# 1K10.30 Walking the Spool

## Concepts

Torque, rotational dynamics

## Overview

A ribbon is attached and wrapped around the hub of the spool. Imagine a line along the ribbon that intersects the contact point between the spool and the floor as the ribbon is held at a certain angle. When the ribbon is held and pulled below this line, the spool will move toward the direction of the applied force, i.e. forward direction. When the ribbon is pulled above this line, the spool will move in the opposite direction, i.e. backward direction. However, the spool will remain stationary when the ribbon is pulled along this line since there is no torque at the contact point. By holding the ribbon at this angle while you walk, the spool will slide on the floor without rotating so you can "walk the spool."

## Details

### Equipment

• [1] Spool with ribbon wrapped around it

### Script

1. Hold the ribbon such that it is parallel to the ground and pull it. Notice the spool will move toward the direction of the applied force.
2. Hold the ribbon at an angle perpendicular to the ground and pull it. Notice the spool will move in the opposite direction.
3. Imagine a line along the ribbon that intersects the contact point between the spool and the floor. Pull the ribbon along this line and notice the spool remains stationary.
4. Hold this angle while you walk.

• PIRA 1K10.30

#### Disclaimer

• Don't attempt this at home!

• 2017

#### Related demos

If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.

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