Any gift wrapping enthusiast knows that grabbing a pair of scissors to curl a few colorful strands of ribbon is a quick and easy way to put the final touch on a hand-wrapped present. But now, the BBC reports that scientists have finished the first complete physical study on ribbon curling, published in the journal PNAS, and discovered the principles at play when we use scissors to curl a ribbon.
To study the physics of ribbon curling, researchers draped a thin ribbon across a blade, wrapping one end around a cylinder and attaching the other to a weight. Researchers experimented with different weights, blades, and wrapping speeds, observing the ways the ribbon curled when they wound the cylinder faster or slower, used a sharper or duller blade, or used heavier or lighter weights.
They found that sharper blades and slower movements produced tighter curls. As the ribbon was pulled across the blade, its outermost side would begin to stretch and deform, while the side touching the blade would remain the same. This uneven stretching, scientists explain, is what caused the ribbon to curl. Sharper blades, the scientists found, increased the stretch in the ribbon, causing curls to form.
"The first part that's going to start to yield is the outermost part of the ribbon, because that's the point where the stress is going to be highest,” researcher Anne Juel told the BBC. “And then as you apply larger loads, the yield is going to infiltrate deeper and deeper inside the ribbon."
One of the most fascinating discoveries, however, was that increased tension on the ribbon only increased curling to a point. Once the stretching in the ribbon passed the halfway point within the ribbon and began to affect the side of the ribbon closest to the blade, curling effects were reduced. As Juel explained to the BBC: “The tightest curl will be obtained when you manage to apply a load that will bring yield to exactly half the thickness of the ribbon.”
While these findings may not have much of an impact on how you curl ribbons—if you’re a gift-wrapping expert, you probably already knew sharper scissors were better than dull ones for getting the perfect curls—it’s fascinating to learn the physics at play when we perform a task as simple as curling some ribbons for a present.