Page 11

76

ATOM S U N DE R T H E F L O OR BOA R D S

them along. What’s much less obvious is that cars need air to breathe, just like people. The combustion that burns fuel in the cylinders is a chemical reaction between the hydrocarbons (molecules built from carbon and hydrogen) in petrol and oxygen in the air, so even if you’ve got a full tank of petrol, if there’s no air around you’re going nowhere fast. How much air does a car need, exactly? A sports car pants its way through something like 6,000 litres of air (6 cubic metres/1,300 gallons) per minute, which is about 250 times more air than a cyclist uses49. So if you drove your car continuously for about eight hours, it would breathe enough air to fill an Olympic-sized swimming pool. You might think air is just an airy-fairy consideration because, wherever you go on Earth, there’s always plenty to spare. In theory, the only engines that ever run short of air are the ones attached to space rockets. Since they blast out of Earth’s vast atmosphere, into the deep darkness where there’s no oxygen, they have to carry their own ‘air supplies’ (oxidisers) in giant tanks, as well as their own fuel. Is there anywhere on Earth where a car could run out of air before it ran out of petrol? It’s not very likely, but high altitude – and ‘thin’ air (low oxygen) – certainly makes a difference to how well a car runs. That’s simple science for you: if there’s a chemical reaction between A (fuel) and B (oxygen) to produce C (energy), and there’s less B, you’re going to get less C too unless you compensate somehow. Indeed, quite a few manufacturers have offered modified versions of their cars for mountain-top driving50. Generally, our bodies don’t much care for high altitudes either. If you’re pounding through the clouds in a mountaintop marathon, there’s less oxygen nipping down your nose to power your legs: respiration needs that all-important gas just as much as the cylinders in your car do. Long-distance runners have a positive disadvantage at high altitudes because they breathe in so much oxygen during a race.

Atoms under the Floorboard.indb 76

1/27/2015 8:39:50 PM

Atoms Under the Floorboards by Chris Woodford  

Seriously surprising science from the sofa!

Atoms Under the Floorboards by Chris Woodford  

Seriously surprising science from the sofa!