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Comment by ianferrel | Hacker News Reader

>You don't have to apply force in any different direction if you put scissors with symmetric handles in the wrong hand.

Yes! You do!

So scissors hinge on a pivot point, and they hinge in two dimensions. They mostly move in the dimension that they cut in, but they also move a little in the perpendicular dimension. And in order to bring the cutting edges closer, you move the handle ends farther away. If you're using the correct-handed scissors, doing so is easy and natural because your hand grip curls one way easily. If you then switch the same scissors to the other hand, it's hard and uncomfortable because your other hand is a mirror image and your natural hand grip curls to bring the handles closer and the cutting edges farther away.

The fact that you keep mentioning that this violates some law of physics is bonkers.

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It’s because people aren’t aware the 2nd dimension, the looseness of the connection between the planes of the blades, where the screw isn’t (and can never be) perfectly tight yet still allows the blades to slide. It’s hard to get the idea across in text. Your second comment helped a lot.

Your thumb and fingers of both hands are equally capable of producing both separating and joining force while closing. You learned to do it one way, by pushing out with your thumb and pulling in with your other fingers, so that way feels better to you, but that's a property of you not a property of scissors.

It's so weird you are choosing this hill to die on. And you are completely wrong; 7-year-old left-handed me had the empirical experience to know this.

>Your thumb and fingers of both hands are equally capable of producing both separating and joining force while closing.

What makes you so sure? The ergonomics of the thumb, fingers, and hand are not symmetric. The left-handed people who struggled with right-handed scissors as kids suggest otherwise.

It's got nothing to do with hand capability, you've misunderstood. For an ambidextrous person, using right-handed scissors in their right hand will work properly, using right-handed scissors in their left hand will work poorly. And vice versa for left-handed scissors.

When holding scissors, the bottom blade is held fairly steady. The top blade tends to get pushed away from the rest of the hand by the action of the thumb. If the top blade is on the far side of the scissors (away from the hand), the far blade edge will get pushed towards the near blade edge when the thumb handle is pushed away (because the blade is on the other side of the hinge from the handle). If the top blade is on the near side of the scissors (the hand side), by pushing the thumb handle away from you, you are separating the two blades rather than pushing them together.

So on right handed scissors, with the thumb handle facing up, the thumb blade is on the left side of the hinge. That way the natural "push away" force from the thumb will keep the blades close together when held in the right hand. On left handed scissors, the thumb blade is on the right side of the hinge, for the correct push-together force when held in the left hand.

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