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Why do Daytona 500 drivers tailgate at 200 mph? Physics.

Chris Graythen/Getty Images
Brian Resnick is Vox’s science and health editor, and is the co-creator of Unexplainable, Vox's podcast about unanswered questions in science. Previously, Brian was a reporter at Vox and at National Journal.

NASCAR is ridiculous. At the Daytona 500 in Florida this weekend, souped-up cars will chase each other around a 2.5-mile track at speeds approaching 200 mph. They'll do this for 200 laps, for a total distance of 500 miles.

But this is what's truly crazy: For much of the race, the cars will be just inches apart from one another.

(Robert Laberge/Getty Images)

This amps up the drama of the sport. But the drivers do it for another reason: It helps them go faster.

Here's why.

Driving is a drag

A car driving in a forward direction is slowed down by two forces:

1) The friction of the air in front of the car

Anything that moves forward has to push air out of the way. That air pushes backward on the car, resulting in drag, diminishing the car's top speed. (This is the idea behind Elon Musk's Hyperloop. A vacuum tube has no air, and therefore no drag, which would allow Hyperloop trains to reach extremely high speeds efficiently.)

2) The wake of turbulent air created by the back of the car

The forward motion of the car creates an area of lower pressure behind the vehicle. This acts like a vacuum behind the car, pulling it backward as the vehicle accelerates forward.

When two cars come within inches of one another — in a move called drafting — both problems are solved

The front car blocks the oncoming wind for the second car, and the second car blocks the trailing turbulence of the first.

"When two cars get close enough, air flows around them as if they were a single car," Diandra Leslie-Pelecky, a physicist, says in the National Science Foundation video below. "This decreases the total amount of drag on the two cars."

These two cars can then go 3 to 5 miles per hour faster than they could on their own. Research from Cornell suggests that the front car may actually receive the greater benefit of aerodynamic efficiency.

"It's hard to explain to you guys that aren't in cars, but when there's someone directly behind you and they pull their car out of line really fast, it's like you pull a parachute in your car," NASCAR driver Jamie McMurray described in a 2010 interview with "It literally feels like you lose three or five miles an hour immediately, and when that happens, the car that's doing the passing just has the momentum."

Cars can't draft for the entire race: The trailing cars' engines overheat more quickly in this configuration because of the diminished airflow. So drafting and deciding when to pass involves a lot of strategy.

Drafting is especially important at Daytona 500. Rules of the track stipulate that cars must use restrictor plates on their engines to intentionally slow the cars down — this is a safety measure. Because cars are not performing at their top level, drafting allows drivers to get a bit more performance out of their cars, which just might make the difference for a win.

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