Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed upon it.

Jamie is the first to fly.

It's the summer he and his older brother spend at their grandmother's house -- Jamie is four and David eleven. The two boys have climbed up on the top of their grandfather's tool shed -- the large old elm tree makes a convenient ladder, and they stand on the sticky tarpaper roof.

It's been a warm day and evening is coming on. Fireflies are tiny sparks in the fading light, and Jamie is starting to wonder if being up here is such a good idea.

He's wearing one of his grandmother's good bath towels, the bright blue terrycloth secured over his small shoulders with a large safety pin. The towel comes all the way down past his feet and puddles behind him, and he can't help but think that Superboy would never have this problem.

For that's who he is, Superboy, and he's going to fly off this roof. His brother has promised.

Still, it's a long way down, and looking over the roof edge, he can feel his heart beginning to thump in his narrow chest. He tries to step back from the edge but David is right behind him.

"David, I don't wanna do this," Jamie says.

"Too bad," his brother answers, and pushes him off.

For just a moment, he is flying, and Jamie feels an exhilaration in his blood like he's never felt before.

Then he hits the ground. His right arm snaps in three places, and after that they don't go back to their grandmother's place for a few years.

Force is equal to the change in momentum (mV) per change in time. For a constant mass, force equals mass times acceleration. F equals m a.

Jim is drunk, and he's making love, lifting and plunging into his girlfriend like he's got wings sprouting from his back. The night is old and he's young, and he's so high on endorphins and French brandy that he feels as if he's above the earth, soaring over the nearby Saint Lawrence.

Her name is Lisette, and she's beautiful, the most beautiful girlfriend he's ever had, dark hair and gray eyes and did he mention that she's beautiful? She seems to think he's beautiful too, which is just extraordinary -- no one has ever told him this before, and it makes his heart rise in his chest like a hawk climbing a ladder of sky.

He's less than a year away from graduation, and he can finally see the end of his university lessons and the beginning of his practical education as a physician, but in the meantime, in the here and now, there's this.

He plunges again; he's resting his weight on his forearms and whispering in her ear. He's telling her he loves her and he already knows he doesn't mean it and might not even remember it in the morning, but right now she's got her legs and arms wrapped around him and she's whispering too -- sibilant Quebecois syllables that brush like feathers around his ears.

When he comes he gasps, and she gasps, and then he's falling on top of her like an angel struck from the heavens. His wings fold behind his back until the next time.

If there is a next time, another night as perfect as this.

For every action, there is an equal and opposite re-action.

Wilson stares at the Clinic patient (Mr. Blalock, his brain helpfully supplies), who is staring back at him in alarm. Wilson is absolutely sure he can tell what Mr. Blalock is thinking -- This is a hospital clinic -- the doctors aren't the ones who are supposed to be sick!

"Dr. Wilson?" Mr. (Artie, his brain chimes in, and why won't it shut up with these non-essential details) Blalock asks. "Are you okay?" And Wilson wants to tell him no, he's not fucking okay, he's having a heart attack, an infarction, a coronary event that might just kill him -- he wants to say all this but can't. There's a cold sweat on his brow and an elephant on his chest, and the pain is crushing him to his knees.

As Wilson settles quietly into a sitting position, his shoulders braced against the exam room wall, Mr. Blalock does at last what Wilson had wished he would do five minutes ago -- he springs to his feet and bolts out the door, shouting "Hey! Is there a doctor around here?"

Wilson is flying down the hospital corridor. He's flat on his back, so the hallway lights are flashing by like strobes, adding to the surreality of his situation.

How can this be happening? he's thinking. I'm only thirty-eight!

Remember Uncle Izzy? his brain admonishes. Izzy Engelmann? Dropped dead at thirty-five. It runs in the family. Wilson suddenly realizes his brain sounds a whole lot like his mother. He wonders what that says about his life. It means you should've listened to me more often, his brain says reprovingly, and Wilson can only agree.

The lights are slowing down, which means they're almost to the ER. The forward motion stops, and strangers' hands are all over him, cutting off his clothes, blunt scissors slicing apart his white dress shirt like a butcher dismembering a swan. His chest is laid bare, and the cool dry air of the Emergency Room is a soothing shock.

The voices of the strangers in the ER are blending together into an indistinct hum, except for one, and Wilson would recognize that voice anywhere. Somehow House has found him, and he's yelling in Wilson's ear.

"Wilson!" House shouts. "Come on, I need for you to stay with us!" A familiar hand slips into his. "I've got you! Stay with me!" Unfortunately, as much as Wilson would like to oblige (and when has he ever denied House anything?) his heart chooses that exact moment to stop beating.

Very faintly, Wilson can hear someone saying "Clear!" in a loud, determined voice, and he knows his body is jolting on the table, straining upwards as the small birds of the field do at the sound of the hunter's gun.

And then ... he's on the roof of his grandfather's tool shed, only instead of a bath towel pinned against his neck, he's wearing his lab coat draped over his shoulders.

"Come on, Wilson," someone shouts, and he takes a tentative step forward, looking over the edge.

House is standing down there, without his cane, and Wilson knows he's in uncharted territory. Don't you think the fact that you're standing on Grandpa Jake's toolshed should've been your first clue? his brain asks sarcastically, but now his brain sounds like House and he ignores it.

"Wilson!" House shouts again. He's holding his arms out, palms up.

There's a hot breath in Wilson's right ear. "Can't stay up here forever," his brother says.

Wilson looks down again. House is still there, arms spread wide. "Come on," he yells. "I've got you!"

There's a buzzing in Wilson's brain, faraway stations fading in and out.

House is waiting.

Wilson throws out his own arms, launching himself as far up and out as he possibly can. His lab coat spreads behind him like a cape.

He can only trust that House will catch him.