"Science: Why Shoelace Knot Failure"

Question

by Nsikan Akpan

Right off the bat, they found shoelaces didn’t untie when a person just swung their foot nor when they only stamped the ground. The combination of the two activities, which define walking and running, appeared responsible.

The team acquired a high-speed camera and pointed it at Gregg’s shoes as she ran on a treadmill. Gregg had tied her laces with one of two knots: square (strong) knot or a granary (weak) knot. Here’s how O’Reilly described the difference between the two:

You tie the laces first. That’s where you loop the strands together, one around the other. Next, you form the “bunny” knots. If you loop the bunny knots together the same direction that you tied the first knot together, that’s a weak knot. But if you do the opposite. Instead of putting one over the other, you switch the order, then you get the strong knot.

What the team noticed in the videos was nothing happened for a long time, and then — all of the sudden — the laces came untied, typically over the course of two strides. It didn’t matter if Gregg had used a strong knot or a weak knot. To break down the physics of the phenomena, the researchers attached a small device to the free end of the laces that measured acceleration, and then Gregg went for a walk or a jog. This acceleration creates inertia, which is the tendency for an object to keep moving once it is in motion.

Use the passage to answer the question.

How do O’Reilly and his graduate students test their theory that the physics of running and walking cause shoelace knots to come undone? Select the two correct answers.

(1 point)
Responses

They tied a variety of knots with various strengths.
They tied a variety of knots with various strengths.

They attached devices to the laces to measure acceleration.
They attached devices to the laces to measure acceleration.

They swung their feet.
They swung their feet.

They stamped their feet on the ground.
They stamped their feet on the ground.

They used a high-speed camera to monitor movement on a treadmill.

Answer 1

The two correct answers are:

1. They attached devices to the laces to measure acceleration.
2. They used a high-speed camera to monitor movement on a treadmill.