LESTER HOLT reporting: Whether it’s a running back breaking through the secondary or a wide receiver on a foot race for the end zone, most offensive players in the NFL have a single goal in mind–to get down-field as far and as fast as possible. ANTONIO FREEMAN (Former NFL Wide Receiver): We’re thinking, wow, I’ve got to get from A to B within a certain time frame and I can’t let this guy throw me off track. So it’s kind of like a chess match at that point in time is to battle to see who’s the toughest. HOLT: Defenders on the other hand have a different goal– to stand in the way of the offensive player and stop his forward progress. HARDY NICKERSON (Former NFL Linebacker): When you are coming in and making the tackle, you’ve got to come in and you got to stop him right there on the dime. HOLT: Who wins this epic battle between the ball carrier and the defender? Newton’s First Law of Motion helps supply some answers. TONY SCHMITZ (University of Florida): Newton’s First Law says that if an object is at rest it requires an unbalanced force to make it not be at rest or similarly, if an object is in motion, it tends to stay in motion in a straight line at a constant velocity unless an unbalanced force acts on it. HOLT: In football, we see unbalanced forces whenever one player exerts a force on another and causes him to change his direction and/or speed. JIM GATES (University of Maryland): So, imagine that a quarterback is just taking the snap from the center and a lineman gets free from the opposing team and is coming from the other side and–when they collide, you can see an unbalanced force acting on the quarterback, driving him across the field in the direction of the charging lineman. That’s about as unbalanced as it gets. HOLT: In physics, a player’s natural resistance to that unbalanced force is something called “inertia.” SCHMITZ: On the football field you can think about inertia as being a running back who is already in motion doesn’t want to change the fact that it’s already in motion. So, it’s going to take some external unbalanced force, i.e., a defensive player to stop that running back. HOLT: Consider former New Orleans Saints running back Deuce McCallister, who at 6-foot-1, 231-pounds used his inertia when running to make him hard to tackle. SCHMITZ: The size of the player is important to a concept of inertia because higher mass means more inertia. HOLT: But a player’s mass is different from his weight. Mass is a measure of how much matter an object has while weight is a measure of how strongly an object’s mass is attracted by gravity. SCHMITZ: So, for example, a body on earth would have the same mass as that body on the moon. but it would weigh less on the moon because gravity is less on the moon than it is on earth. HOLT: NFL players with more mass have more inertia, and are harder to move off their path. This concept even works on a quarterback sneak, when a quarterback uses the combined mass of his entire offensive line to gain a yard or two. JOEY HARRINGTON (Former NFL Quarterback): If you got an offensive line that can overpower the defensive line, that’s just get on their hip and you just fall, I mean, you just ride that wave forward. HOLT: In the NFL, whenever players go head to head it’s Newton’s First Law of Motion that helps determine who will win the battle of the gridiron.