Scissors, Paper, Rock...
and three ways they relate to handedness. 🤲🏽
As a rightie with the world and its tools designed for me, I never thought about left-handed scissors.
Not until my fiance challenged me to try and use scissors in my left hand. 🤯
The struggle had me shook, and the search for answers cut me into little pieces and scattered my remains across countless browser tabs. The theme for this week jumped from symmetry to mirrors, to alternate universes and perhaps if you read on you’ll catch a glimpse of why. But I ultimately decided against any of those because they opened up a can of worms that my cut up brain couldn’t handle. You can bet that I’ll get back to them in the future but for now, here’s a lot of random information about:
Handedness and scissors, paper, rock…
SCISSORS ✂️
Left and right-handed scissors. What an unexpected doozy. I thought that for sure there would be thousands of videos on the science of scissors. But there isn’t, and I think it’s because the question of how handed scissors work is interdisciplinary. There’s the engineering and physics of scissors, as well as the anatomy of handedness to consider. As far as I could google, no one has married the topics, so I’ll do my best to do that here.
In a mechanical sense, scissors are two levers that use the force of our thumbs and fingers to bring the two cutting blades together. The best dummy internet explanation that I could find is here. The blades moving past each other in opposite directions apply ‘shear stress’ to the material and when the force of the shear stress is greater than the ‘shear strength’ of the material, you get a cut. Sharp blades localise and apply the stress to a finer point that makes it easier (requires less force) to make a cut. This is why sharp scissors cut better.
Because the blades overlap, scissors are symmetrical, just like our hands. A single pair of scissors won’t work in one hand as they do in the other, in fact, they will work in the opposite way.
Righties don’t need a special lefty ball to throw because a ball is symmetrical. A ball will work in the same way in either hand - how well we use it comes down to how well we can develop our motor skills with the ball in each hand.
With asymmetrical scissors, it is our motor skills, plus the mechanics of the scissors in play. As the expert explains above, scissor blades are designed for the mechanics of one hand to bring the blades together. In the other hand, the mechanics are mirrored which forces the blades apart.
Bonus complicated note: this isn’t a law of physics. I actually found that I could use my right-handed scissors to cut through paper using either hand, but I couldn’t use my left hand to cut through plastic even though I could with my right. My guess is that my left hand couldn’t finesse the blades together enough to exert shear stress greater than the shear strength of the plastic. But that’s just a laylady guess. I would love for someone smarter to turn all these internet snippets into one comprehensive explainer. Please, now, thank you.
WATCH: If you don’t care about scissors, you might enjoy this video about handedness in general… Why are some people left-handed?
PAPER 📃
The asymmetry of our hands is an example of chirality, of which there are many examples in the natural world. In my browser travels, I learned that chirality in chemistry is when a molecule or ion cannot be superposed on its mirror image. This is called an enantiomer.
The enantiomer rabbit hole led me to this article in the Smithsonian on artist Matt Shlian’s 2016 exhibition ‘Chirality’. It does a good job of touching on the relevance of enantiomers with recognisable examples but is also a brilliant example of the greatness that can come from the marriage of art and science.
ROCK ☄️
Handedness in life’s molecules, like that of handedness in humans, seems to have a preference. Another article in Smithsonian explores why the molecular building blocks of life display chirality. In amino acids, the preference is a left-handed shape and sugars are right-handed. It’s possible to have amino acids and sugars that prefer the opposite side, but almost all life on earth exhibits the first preference. This begs the question: why tho?
This phenomenon is called ‘homochirality’ and like my foray into scissor handedness, has led to a long list of new questions.
“How and why did life choose only one of two mirror reflections to construct every single creature in her menagerie? Does life require homochirality to get its start, or could life forms exist that use both the earthly building blocks and their alter egos? Did the seeds of homochirality originate in the depths of interstellar space, or did they evolve here on Earth?”
Answers are hopefully on their way with the return of the OSIRIS-REx spacecraft. It’s currently on its way home from the primitive asteroid Bennu where it was on a mission to collect samples. Bennu was chosen partly because it wouldn’t have changed in its 4.5 billion years and its thought that it may contain the molecular precursors to the origin of life or at least help with the homochirality conundrum. We’ll know more when it lands on Sept. 24, 2023.
THEME SONG: Rock Paper Scissors - Jah Sun, The Rising Tide
A literal, relaxing choice.
Til next time, stay curious!
Alegria