It's about 1,500 times as heavy as a Football (American).
In other words, 521 kilograms is 1,267.4299431540 times the weight of a Football (American), and the weight of a Football (American) is 0.0007889982443617 times that amount.(a.k.a. "pigskin") (NFL standard)
Per National Football League official rules, an American football must weigh between 0.396893323750 kilograms and 0.4252428468750 kilograms. Because of NFL regulations, ceremonial considerations, and backup requirements, each NFL Superbowl requires the manufacture of 144 balls exclusively for the event.
It's about 1,500 times as heavy as a Can of Soup.
In other words, the weight of a Can of Soup is 0.00067 times 521 kilograms.(for Campbell''s Condensed Tomato Soup, 317.9 ml)
A can of Campbell''s Tomato Soup weighs 0.350 kilograms. Cans have been used to store soup and other foods since their invention in 1913, but a dedicated can opener was not developed until cans began to use thinner materials — prior to that time, cans were usually opened using various blunt instruments and tools.
It's about 1,500 times as heavy as a Human Heart.
It's about 3,000 times as heavy as a Hamster.
In other words, the weight of a Hamster is 0.0003 times 521 kilograms.(for Syrian hamster, a.k.a. golden hamster, a.k.a. Mesocricetus auratus; adult)
An adult Syrian hamster has a typical weight of about 0.20 kilograms. Known for transporting food in the pouches of their cheeks so that they can bury it later, some hamsters can store up to 25 kg of food in their borrows.
It's about 3,000 times as heavy as a Billiard Ball.
In other words, 521 kilograms is 3,196.12768273590 times the weight of a Billiard Ball, and the weight of a Billiard Ball is 0.00031287861414347 times that amount.(American-style, WPA specifications)
Per the World Pool-Billiard Association, a billiard ball weight must weigh between 0.15592237718750 kilograms and 0.170097138750 kilograms. According to legend, the difficulty in obtaining elephant ivory for the manufacture of billiard balls in the 19th century inspired the search for a replacement material, which led to the development of the first industrial plastic.
It's about 3,000 times as heavy as a Puck (Hockey).
In other words, 521 kilograms is 3,196.12768273590 times the weight of a Puck (Hockey), and the weight of a Puck (Hockey) is 0.00031287861414347 times that amount.(Ice hockey)
A standard ice hockey puck weighs between 0.15592237718750 kilograms and 0.170097138750 kilograms. Hockey pucks can be shot or passed at speeds of up to 160 kph (99 mph) during games.
It's about 3,500 times as heavy as a Baseball.
In other words, 521 kilograms is 3,585.89935136220 times the weight of a Baseball, and the weight of a Baseball is 0.00027887006912788 times that amount.(MLB rules)
Per Major League Baseball rules, a baseball must weigh between 0.1417476156250 kilograms and 0.148834996406250 kilograms. A major league pitcher can throw a baseball at up to 150 kph (91 mph) (with a fastball pitch), with record-setting pitches as fast as 171 kph (106 mph).