Dragging a toy on a piece of string is a time-honored way to entertain a cat. The problem is, it may be less fun for you than it is for the cat.
Can the process be automated? After rigorous, exhaustive testing, I have determined that a compound pendulum is the simplest way to do it. Compound-pendulum projects have been published previously in both Make: Volume 22 and Volume 50, but they used motor-driven levers and created their output with LEDs. My version just needs two weights, a piece of string, and an output device commonly known as a “mousie” (Figure A).
The length of a pendulum determines how quickly it oscillates. Consequently, when you have two weights that are linked together but are hanging at different heights, the movement of the higher weight interferes with the movement of the lower weight, and the result is a series of chaotic movements that cats find interesting.
To keep the pendulum swinging for as long a time as possible, the weights should be as heavy as possible. However, this is a potential hazard: If you build this project, be sure to suspend the weights securely, so that they don’t fall on top of your cat. I cannot take responsibility for feline injuries caused by substandard pendulum construction.
CAUTION: Dangling cords can also pose a strangulation threat to toddlers, so please choose a safe location to mount this project that will not be accessible to small children.