Skeleton involves a person riding a small sled down a frozen track while lying face down. The sport is a more intense form of luge because skeleton competitors leap onto the sled and slide downhill head first. Skeleton athletes can reach up to 80 mph on straightaways, causing forces up to 5g, so the helmet is a critical component for attitude as well as safety.

A mass pillow fight in Trafalgar Square in central London on April 5, 2014 on International Pillow Fight Day. (Photo by Jane Scanlan)

The competition, which is run by the Royal Observatory Greenwich in association with BBC Sky at Night Magazine, is now in its sixth year and has received over 2,500 entries. Photo: Centre of the Heart Nebula by Ivan Eder (Hungary). Situated 7500 light years away in the “W”-shaped constellation of Cassiopeia, the Heart Nebula is a vast region of glowing gas, energized by a cluster of young stars at its centre. The image depicts the central region, where dust clouds are being eroded and moulded into rugged shapes by the searing cosmic radiation. (Photo by Ivan Eder)

In a January 19, 2014 photo Phillip Seymour Hoffman poses for a portrait at The Collective and Gibson Lounge Powered by CEG, during the Sundance Film Festival in Park City, Utah. Hoffman, who won the Oscar for best actor in 2006 for his portrayal of writer Truman Capote in “Capote” was found dead Sunday in his apartment in New York with what law enforcement officials said was a syringe in his arm. He was 46. (Photo by Victoria Will/AP Photo/Invision)

Rihanna celebrates by flashing the crowd on July 13, 2014 in Rio de Janeiro, Brazil. (Photo by Twitter.com)

Model Isabeli Fontana poses after the 2014 Victoria's Secret Fashion Show in London December 2, 2014. (Photo by Luke MacGregor/Reuters)

Hot air balloons fly over the sky in Chiang Mai province, northern Thailand, December 6, 2014. The two-day International Balloon festival 2014 featuring balloon pilots from Germany, Spain, Netherlands, Britain, and Czech Republic is held on December 06-07 2014 to celebrate Thai King Bhumibol Adulyadej's 87th birthday and also aimed to promote the tourism industry in Chiang Mai northern city. (Photo by Pongmanat Tasiri/EPA)

Two 70 thousand RMB (about 11,310 USD) robots carry dishes and offer service for customers at a robot themed restaurant at Chunxi Road in Chengdu, China, December 11, 2014. The restaurant has 10 robots to serve as waiters. Each robot can carry simple dishes and offer simple greetings. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)