In a collision or explosion,
the total momentum before
will equal the total momentum after
in the absense of external forces.

...

Under the tangling mass of thick blonde hair and the amalgamation of papers and books sprawled across the desk, Courfeyrac can just about see the scrunched up pale face of his friend Enjolras amidst the mess. It seems awfully cruel to disrupt the man whilst he's so deep in thought with his brow furrowed and his tongue sticking out with concentration, but it's edging into his fifth hour and he's let this go on too far. He takes a tepid couple of steps forward and stands there, waiting for the other man to acknowledge his presence.

"I know you're there Courfeyrac," he sighs, not looking up from his papers. "I'm just choosing to ignore you. And before you say it, I'm not stopping working. And I'm not coming tonight."

"But it's Bahorel's birthday and there's going to be cake and everything-" Courfeyrac protests.

"All the more reason not to want to come."

"You really are a party pooper, you know that?"

"Good. Now will you please leave me alone to study?"

The upcoming university exam may be his excuse, but it's not his only reason for skipping out on the night out. Normally these sorts of outings would be held at the Musain- the bar in the student union- but seeing as the entire building has been shut down for renovations, they've had to relocate to a reclusive bar elsewhere. Enjolras just knows that his friends are going to use this all as an excuse to drink themselves into oblivion although the actual purpose is a meeting for the student society that he runs.

"Come on Enjolras! You don't have to come tonight, but you have to at least take a break from all of this," Combeferre appears behind Courfeyrac.

"No he has to come; he never lets his hair down. Just one night, for me?"

"C-can you just-..." Enjolras sighs and places his head in his hand, letting his pen fall onto the desk with a mighty thud.

"Courfeyrac, could you fetch a glass of water?" Combeferre pulls over a chair and sits beside Enjolras. "You are insufferable, my friend. You know working for too long will leave you with a headache."

"I'm okay-"

"How bad is the headache?"

"Feels like the beginning of a migraine," he hesitates before finally admitting what is wrong as Courfeyrac hands him the glass of water. "Thank you."

"Sorry. I just miss you when you aren't with us, that's all," Courfeyrac places a hand on his friend's shoulder. "I won't pester you about tonight, okay?"

"Just hold back on the studying," Combeferre adds. "I know it seems out of character for you, but please rest. You'll feel better if you do."

He sighs, accepting the defeat and trudges towards the sofa. He falls asleep almost instantly, and Combeferre quickly fetches a blanket to keep him warm. Jean Prouvaire arrives as Bahorel and Joly will be picking the trio up in about two hours' time. He smiles towards the bespectacled man as he steps in the door, but his smile quickly fades when he sees Courfeyrac standing in the hall.

He doesn't hate Courfeyrac; in fact, it's the absolute opposite. Things between them have been complicated for a while; they dated, broke up, argued and now are in the awkward stage where they're friends, but can't shake the history between them. Courfeyrac smiles awkwardly, a strange feeling of guilt building in his stomach as he watches the man enter the living room. He knows that he had been the one at fault, yet the 'sorry' lingers in his throat as a bitter memory washes over him, and the word never drifts past his lips.

...

"Are you sure you don't want to come tonight?" Bossuet asks Musichetta as she drops Joly and himself at the football cages.

"I have three lab write-ups to finish, I need the quiet night in," she laughs. "Without you two, I'll probably manage to get them finished for once."

The pair join Bahorel, Feuilly and Grantaire and kick a ball around. They'll be going to pick up the others in a couple of hours, but for now they have time to just relax and play a bit of football. They're about an hour into the match(Feuilly, Grantaire and Joly versus Bahorel and Bossuet) before it's clear which team is going to win.

"There's only one Paul Bahorel!" he celebrates a goal, shoving his hands in the air before tackling the ball off Grantaire again. "He dribbles the ball past the defenders, narrowly escaping Feuilly. He gets past Joly and he shoots... AND HE SCORES!"

"The only reason you're winning is because Courfeyrac isn't here," Feuilly laughs, grabbing the ball off of the ground and holding it under his arm. "So calm your ham and get a move on; we should go pick up the others."

