NBC's Lester Holt looks at how the physics concepts of torque and center of mass are applied in football by some of the games most massive players -- the offensive linemen. "Science of NFL Football" is a 10-part video series funded by the National Science Foundation and produced in partnership with the National Football League.
Science of NFL Football - Torque & Center of Mass
LESTER HOLT, reporting:
In a game played by big men, NFL offensive linemen are some of the biggest of all. Whether they're blocking for a running back or protecting the quarterback, these giants of the O-line know how to use size to their advantage.
ORLANDO PACE (Former NFL Tackle): Man there's some big guy’s that play in NFL, especially on the defensive line. So sometimes those big guys just hit and, you know, other big guys and you're trying to move and low man really wins.
HOLT: Who wins the battle of the gridiron goliaths? According to the laws of physics, it's the player who stays the lowest and masters the concept of torque - which is the tendency of a force to make an object rotate around an axis.
Dr. JIM GATES (University of Maryland): A torque is anything that causes another object to spin.
HOLT: In the NFL, we see torque whenever one player collides with another, causing him to rotate or spin. What's key is the distance of the force from the rotation axis - this distance is called the "lever" or "moment arm."
Dr. JIM GATES (University of Maryland): So where the force is applied to an object determines whether there's a torque. If I hit dead on, no torque, if I hit a little bit to the side and cause spinning, I have a torque.
HOLT: To counter this rotational force, coaches at all levels teach players to stay as low as possible.
TONY SCHMITZ (University of Florida): Get low, get low now.
HOLT: Tony Schmitz is a former Division One college football player and currently a coach for the Newberry High School football team, but as a mechanical and aerospace engineer at the University of Florida, he understands the physics behind staying low.
SCHMITZ: Coaches often talk to players about staying low and there is different phrases they use like the low man wins, because if I can have my center of mass low and exert my force against somebody with their center of mass high, I'm more likely to push that person over and win the battle.
HOLT: A player's center of mass, often referred to as their center of gravity, is the point on a body where mass is most concentrated.
SCHMITZ: So the center of mass is the average location of mass for any body. For a lineman, for example, that center of mass is usually somewhere near the navel.
HOLT: When a player crouches, his center of mass is lowered.
Dr. GATES: And that's one reason you want to stay low because, if you're low, you're taking advantage of the laws of physics that says that if you can't get to my center of mass, it's hard for you to make me rotate.
PACE: The low man wins on this one, that's the key.
HOLT: Consider Orlando Pace, 7-time Pro Bowl offensive tackle with the St. Louis Rams who stands 6 foot 7, 325 pounds. His center of mass is located just above his hips. By crouching, Pace not only lowers his center of mass but he's now in a position to impart a bigger torque because he's able to hit upward on his opponent.
SCHMITZ: By hitting on the rise we can actually increase the torque that we applied to a body because as we start low there is a low moment arm from where we apply the force to the ground, but as we get higher that moment arm increases and we are applying more torque.
HOLT: As Pace rises from the crouched position, the distance between his opponent's pivot point and the location where Pace applies the force increases, allowing him to impart a higher torque on his opponent.
PACE: To move a guy off the line against his will is probably the biggest thing, biggest success as an offensive linemen you can do because that guy is trying to come forward, you're moving him back, as an offensive lineman that's our touchdown.
HOLT: And in a game where the low man wins, that success comes one push at a time.
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