to climb.
Very shallow slopes take a long distance (and walking time) to reach the same height as steep steps, so more energy is used overall. However, when climbing the steps, energy is used at a greater rate, which makes steps feel like harder work. In each case the gradient is important – steps with smaller risers and ramps with a shallower gradients feel less tiring because the rate or intensity of work is less.
Professor of Clinical Physiology
Derby City General Hospital