F1 cars spark due to titanium that is embedded within skid plates that are installed underneath the cars themselves.
F1 cars are mandated by the FIA (essentially the authority on motorsport rules and regulations) to have skid plates on their undersides. These are constructed from wood, and the titanium is added and extends outward from the wood itself. The plates are required by the FIA in order to ensure all cars are at the proper ride height and reduce ground effects.
Ground effects essentially help the vehicle stay planted to the ground by way of downforce. This can be used to increase overall handling and driving performance, which is why F1 cars utilize the skid plates to limit the amount of advantage drivers can have by exploiting said ground effects.
Since 1994, the FIA has required F1 drivers to install a 10-millimeter-thick plank, and the plank cannot wear down by more than 1 millimeter. If it does, that driver is disqualified and can no longer compete.
This might seem a bit dramatic, as 1 millimeter is not much, but this is all to keep the competition as equal as possible. Vehicles must conform to the required height and be unable to gain an advantage due to ground effects that other drivers would not have.
Technically, the use of titanium that extends beyond the surface of the wood is a workaround the drivers used to lessen their chances of disqualification due to plank wear, as well as circumvent the ride height limitation, because the titanium extends beyond the lowest point of the vehicle's underside and the attached wood plank!
Interestingly, although the overall purpose of the planks are to prevent the aforementioned advantages, it was also in the hopes of reducing the amount and level of sparks caused by the undersides of the already very low to the ground F1 cars touching the track.
Lukas Raich, CC BY-SA 4.0, via Wikimedia Commons
If the wooden skid plate is worn down even a very small amount (as noted above), the driver will be disqualified from a race. To avoid damage via contact with the ground, titanium is added that extends beyond the wood by approximately 3 millimeters, ensuring that when contact is made, the titanium will be worn and leave the wood intact.
This practice helps maintain the integrity of the skid plate and reduces the chances of disqualifying due to plate wear, which is why the practice is commonplace with F1 cars.
When titanium makes contact with the ground, sparks can be seen, usually appearing white in color. The reason for the sparks is chemistry: Titanium reacts with the air when heated. This is often demonstrate by grinding a piece of titanium until it begins to spark.
The friction, and thus heat, generated from the titanium scraping across the track at high speeds is what causes the sparks to occur.
Physics is the answer here. When an F1 car is moving at high speeds, as it does, aerodynamics ensue and the car is pushed toward the ground. This is what is commonly referred to as downforce. Obviously, because the titanium is intentionally installed to be the part of the vehicle lowest to the track, it will be the portion that hits the ground and leads to sparks.
F1 cars are engineered in such a way as to maximize their aerodynamic performance, explaining why they have the shape they do. This is what enables them to effectively be pushed further into the ground while at high speeds.
So we know that when the titanium touches the track, sparks will start flying from under the car, creating quite the spectacle for the audience who might think it is a sign the car is damaged or is being damaged. After all, there will literally be a line of sparks trailing from under the vehicle, which certainly appears like severe damage is happening!
Counterintuitively, the sparks mean the titanium is doing its job of protecting the wood plank and the general underbody of the car, keeping the driver safe and qualified to compete. This is because it is not the actual vehicle causing the sparks, but an attachment of sorts in the form of titanium.
Granted, if the actual underbody of the F1 car was to touch the ground and create sparks, it would be reasonable to suspect true damage was occurring because the metal contact would be from the chassis itself. This is not the case today though with current FIA rules, as F1 cars do not take to the track without the added skid plate.
No! Skid plate requirements were introduced and drivers used other metals to supplement their planks (although during the 1980s and 1990s, competitors did indeed use titanium). However, this proved to be dangerous because these other metals would sometimes break off on the track, creating a hazard for the drivers and their cars.
To remedy this problem, the FIA required titanium to be used as of 2015 as it is a strong metal that is less likely to break off on the track and cause trouble.
The sparks are an unavoidable aspect of using titanium, knowing full well that said titanium will lead to sparks when it inevitably slides across the ground.
Although it was for safety reasons that other metals were essentially banned from F1, there was also an entertainment factor to consider. Sparks are exciting and help make an action-packed motorsports event all the more interesting to watch. They might be an unavoidable outcome, but they definitely do not seem to hurt F1's popularity, with cars providing their own bit of fireworks on the track as they push ahead at a blisteringly fast pace.