I am a Physics Ninja, Part Two

Many of the contestants on the American spinoff of Ninja Warrior are avid participants in parkour. To these traceurs (and  yes, I did need Google to learn that word), the whole world is an obstacle course. To nerds, the whole world is a science demonstration. This is the second in a series of posts that shows what happens when these two worlds collide.

2) Newton’s Second Law: The acceleration of an object is inversely proportional to the mass of the object and directly proportional to the net force applied to the object. Mathematically, this is expressed as Force=mass x acceleration. The less mass an object has, the easier it is to get it to speed up. If you push harder, you’ll speed the object up more.

This is probably the most intuitive of Newton’s Laws, and commentators have referred to it (if not by name) on both Wipeout and Ninja Warrior.A recent Wipeout episode featured a course that began with a contestant lying down on one end of a giant airbag. A huge block of metal was dropped onto the other end, launching the contestant high into the air. The faster a contestant went, the higher she would get before the force of gravity pulled her into the water. Since the same force was applied every time, the acceleration (and thus maximum speed and maximum height) that each contestant achieved was dependent only on her mass. This means that the least massive contestant flew the highest, a relationship that was noted by one of the show’s commentators. I would’ve squealed with joy had he called out Newton’s Second Law by name, but hey, I’ll take non-specific scientific references over none at all.

Newton’s Second Law also comes into play when discussing human-strength-to-weight ratio. On Ninja Warrior, many obstacles require contestants to support their entire body weight using only their arms. To avoid falling, their arms have to exert an upward force that is at least equal in magnitude to the downward force of their weight. Since weight is the force on an object due to Earth’s gravity, and, barring air resistance, all objects accelerate toward Earth at the same rate, the upward force that each contestant must exert is directly proportional to his mass.

This is why strength-to-weight ratio is so important, and it’s a point that American Ninja Warrior commentators have discussed. A burly, muscular contestant could actually be at a disadvantage on these types of obstacles. He could be capable of exerting one-and-a-half times the force that a leaner contestant was capable of, but if Mr. Muscle is actually twice as massive, the leaner contestant will still be more successful.

The final installment of this series will discuss how Newton’s Third Law of Motion relates to Wipeout and Ninja Warrior. It may also make you start saying “push-downs” instead of “push-ups.”

PS: You may have noticed that I try to say things like “less massive” and “twice as massive” instead of “lighter” and “heavier.”  The explanation behind this is definitely going to be the focus of a coming post.


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