Ponca City, We Love You writes "There will be a program on applied physics and real time strategy that you might want to watch on television today and conservation of momentum in elastic and inelastic collisions is one aspect to focus on as players tackle their opponents. It is of critical importance that the Patriots bring down New York's huge and powerful running back, 6-foot-4, 265-pound Brandon Jacobs. The problem is that nobody seems to put their arms around a ball carrier any more when they make a tackle. Rather than haul ball carriers to the ground, defenders prefer to cut the feet out from under them. They want to block them, not tackle them. An average-size NFL defensive back's mass combined with his speed — on average, 4.56 seconds for the 40-yard dash — can produce up to 1600 pounds of tackling force. A tackle with half a ton of force may sound like a crippling blow but the body can handle twice that amount because the player's equipment spreads out the incoming energy, lessening its severity. Instead of taking the opportunity to put some hurt on a ball carrier, defenders sometimes seem more worried about getting hurt themselves and so protect their arms and shoulders. "I know you can tackle better," says Joe Collier, who played linebacker at Northern Colorado, "if your arms are around the guy.""