Over the course of history, many people have attempted to build a perpetual motion machine, a machine which would continue working forever without requiring the input of any energy. It is impossible to do so in the world we live in, since friction and air resistance always result in energy loss and effectively slow down any machine.

However, in the lobby of the Physics Department in the University of Otago lies a clock that has been running since 1864 without needing to be wound up. It has no batteries or solar panels: it just uses atmospheric changes to wind itself up.

Inside the base of the clock, there is a one cubic foot airtight box, and the air inside expands and contracts based on changes in atmospheric pressure and temperature. This pushes against a diaphragm, which creates enough force to push up a one-pound weight by one inch, which is then used to wind up the clock.

A diagram of a different clock with a similar mechanism can be found here.

Interestingly enough, the Beverly Clock is supposedly the second longest-running experiment in physics, having been continuously running since 1864. The longest-running experiment, according to the University of Otago, is the Oxford Electric Bell, which has been running since 1840.

Sample Problems

1. Look at the weather forecast for San Francisco for the next ten days. Would the Beverly Clock fail on any of these days? In other words, are there any days where the difference between the high and low temperatures is less than 6 degrees Fahrenheit?

2. If you grew up in a city or town other than San Francisco, look at the weather forecast for that town for the next ten days? Would the Beverly Clock fail on any of these days?

3. Are there any cities in the world where the temperature doesn't very by at least 6 degrees Fahrenheit on most days? Try to find one using online weather reports. If that doesn't work, see if you can research locations in the world that have the most consistent temperatures.