[MCllorf]

I've always been curious on this question because I don't have any physics background.

If you made something like a gravitron ride on the moon, would it take a slower rotation speed to reach perceived 1g than if you spun up a ring station in orbit? This calculator makes it seem like you could get pretty close to 1g with just a bullet train running on a 3.14 kilometer loop.

It seems like the main thing stopping earth trains from being faster is that most of our tracks were built a really long time ago and it's not worth the effort replacing them, but if metal is readily available and you're laying new track already, designing for ~300km/hr wouldn't be that much of a stretch no?

[kragen]

Yes, a little. In freefall, such as on orbit, you need 1 gravity of centripetal acceleration. a = v²/r; v = √(ar); if we assume a 3-meter radius (roughly Gravitron size) we need about 5.42 m/s tangential velocity to get one gee. The moon's gravitational acceleration is 1.62 m/s/s; to find the centripetal acceleration needed to get a Pythagorean sum of one gee, we take √((9.81 m/s/s)² - (1.62 m/s/s)²) = 9.67 m/s/s. That means that now our √(ar) tangential velocity is just 5.38 m/s, which is less than 5.42 m/s. Does that help?

The main thing stopping earth trains from being faster is politics, not engineering. Trains have been occasionally going over 300 km/h since 01955, decades before maglev. The Shanghai Maglev Train has been running at 430 km/hr since 02004. The Euroduplex regularly runs 320 km/hr on regular 1435mm standard-gauge rails and reached almost 575 km/hr in a test in 02007. 300 km/hr trains have been in regular service since 01989. There are several other train lines that run over 300 km/hr, in Taiwan, PRC, France, Belgium, Saudi Arabia, Japan, Germany, the UK, the Netherlands, Italy, Spain, Korea, and Switzerland. Soon India and the US will join them.

The big advantage of maglev is actually not smoothness or absolute speed but acceleration and deceleration.

https://en.wikipedia.org/wiki/Euroduplex https://en.wikipedia.org/wiki/High-speed_rail#Speed https://en.wikipedia.org/wiki/List_of_high-speed_trains https://en.wikipedia.org/wiki/Maglev#Comparison_with_convent... https://en.wikipedia.org/wiki/Taiwan_High_Speed_Rail https://en.wikipedia.org/wiki/Bombardier_Zefiro https://en.wikipedia.org/wiki/Centripetal_force https://en.wikipedia.org/wiki/Euclidean_vector#Addition_and_...