AO organizers add lot of sand into surface to slow it down
Hard courts are made of uniform rigid material, offering greater consistency of bounce than other outdoor surfaces. Hard courts can vary in speed, although they are faster than clay but not as fast as grass courts. The quantity of sand added to the paint can greatly affect the rate at which the ball slows down. Hard courts are generally more equalizing than clay or grass in terms of playing style, although they favor harder-hitting baseliners and all-court styles with the current equipment. The US Open is played on an acrylic hard court, while the Australian Open is played on a synthetic hard court. The main difference between a synthetic hard court and a true hard court surface is the level of hardness. When the ball bounces on this surface it is faster than all other surfaces if there is not much sand in the top paint. The amount of sand used in the top paint and the size of the sand also determines the speed – more sand means less speed and larger sand particles will slow the speed of play. The amount of friction can also be altered and more friction will produce a clay court effect, where topspin is magnified. The extra grip and friction will resist the sliding effect of the ball and the resistance will force the ball to change its rotation. Although hard courts are the least expensive to maintain, they are generally more rough on the human body than other surfaces due to their rigidity.