In many of the episodes, Scotty tells Captain Kirk something along the lines of, “I can’t give you warp 9 much longer, captain! The core is overloading!!!”
So here’s the question: once the Enterprise reaches warp 9 or whatever, why do the engines need to be kept on? Why can’t they just be turned off?
As a wild assed guess I’d say that the power goes to creating and maintaining the warp field around the ship and not in maintaining propulsion as we understand it. Thus if the power is stopped, instead of continuing on via inertia the warp field would collapse and cause the Enterprise to fall into normal space thus slowing down drastically.
The in-universe explanation is that warp travel is accomplished by generating a “warp field.” It does not operate according to Newton’s laws, and inertia is not really in operation*.
The real-world explanation is that the Enterprise, like most sci-fi starships, is analogous to a battleship at sea, and the audience needs the cause-and-effect of “engines working makes ship go, engines working harder makes ship go faster.”
Warp speed warps space (that’s why the nacelles are separate and behind the rest of the ship). You need to apply energy to keep up the speed or else you drop out of warp with no power.
Real-world explanation:
It makes it all more dramatic.
I’ll bet warp drive is different than just shooting through space like a meteor. it seems to involve “warping” the fabric of “space- time” in a way that allows faster-than- light travel. it must require constant power.
According to “The Naked Time,” if you turn off the engines (like Riley did), it “de-activates (?)” the anti-matter, and you have to begin a long warm-up sequence (or the engines will implode and you’ll travel backward in time and have to clutch your blonde yeoman).
This happened more than once, e.g., when they were chasing the Gorns in “Arena” and (in particular) when they were chasing the giant amoeba in “Obsession.” In addition to the explanations offered above, note that the maximum safe cruising speed of the Enterprise was always Warp 6, though it could be pushed to Warp 8 in extreme emergencies. Anything higher than that was considered dangerous, since the ship’s field mechanisms weren’t able to compensate for it.
I always found it interesting that despite all the technical advances made in the intervening 78 years, the ships in Picard’s day couldn’t manage to go any faster than this either. It took “trans-warp” technology to get past that hurdle, and only the Borg seemed to have mastered that!
Yes; you can’t mix matter and anti-matter cold. You need thirty minutes, and you can’t change the laws of physics, either! 
FWIW, this was explained in the TNG Technical Manual: the speed of ships increased greatly over time, so much so that warp factors were redefined over the years. Warp 8 in the Enterprise D was considerably faster than warp 8 in the original.
Well, then, why not have it just go to ten and have ten be the highest number? :dubious:
10 is the highest number. The number that can’t be reached because it’s infinite speed and infinite energy.
And they quite regularly move at Warp Factors in excess of 9.
“These go to eleven.”
Pardon the hijack, but here’s something that’s continuously bothered me:
In Star Trek IV: The Voyage Home, the Enterprise crew slingshots around the sun fast enough to send themselves back in time. However, towards the end of the movie, the exact same procedure sends them forward in time. How on earth does that work?!?
In the TOS era, Enterprise and other vessels moved at warp factors in excess of 10 pretty often, even if under extraordinary circumstances.
It’s been hand-waved/fan-wanked/retconned. The primary “canon” handwave is that between TOS and TNG “they” “redefined” Warp 10 as “infinity and beyond” or something like that.
The second time they slingshot backwards around the Sun.
Reality: It works according to Needs of Plot.
Counterclockwise = backwards. Duh.
Nonsense. They reversed the polarity.
I bet that reversing the polarity would do that.
(ninja’d)
But they really aren’t simply slingshotting. When you generate a high-level warp field in a deep gravity well, you can end up almost anywhere on a closed time-like loop.
IIRC (which is by no means certain), the TOS Technical Manual stated that the warp factor squared equals the multiplier of lightspeed, i.e., warp 1 is lightspeed, warp 2 is 4 times lightspeed (2 squared), warp 3 is 9 times lightspeed, etc.; and the TNG Manual said that in the Enterprise D’s time, the warp factor is cubed instead of squared.
I see.