Jack Reacher's Physics Explained by Dr. Alan Ritchson
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Chapter 1: Introduction to Jack Reacher's Physics
How can Amazon promote the latest season of Jack Reacher? A brief video featuring Alan Ritchson discussing some physics concepts could be an excellent approach. Check it out below.
While the video is entertaining, I feel compelled to provide a professional physics analysis. Here are some points to consider, along with my recommendations for improvement.
Section 1.1: Breaking a Zip Tie
Alan asserts that he successfully broke a zip tie that was securing his hands. Given his physique, I have no doubt he's being truthful. The video suggests that it requires 120 pounds of force to snap a zip tie. While I won't verify this experimentally, it's known that zip ties vary in size, making this figure plausible.
It's important to note the use of “pounds of force.” This is tailored for a U.S. audience, so the term “force” is added to clarify that it's not a weight measurement. Personally, I prefer using Newtons, where 1 pound equals approximately 4.45 Newtons. Nonetheless, let's move on.
Alan Ritchson mentions a formula that explains the action depicted in Reacher. Let's examine this scenario further.
If I were to break a zip tie (which I wouldn't), I would leverage my arms as a type of lever, as illustrated above. With your fists together serving as the pivot, two forces act on each arm, generating torque around that pivot. The upper segments of your arms, being further from the pivot than the zip ties, can produce the same torque with reduced force.
Focusing on the upper arm in the diagram, let's designate F_T as the maximum force exerted by the zip tie (534 Newtons) and r_T as the length from the pivot to the zip tie (approximately 5 centimeters). If we assume a torque arm for the applied force to be 35 centimeters (to the elbow), we can calculate the force required to break the zip tie. This results in about 76 Newtons (or 17.1 pounds). While this may not seem too challenging, humans typically don't push their arms in this direction, making it a significant exertion.
Section 1.2: Calculating Punch Force
Alan claims that an average professional boxer can deliver a punch with a force of about 776 pounds (or 3452 Newtons). It's essential to clarify that a single number cannot encapsulate the force of an impact like a punch. The interaction between two objects (for instance, Reacher's fist and an assailant's face) is influenced by multiple factors, and the force is a characteristic of that interaction rather than the fist itself.
Consider this example: If Jack delivers a punch with a boxing glove and then punches the same way with a bare fist, assuming both punches initiate with the same speed and mass, they will result in the same change in momentum (calculated as mass times velocity).
However, the distinction lies in the stopping time. A boxing glove being softer will have its impact spread over a longer distance and time. If we plotted the impact force against time, we would see different patterns for each punch.
The area under each curve represents the change in momentum (which remains constant). For the bare fist, the force spikes to a higher level within a shorter time frame to maintain the same area. Thus, while the punches may be similar in some respects, their impacts can yield very different results.
If you're interested in more detailed methods for measuring impact force, check out my recent article on WIRED.com that delves into this subject.
Chapter 2: Analyzing the Set Design
What about the set in the video? The aim seems to be portraying Alan Ritchson as a scientist. However, science isn't solely about lab coats, textbooks, and chalkboards. It's crucial to convey the idea that everyone can be a scientist, not just those in lab attire.
On the table, there are two well-known introductory physics textbooks, although some titles are obscured. I recognize them: Halliday and Resnick (currently in its 12th edition) and Serway’s Physics for Scientists and Engineers (4th edition). The math books are less identifiable, but one simply bears the generic title “MATH.”
Among the props, there’s an abacus manual calculator—an outdated but visually appealing item—and a Newton's cradle, which is more commonly found in office spaces than physics labs.
Lastly, there’s a coffee cup and a notebook, staples in any physicist's workspace. Now, let’s examine the chalkboard, which isn’t perfectly in focus. I’ll offer some insights into what’s visible.
I could analyze this board in detail, but I’ll keep it brief. Here are some key points:
- There’s a mention of circular motion, possibly in relation to modeling a punch.
- Three graphs illustrate acceleration vs. time, velocity vs. time, and position vs. time—standard topics in introductory physics courses.
- An integral for deriving velocity from acceleration is present, followed by the equation d = (1/2) a t², which is frequently used but not entirely accurate.
- The left side includes some kinematic sketches and a figure of a leg's bones, though the calculations remain unclear.
- Notably, the equation F = ma appears, but it should specify F_net, with both F and a treated as vectors.
- There’s a section titled “force of a punch” that seems to calculate force using prior velocity changes, though the mass of the fist and the time interval are unclear.
- A calculation regarding pressure on a femur is also visible.
Section 2.1: Recommendations for Improvement
If Amazon Prime sought my advice on enhancing this science skit, here’s what I would suggest. Having worked on productions like MythBusters and CBS MacGyver, I have some relevant experience.
- Improve the equations on the board by showcasing physics problems directly related to the show—this would add a fun twist. The random graphs could be omitted since they don't contribute significantly to the main focus.
- Ditch the lab coat! Scientists should be depicted as everyday people.
- Consider replacing the props on the table with engaging physics demonstrations. For instance, dropping two eggs from the same height—one on a cushion and the other on a hard surface—could illustrate impact forces.
Overall, this video is enjoyable and serves its purpose well, capturing Alan's enthusiasm. If I were to assign a letter grade, I’d give it a B+.