# 2001: A Space Odyssey book physics

There's a passage in 2001 that struck me as wrong. They're describing the spinning of the carrousel in Discovery and there's the following quote.

The problem of shaving was also solved; there would be no weightless bristles drifting around to endanger electrical equipment and produce a health hazard.

However, a centrifuge doesn't create gravity, it just affects items that are touching it or recently touched it. So wouldn't the bristles still be free floating? They have the relative velocity of the shaver, but not towards the ground like it would be in gravity, they would travel in a diagonal to the floor, right?

• Another question: Why bother shaving while you are on a very lengthy voyage to Jupiter with a bunch of other men? Who the hell cares if you have a beard? Commented Jun 24, 2015 at 20:08
• Because for some of us facial hair can be very, very itchy if it gets too long. Commented Jun 24, 2015 at 20:40

No. The objects inside the spinning wheel will experience an artificial gravity effect which appears to be pushing outwards from the center of the wheel. Since all the objects inside the station (including your bristles) already have a considerable amount of motion relative to a stationary observer outside, they will simply travel to the outside wall (e.g. the floor).

A pretty solid explanation can be found here on the Cornell University website or on our very own Physics:SE stack; Artificial gravity on rotating spaceship?

Quoting shamelessly;

If you jumped "straight up", you would still have a horizontal component of velocity (relative to a nonrotating frame), so you would still end up coming "back down".

Likewise, the shower water is moving horizontally in a nonrotating frame, which makes it collide with the floor eventually (since the floor is curving upwards in the nonrotating frame). But to a person on the ship, it looks as if the water was moving downwards, rather than the floor (and you) moving upwards.

• Perfect answer. :-) Commented Jun 24, 2015 at 19:23
• Great answer. I would add that most of the molecules of water in a bucket don't touch the bucket itself, but when you whirl the bucket in circles by the handle, those molecules still stay inside. Commented Jun 24, 2015 at 20:05
• Richard - why isn't this an off-topic question? Isn't it asking for real world explanations of a fictional story? I have been wanting to ask if the earth would be able to exist normally if Jupiter turned into a star, as happened in the sequel to 2001, but I haven't because I was sure it would immediately be closed as off-topic. Am I wrong about that? Commented Jun 24, 2015 at 20:12
• @WadCheber - meta.scifi.stackexchange.com/questions/350/… Commented Jun 24, 2015 at 20:15
• @WadCheber - For the record, your Jupiter question would be off-topic (generally), however it would be on-topic if you asked if there was an in-universe explanation. Commented Jun 24, 2015 at 20:16