Newton’s Second Law of Motion – Science of NFL Football

LESTER HOLT reporting: To be an NFL kicker takes more than just nerves of steel and a strong leg. It also requires help from one of the key laws of physics. MORTEN ANDERSEN (Former NFL Kicker): It’s easy to say, well, I just kicked the ball. Well, let’s delve into it. Let’s look at the specifics. What actually happens when you kick the ball and why does the ball go where you ask it to go–and it is Newton’s Second Law–Second Law of Motion. HOLT: The Second Law is one of three laws described in 1687 by Sir Isaac Newton, who used them to describe how and why objects move. JIM GATES (University of Maryland): The Second Law says that if you have an object with a mass that is accelerating–and accelerating means a change in velocity–that is equal to the amount of force applied to the object. The way we say it with words is F is equal to MA. HOLT: This also means that in order for an object, like a football, to accelerate, a force must be applied. To illustrate Newton’s Second Law in kicking, we asked Morten Andersen, the NFL’s all-time scoring leader, to perform his craft in front of a high-speed Phantom camera. The entire procedure unfolds in less than a second-and-a-half, from snap … to hold … to kick. ANDERSEN: It’s all about training and rehearsing and doing something over and over and over again. HOLT: To reduce the chance of a block, NFL kickers take just three steps to the ball. The final step is with the plant foot, which provides the stable platform for the kick. ANDERSEN: I call it the moment of truth and the moment of truth is basically when your plant foot hits the ground next to the ball. You’re either in the right position or the wrong position. 
HOLT: The kick, itself, involves the entire leg building the force necessary to launch the football. ANDERSEN: It’s a hammer, and when you swing a hammer, you’re thrusting it and it’s going to be impacting the ball with great velocity. HOLT: An NFL kicker’s foot is in contact with the ball for just 8-one-thousandths of a second–and in that time, his foot applies up to a ton of force to the ball. This quick, violent strike is a perfect example of what’s known in physics as an “impulse.” SCHMITZ: Impulse is an important concept because there is a finite time over which the foot is in contact with the ball, and during that time there is a force applied to the football. HOLT: An impulse is equal to the force multiplied by the time the force is applied, represented by delta-T. If force is graphed versus time, it’s possible to see how a larger force, or a longer time for the force, supplies a bigger impulse. GATES: Since impulse is really just the change in momentum and since the ball doesn’t change it’s mass, we’re really just talking about the change in speed. The bigger the impulse, the bigger the change in speed, which means the faster the ball is moving after it leaves the kicker’s foot. HOLT: Ironically, Andersen says the distance of the field goal doesn’t change his approach to the kick, itself. ANDERSEN: Mentally, you want to look at a fifty plus yarder like a forty yarder with some room to spare. I think that’s a good way to kind of fool yourself into thinking it’s a shorter kick. HOLT: Whether the kick is short or long, Newton’s Second Law explains what an NFL kicker must do to send a football through the uprights.

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