Why do slalom skiers hit the gates?
There's no rule in slalom or giant slalom that you have to hit those gates, but you have to pass between them on alternating sides, with both skis' tips passing between the poles. The closer you get to the gate, the more direct route you're taking down the slope -- which means a faster runtime. If you're getting your skis right next to the gate, you'll have to hit it with your arm or shin and knock it down. That's part of the reason skiers wear helmets with visors and guards on their shins and arms. Each skier takes two runs, and the times from these are added up. Because these often come down to split-second victories, hitting the gate or not can make all the difference in taking home a gold medal.
How long is a slalom course?
For men's slalom, the course at PyeongChang is 575 meters and the women's course is 556 meters. For men's giant slalom, the course is 1,326 meters and women's is 1,250m. Skiers are racing downhill with a formidable vertical drop, often between, 591 and 722 feet. The gates are set up to make shifting between them difficult and as skiers navigate the course they appear to snake through it.
How fast do slalom skiers go?
Giant slalom skiers tend to hit an average of 25mph. Skiers tend to go even faster in standard slalom because the gates are closer together and the line is more direct. These high speeds also make falls particularly dangerous and when combined with high winds like at this Olympics, the risk of injury is high, particularly for knee injuries.