# Why does the Endurance rotate in Interstellar?

In the 2014 film Interstellar, why does the spacecraft Endurance spin? I think it really has to do something with physics?

### It rotates to create artificial gravity

A rotating space station is a known concept (apparently Tsiolkovsky thought about it in the very beginning of 20th century). It uses the rotation to induce a centripetal (acting towards the centre) acceleration on the people inside.

In order for a body to stay in motion with constant speed in a circular path with radius R, it must have an acceleration equal to the square of its linear speed divided by the radius R (or the square of its angular speed multiplied by the radius).

This acceleration is actually caused by the normal force exerted by the floor of the station on the people - the people inside would be hurled into space, but the floor keeps them in the circular path, so they feel an acceleration which is similar to the acceleration due to gravity.

From the Wired article

As to why it's needed at all - remember that Endurance is not a fast flier. It's supposed to be in space for a long time (Romilly spent 23 years there), and being subjected to weightlessness for a long time bone decay occurs. The simplest solution is to take gravity with you, and this is a plausible way to do that (though we are yet to see any such stations in real life).

• was just about to comment on your definition of centripetal... then you changed it entirely ;) Most people think it's centrifugal force... but it's not, it's centripetal. Aug 11, 2017 at 18:31
• I could say there's a centrifugal force (equal to inertia) which is trying to hurl people into space, but I find this one more intuitive. Aug 11, 2017 at 18:32
• Relevant XKCD: xkcd.com/123
– Mark
Aug 11, 2017 at 23:17
• You said yourself that "centripetal" means "towards the centre". If the dominant force acted towards the centre, they'd… move towards the centre. You do mean "centrifugal", which means "fleeing the centre". In any normal conversation, the terms mean exactly what they say. Gravity is similarly a fictional force, but no-one says it doesn't exist. Aug 12, 2017 at 8:22
• @Gallifreyan Well, as long as you also never refer to Coriolis force or to the force that presses you back when you accelerate, I suppose it's consistent. But words are there to get people to understand you. A minor technical detail like "a tomato is not a vegetable" or "centrifugal force doesn't exist" just hinders conversation in many cases. Why would you not take the reference frame of the spaceship, anyway? It's the only interesting thing in that region of space. Aug 12, 2017 at 9:41