Ajayi's touchdown run was so fun to analyze that I decided to write a bit more in my blog post. Linear momentum, forces, and the laws of physics played crucial roles in the touchdown, like they do in most everything else that happens in the world. Look at the screen capture below for the start of the play (click on the image for a larger view).
The Eagles have 1st and 10 at the Broncos' 46-yard line. Quarterback Carson Wentz is in the shotgun and Ajayi is lined up on Wentz's right. Note there are four defensive lineman and five offensive lineman. Eagles' center Jason Kelce is not lined up against anyone. Kelce is about to play a major role in the play with some key blocking. Before that, he had to snap the ball to Wentz. The ball took about 0.4 s to reach Wentz, which is about the time it takes for a major-league fastball to reach home plate. Once he snapped the ball, Kelce pulled to his left, Ajayi took two strides to his left to receive the ball from Wentz, and then he witnessed the most beautiful blocking open up before him. Check out the blocking in the image below (click on the image for a larger view).
Eagles' left tackle Halapoulivaati Vaitai had Broncos' outside linebacker Shane Ray (#56) blocked. See the yellow circle in the above screen capture. Eagles' left guard Stefen Wisniewski had Bronco's defensive end Shelby Harris taken care of. See the orange circle in the above image. Look at the hole Ajayi is about to run through! After getting the ball from Wentz, Ajayi needed just five strides to get to the hole. Note the white arrow on lead blocker in the hole, center Jason Kelce. He has his eyes on Broncos' strong safety Justin Simmons. Take a look at the blocking scheme from another view (click on the image below for a larger view).
That's quite a hole, right? The Eagles' lineman employed their intuitive physics knowledge of linear momentum to set up the great run. Isaac Newton taught us that a net, external force is needed to change an object's linear momentum. The product of an object's mass times its velocity is an object's linear momentum. Beefy lineman have lots of mass and thus need lots of force to stop. A couple hundred pounds of force to stop a defensive lineman are not out of the ordinary. Offensive lineman intuitively know that linear momentum and force are vectors, which means they have directions as well as magnitudes. Keep that in mind for the end of the play.
The great line blocking allowed Ajayi to hit the hole at a speed of about 19 mph (31 kph). He was able to maintain that speed while running down the left sideline. While running toward the goal line, Ajayi's linear momentum was pointed right at the goal line. Broncos' free safety Darian Stewart was Denver's last hope on the play. Unfortunately for Stewart and Denver, linear momentum was working against them. Check out the screen capture below as Stewart hit Ajayi at the Broncos' 3-yard line, just below Ajayi's hip (click on the image for a larger view).
Stewart hit Ajayi with a force nearly perpendicular to Ajayi's linear momentum. That certainly changed Ajayi's linear momentum, but mostly perpendicular to the left sideline. Despite a force of several hundred pounds over less than 0.1 s, Ajayi's linear momentum change was mostly toward the out-of-bounds area. That works great unless an athlete like Jay Ajayi is a couple yards from glory and he is able to contort his body. He still had much of his linear momentum that was pointed toward the goal line after the hit.
Just as he was hit, Ajayi rotated toward his right. That ensured that after he was hit, his ball-carrying left arm would be above his body and ready to pass over the orange pylon for a touchdown. See what I mean in the screen capture below (click on the image for a larger view).
From the terrific blocking at the start of the play to Ajayi's contorted body over the pylon, linear momentum was the 12th man on the field for the Eagles!
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