Physics of 'the Hit'

redout

Right lads, I thought that this would make an interesting read considering some of the tackles which we have been seeing over the past year. They seem to be getting more dangerous all the time. Its more to do with the physics side and just take out the whole NFL thing.





Julie Jacobson/Associated Press
Baltimore running back Willis McGahee was knocked unconscious after a collision with the Steelers' Ryan Clark in the A.F.C. championship game.


A head-on hit from the Jets’ Eric Smith sent the Cardinals’ Anquan Boldin to the hospital.




Clark’s shockingly violent hit on the Baltimore Ravens’ Willis McGahee two Sundays ago — a full-speed, helmet-to-helmet crash that left McGahee unconscious and Clark all but — didn’t just follow the N.F.L.’s rules, but Newton’s as well. Force equaled mass times acceleration. Momentum was conserved. And the bodies finally came to rest, McGahee’s on a stretcher.
“How I look at it, you can be the hammer or the nail,” the inner scientist in Clark explained this week. “I try to be the hammer.”

The tackle, the art of making the ball carrier not stay in motion, is football’s most primeval action. Amusing physicists the way batting averages do actuaries, collisions lead the highlight reels, impart the force of a deadly car crash, and rely upon kinematics that date to a considerably different big bang.

Sunday’s Super Bowl could very well ride on how well the Steelers’ defense — known as perhaps the most fearsome and bone-clattering in the N.F.L. — can tackle the Arizona Cardinals’ fast and evasive wide receivers. From angles and acceleration to speed and centers of gravity, players might not understand the physics of tackling, but they know how to wield it.

“It’s all about timing and leverage,” Cardinals safety Adrian Wilson said. “Being able to time the hit the right way, and the leverage you’ve got to have once you make impact so the other player goes back, and not you.”
Trying to trip up or throw down a ball carrier with only one’s arms can be a risky maneuver. Barreling straight into him with 200-plus pounds of muscle at 20 miles an hour is a more reliable impediment.

From there, Newton’s second law of motion (force equals mass times acceleration) and conservation of momentum take over. Mass is the players’ weight, which in the N.F.L. grows higher every decade.

Acceleration is not that of the incoming tackler, as is often assumed, but how quickly both the defender and runner slow down through impact.
It is this duration of impact, between one- and two-tenths of a second by many estimates, that has tremendous effect on the force of a football collision. Hard objects repel each other quickly; equally heavy but softer objects have “give” that allows their contact to last longer and accept the force less jarringly. It’s the difference between being hit by a baseball and being hit by an overripe peach.

“The tackler doesn’t want his body to be a big spring — these players lower their shoulder and tense up and launch to make their force go up,” said Stefan Duma, a professor of mechanical engineering at Virginia Tech who has studied the similarities between football collisions and car crashes. “It’s like trying to break down a door — you try to get all your mass behind you and drive it through one point. You want to get all your mass to act as one mass, one missile.”

Reaching the ball carrier at full speed is crucial, as any deceleration before impact saps force from the hit. This is where angles come in, said Timothy Gay, a professor of physics at the University of Nebraska-Lincoln and the author of “Football Physics: The Science of the Game.” Football instincts allow the best safeties to anticipate where the runner or receiver will be and then take the shortest route to him, maintaining speed and even allowing for one final push.

“Jack Tatum was vicious — that helps — but he had a way of popping with the perfect angle and timing,” Gay said of the former Oakland Raiders safety called the Assassin in both reverence and fear. “The best hitters accelerate at the last instant. That final jolt of speed allows them to apply a bigger force to their victim.”

Ask a physicist and a coach where that force should be applied, and they can answer differently. Gay said that the hit should be applied at the runner’s center of mass — just below the rib cage in the center of the chest — to direct all the force into stopping his forward motion. Missing that spot by too much, Gay said, “Causes the ball carrier to rotate around his center of mass, and he might not go down. The announcer would say, ‘He bounced off him.’ ”

But Ray Horton, the Steelers’ defensive backs coach, preaches a different approach. He is all for the ball carrier rotating, as long as he does so violently enough to wind up on the turf.

“We teach you tackle at the knees — if you tackle at the thigh to the shoulders, that’s his power box,” Horton said. “If I want something to tip over, I don’t want to hit it in its center of gravity, because it might go straight back and stay upright. If I want it to go down, I want to hit below the center of gravity, and that’s why we hit by the knees.”
Horton added: “Low man wins. If you hit him too high, he’s going to run you over because of the physics of how big these guys are.”

One Cold Hand

What has this got to do with soccer?

therecklessone

One Cold Hand wrote: »

What has this got to do with soccer?

I'm inclined to agree. I'll wait and see if anyone can draw parallels to tackling in the soccer though

eagle eye

therecklessone wrote: »

I'm inclined to agree. I'll wait and see if anyone can draw parallels to tackling in the soccer though

You're wish is my command.:)

iregk

Most people skip over large posts at the best of times. When the large post has in fact nothing what so ever to do with soccer, in the soccer forum then meh!

Most useless thread ever!

_blank_

...and what does Eric Cantona jumping the fence to launch into a fan have to do with tackling on a football pitch?

therecklessone

Des wrote: »

...and what does Eric Cantona jumping the fence to launch into a fan have to do with tackling on a football pitch?

Nothing.

Thread closed, if anyone can think of a good reason why this belongs on the Soccer Forum send me a PM and I'll reopen.