The subject here is velocity: the speed and direction that a reader experiences when reading a sentence, a passage, or a paragraph. Everyone knows that some pages seems to move faster that others. It should be no surprise that we are grateful when we don't feel we have to fight our way through a text.
In general, a sentence should move along easily. Think of this quality as its velocity, and read over your sentence with an eye, and more importantly, an ear for velocity. How quickly and comfortably does your sentence lay out its meaning? Does it go on to long? Does it grind its gears? Do you feel your mind bogging down – even slightly – as the words go by? Are there specific words or phrases that hamper the easy ride from thought to thought? Does it step on its own toes with thoughtless repetitions, unplanned contradictions, or sloppy overlapping idea? Those are sure to drag on velocity. (I’ll explain later.)
Velocity is a tough one particularly for students. They are faced with the problem of having to produce X amount of words or pages in X amount of time, and naturally the sooner they can fill those pages the sooner they can use the leftover part of the X amount of time to do other things. So it’s natural for a student to welcome any possible excess verbiage to his or her pages. But just like giving a cross country runner a couple of suitcases full of bricks, excess verbiage is going to slow down the sentence. And a slow overloaded sentence is no fun to read. And it certainly won’t invite your reader to try another one. And yet . . . .
There are times when a fine writer may want to purposely lubricate the gears of his syntax with a more viscous oil. “Four score and seven years ago,” says the president at Gettysburg to get things rolling. Why not “Eighty seven”? Seems clear he wanted to call down the shadow of history as a backdrop for his first point. Notice how the sentence first rumbles with gravity (“Four score . . . .”), wanders into circumlocution (“brought forth upon this continent”) hovers for platitude (“conceived in liberty”), dallies on legalism (“dedicated to the proposition”), how it gathers, gathers to sharpen, like a doughy hand morphing into a gleaming blade, for its unadorned point: “all men are created equal” – not a word wasted.
But probably best not to try this at home! In general, you should keep it simple. You’re just writing a three-page paper, not burying the Union dead. And you only have a captive audience of one: your teacher. Make the ride easy, clear, and interesting, and your reward will be lavish.