The metal container powered by the explosion of million-year-old liquefied algae which transports me over long distances (My car. Yes, I know I’m a smart-ass.) is a 2007 Toyota Yaris hatchback. It’s a decent enough car, I suppose. It looks about like this:
(Many thanks to the nice person on the Wikimedia Commons who put the photo in the public domain, since I lost the only good photo of my car before it got all scruffy.) According to its specifications, its engine can produce 106 horsepower (79 kilowatts), it weighs 2,326 pounds (meaning it masses 1,055 kilograms), and has a drag coefficient of 0.29 and a projected area of 1.96 square meters (I love the Internet). Those are all the numbers I need to calculate my car’s maximum theoretical speed. I’ll be doing this by equating the drag power on the car (from the formula (1/2) * (density air) * (velocity)^3 * (projected area) * (drag coefficient)) with the engine’s power. I will be slightly naughty by neglecting rolling resistance, which for my car, is usually negligible.
1. Maximum speed on Earth, at sea level: 135 MPH (217 km/h or 60.19 m/s). I may or may not have gotten it up to 105 MPH once, so this estimate seems about right. Worryingly, according to the spec sheet for my tires, they’re only rated up to 112 MPH…
2. Maximum speed on Mars: (Assuming I carry my own oxygen, both for me and for the engine.) 538 MPH (866 km/h, 240.50 m/s). I would break the speed record for a wheel-driven land vehicle (Donald Campbell in the BlueBird CN7) by over 100 MPH. And probably die in a rapid and spectacular fashion. But that’d be all right: I always wanted to be buried on Mars.
3. Maximum speed on Venus: (Assuming I avoid dying in burning, screaming, supercritical-carbon-dioxide-and-sulfuric-acid agony.) 36 MPH (58 km/h, 16.23 m/s). Unfortunately, the short-sighted manufacturers didn’t say whether my tires are resistant to quasi-liquid CO2 at 90 atmospheres. The bastards.
4. Maximum speed underwater: This is the one we’re all here for! Water is dense shit and puts up a lot of resistance, as anyone who ever tried running in a swimming pool can attest. Maximum speed: 15 MPH (23 km/h, 6.52 m/s). Wolfram Alpha tells me I’d only be driving half as fast as Usain Bolt can run. I shall withhold judgment until we clock Mr. Bolt’s hundred-meter seafloor sprint.
5. Maximum speed in an ocean of liquid mercury: (Assuming we filled my car with gold bricks to keep it from floating to the surface. Also, why is there an ocean of liquid mercury? That’s horrible.) Maximum speed: 6 MPH (10 km/h, 2.74 m/s). I can bicycle faster than that (although not in a sea of mercury, admittedly). Of course, mercury is so heavy that, even if our sea was only 5 meters deep, the pressure at the seafloor would be high enough to make my tires implode. Which would, of course, be the least of my problems.
6. And finally, just for fun, my maximum speed in neutronium. Neutronium is what you get when a star collapses and the pressures rise so high that all its atoms’ nuclei get shoved together into one gigantic pile of protons and neutrons. It’s just about the densest stuff you can get without forming a black hole, and my car could push me through it at a whole 0.1 microns per second, which is only fifty times slower than the swimming speed of an average bacterium.
I’ve now spent far too long imagining myself being crushed by horrible pressures. I need to go lie down and imagine myself being vaporized, to balance it out.