"You are a stick in the mud, Feuilly. Can't we just play for another half hour?"

"What do you think it is, your birthday?"

"Yeah it is actually."

"Piss off."

"Oi, Oi! Be nice to the birthday boy!"

Grantaire hops into his own car with Bossuet and Feuilly and heads towards Cosette and Marius' house, whilst Bahorel and Joly take a little bit longer, but eventually end up at Combeferre, Courfeyrac and Enjolras' student flat.

...

"Is Enjolras not coming?" Joly raises an eyebrow when only three men appear at the door.

"Gave himself a migraine studying all day," Courfeyrac explains. "Don't look so worried, Jol'. He's fine."

"Can we go now?" Bahorel crosses his arms, smirking towards his friends. "The night is still young; I'd like to embrace it before it goes all old and wrinkly."

"Have fun!" they can hear Enjolras shouting as enthusiastically as he can muster in his current state(which is almost catatonic, his head moulding into the cushion of the sofa).

Piling into the car, it's a squeeze for three of them to fit into the backseat. Little Courfeyrac- the shortest of the group- is of course in the middle, with Joly and Jehan on either side of him. Combeferre- one of the tallest of the group- sits in the front seat, with Bahorel driving. If there's anything that Combeferre is afraid of(which is saying something, seeing as he doesn't get scared easily), it's this particular friend's handling of a car. He drives far too fast, passes through red lights almost daily, doesn't understand the meaning of a 'give way' sign and every turn sends his passenger's stomach's into their throats. Another swerve makes the car feel as if it's driving on only two wheels, and Joly almost gags with motion sickness as the car finally settles and Bahorel drives a little less recklessly.

"How did you even pass your driver's test Bahorel?" Courfeyrac fakes a retch.

"Believe it or not I can drive properly; driving recklessly is just a lot more fun," Bahorel grins.

"You're an asshole," Jean Prouvaire laughs whole-heartedly.

"That's a nice thing to say to the birthday boy..."

"What, so because it's the anniversary of your birth we have to be nice to you?" Joly smirks, shaking his head as a guffawing laughter rises in his throat.

"Yes you do actually. Or the birthday fairy will send you straight to hell."

"There's a birthday fairy now?" Combeferre sighs, chuckling under his breath.

"No I meant um... a birthday gorilla?" he tries to come up with something he deems as 'manlier'. "A magical birthday gorilla."

By the time the others arrive at Cosette's house to pick up Marius, Cosette and Eponine, Marius has decided that now is the right time to have a meltdown over the fact that he has university exams in little over a week. Mid-panic, he declares desperately that he's not coming and proceeds to bury himself in sheets of paper and books. Cosette and Eponine take care to quickly slip out of the house and into the back seat of the car with Feuilly, quickly avoiding the (teary) wrath of a stressed Marius.

"Drive, drive, drive!" Eponine jokes. "Before he starts wailing."

"He chooses the worst times to have a freak out, doesn't he?" Cosette shakes her head. "Best to just leave him be, isn't it?"

"I love how Marius and Enjolras are the only two that actually even care about these tests," Bossuet shakes his head, giggling. "Joly texted, Enjolras isn't coming."

"Aw that sucks," Feuilly sighs. "I like Enjolras' company."

"Has Bahorel's driving killed them yet?" Eponine grins.

"Nope, but Joly almost puked."

"No wonder. It's like he's playing Mario Kart in real life," Grantaire laughs.

"More like Grand Theft Auto," Cosette adds, earning fits of laughter from the rest of the group.

Thankfully, Grantaire's driving is much calmer compared to Bahorel's, and his friends feel safe in his car. They come towards the give-way sign where they're expecting Bahorel's car to pass by any second. It doesn't. Grantaire takes one last look at the empty road and puts his foot down on the accelerator. But Bahorel's car appears, as he presses the accelerator a little more than he should.

He's moving so fast that he still thinks Grantaire's car is still. It's not. It drives full force into the side of his car.

And everything goes black.