Other mistake: After they take off from California, Kirk gives a heading to Alaska. He then tells Sulu "full impulse power", and Sulu says "aye, ETA 12 minutes." Full impulse is 1/4 the speed of light. No way they would use speeds like that to go a few thousand miles.
Star Trek IV: The Voyage Home (1986)
Plot summary
Directed by: Leonard Nimoy
Starring: William Shatner, George Takei, Leonard Nimoy, Walter Koenig, DeForest Kelley, James Doohan, Nichelle Nichols, Catherine Hicks
Admiral James Kirk of the Starship Enterprise is on the planet Vulcan, commanding his recently seized Klingon Bird of Prey and picking up Spock so they can go back to Earth to face charges for their crimes. However, life on Earth is not the best. A powerful alien probe has appeared out of nowhere and nobody knows what language it is speaking in . . . or more importantly, whom they wish to commune with. When they set Standard Orbit around Earth the oceans are being steadily vaporized; Spock figures out that the probe is calling to humpback whales. Problem is they have been extinct for the past two centuries!!!! Kirk and his crew 'Time Warp' from the 23rd to the "primitive and paranoid" 20th century. Along the way, they run into a marine biologist who is a bit protective of her two whales, George and Gracie. Also, the crew run into some 'technical' problems.
More mistakes in Star Trek IV: The Voyage Home
Kirk: Mr. Spock, have you accounted for the variable mass of whales and water in your time re-entry program?
Spock: Mr. Scott cannot give me exact figures, Admiral, so... I will make a guess.
Kirk: A guess? You, Spock? That's extraordinary.
Spock: [to Dr. McCoy] I don't think he understands.
McCoy: No, Spock. He means that he feels safer about your guesses than most other people's facts.
Spock: Then you're saying... It is a compliment?
McCoy: It is.
Spock: Ah. Then, I will try to make the best guess I can.
McCoy: Please do.
More trivia for Star Trek IV: The Voyage Home
Question: What exactly was Scotty's reason as to why giving the Company boss the formula for the one inch glass wouldn't alter the future? He gave a brief response, but I honestly can't think of any reason why it wouldn't do any future damage.
Chosen answer: Scotty says "Why? How do you know he didn't invent the thing!" If the man was in fact the inventor, this would only cause a slight causality loop problem - he "invents" it because they gave it to him, but they only know it because he "invented" it. However, since Sulu said earlier in the movie that it was about 150 years too early for transparent aluminum, it would seem they do know this, so it wasn't a smart thing to do. Of course, the real flaw in the plot is that they need the tank to be transparent at all.
Answer: The crew is resigned to the fact that their mission forces them to alter history in some fashion or another. McCoy just wants to acknowledge the gravity of their actions before they go ahead and do it, and Scotty's response is a cheeky way of reassuring him, "Hey, maybe it won't be that bad."
Answer: They only give him a schematic of the molecule. The man even says, "It would take years to decipher the matrix", or something like that.