There's a world of difference between the two. You're using the same voice: maybe that of your narrator, your character – or your own voice, the voice of the writer.
But the words will vary. With action, you'll want to mimic fast movement. So your words will be short. And so will your sentences. In some cases, you'll wish to allot a paragraph to each sentence – even if it's only a single word.
Your aim is to focus the reader's attention on each and every action.
The last thing you want to do is to bore your reader!
Action can be anything from a battle between rival fleets of starships to somebody losing a contact lens in a washbasin. What both have in common is that they must be short, sharp and to the point.
The following occurs in an early chapter of my new novel, The Faustian Gambit. Portia, the heroine, is on the Cooley Peninsula, together with Myles, her fiancé. They're heading for a house owned by his uncle. It's big: about 20 times bigger than Anaverna!
It's night. They've just driven through a snow storm. A mysterious woman ran across their path, causing Myles to swerve the car. It skidded and ended up in a snowdrift. They're shaken but unhurt.
The novel is written in the first person singular: Portia's point of view.
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"You're upset."
He took my hands in his. They were trembling.
"It was nothing."
But I was already opening my door.
"What are you doing?"
"Going to take a look."
"Portia!"
"If you want to help then get the torch. It's in the glove compartment."
He caught up with me before I'd gone more than two or three metres, my boots breaking the crust of the crisp snow like a fork in meringue.
My knees were cold; I regretted not having put on thicker tights and a warmer skirt.
Myles played the torch's beam from left to right, right to left.
Nothing.
The trees were a black wall against which nothing moved.
The moon came out then, very briefly, but showed no more than the hand-held light had done.
The flashlight's beam moved erratically. It lanced into the treetops – and went out.
I turned quickly.
"Myles!"
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That's all you need for an action sequence: the action. And short, sharp dialogue. Of course you'll need to include some description, but it must be pared to a minimum. As long as you've set the scene earlier, your reader will know where your characters are, the setting they find themselves in.
setting the tone
A descriptive passage, on the other hand, should move at a very leisurely pace. If action is an athlete doing the 100-metre dash then description is your granddad out for a Sunday stroll.
Your emphasis here will be on atmosphere. Think of it as the opening sequence to a scary movie, when the camera is looking slowly about a room, pausing in dark corners, zooming in on a spooky portrait on the wall – that sort of thing.
Your sentence structure will reflect this. Your words can be interesting (without being purple). Your sentences will be a lot longer than those describing action. You want to slow your reader down.
The sequence below is taken from the same chapter of The Faustian Gambit. Myles and Portia have resumed their journey to Whitethorn Hall, home of Myles's uncle.
They've recovered from the incident in the woods. Peace has returned. Now Portia has more time to look about her, to study her surroundings.
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Breaking out into the moonlight again, we caught our first sight of the house.
It was massive, bigger than I'd expected. I didn't know much about such things but thought it foreign: English or French perhaps, for it seemed not to belong here. It was built entirely of brick. I could only guess at the colour but it was pale. I wondered how it would look in full sunlight.
The moon seemed brighter now, almost a silver simulation of the sun. Dimly I recalled something written by the poet Robert Graves; it concerned a neolithic site in Britain – Stonehenge I believe – a place where the sun and moon seemed closer to the earth than any other vantage point on the planet. I didn't understand it at the time, thought he was being, well, poetic. But some years later it occurred to me: he must have been referring to the winter solstice; oddly enough, it's in and around this time of year when we get perihelion in the Northern Hemisphere – and that's just the time when the sun is indeed closest to the earth. He might as well, I concluded, have been writing about Whitethorn Hall.
But I digress. The house was having a wondrous effect on me – and I could tell Myles felt it too. I'll try to describe it as best I can. It was perfectly symmetrical, in the way such big country houses are. There was a grouping of square towers on either flank; all were castellated and they sloped off progressively. Directly behind the entrance rose an even higher tower. In the moonlight my impression was that of a hulking bird of prey, an eagle perhaps, crouched with partly furled wings.
There was an entrance porch, complete with an arch and a raised coat of arms. The windows – and there were many of them – were trellised and strangely eyelike. I was put in mind of an ancient church, or even a monastery. I glimpsed what appeared to be a small dome atop one of the highest towers, to the right of the entrance, before it fell away out of sight as we neared the building.
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You'll have noticed that we're inside Portia's head. The excitement has died down, and she has time to think. She remembers stuff, compares what she sees with old experiences. She's a poet as well, hence her poetic language.
So that's War and Peace contained within a single chapter :0)