Well class, it saddens me to say that our time for the semester is coming to an end, as this will be our last lecture.

I have graded all the midterms, and they turned out great. If you put the same amount of effort into the final you should be just fine.

I know we began the semester by examining football, but I thought we would return to the sport one more time since the NIU football team is heading to the Poinsettia Bowl.

So with that, today we will be exploring the physics of tackling.

To begin, let’s set out some basic principles needed to understand what is going on.

A tackle is an example of applying a force to a body. A force is simply something that influences the motion of an object — a pushing or pulling.

The amount of force is determined by the mass and acceleration of the object causing that force. Mass is just the amount of “stuff” an object is made of. Acceleration is how quickly the object is changing its velocity.

NIU defensive end Larry English understands that his acceleration is key when he goes to tackle an opponent.

“For the most part with a tackle, all I do is run full-speed at them,” English said. “And, at the point of collision, you sink your hips a little bit, throw your arms into them and wrap them up.”

English’s speed provides a great deal of acceleration on an offensive player who is moving slower than him. But tackling is not only running and hitting; aim is also important.

“You obviously want to stay lower than him and get underneath him,” NIU middle linebacker Tim McCarthy said. “It’s not good to aim too low, though, because otherwise they’ll jump over you or avoid you.”

So why aim low?

The answer is all in rotation. Your body’s center of mass is in the torso, and a tackler can take advantage of this.

Rotating a body requires less force than pushing directly at its center of gravity to stop it. Aiming low uses the opponent’s forward motion to help rotate the body. This method doesn’t stop the opponent’s motion, but redirects his center of mass.

“You are turning his translation [forward] motion into rotational motion so he rotates to the ground,” associate physics professor Larry Lurio said. “Therefore, you have to worry about your torque around his center of mass.”

Torque on a player, a rotational force, is the amount of horizontal force multiplied by the distance from the center of mass at which the force is applied.

Therefore, more torque is generated if a tackle is aimed lower because of the greater distance from the center of mass. Likewise, applying a greater force at a lower position generates greater torque.

In theory, it is best to tackle at the feet. But, as McCarthy pointed out, such a low tackle gives your opponent a greater chance to escape. Aiming for the thigh area tends to maximize the probability of catching an opponent while still providing a lot of torque.

Finally, wrapping up the opponent as you tackle is key to preventing them from breaking out of the tackle.

We are out of time for today’s class. ‘Til next time, be safe and enjoy the break.

Ben Gross is a Sports Reporter for the Northern Star.