Why do Pendulum Clocks Stop During An Earthquake?

Most of you who have had Pendulum clocks for quite some while might have noticed that they stop whenever there is an earthquake. And this makes many wonder why this phenomenon occurs. So we decided to answer that very question in this article.

Basically, it happens because pendulum clocks are dependent on their pendulums for timekeeping. Due to the Earthquake waves, the pendulum gets disturbed and so the timekeeping gets messed up.

We’ll talk in detail about this question in this article and we’ve provided a table of content so you can quickly skim through it.

Before we address the question, it would be quite important for us to learn about How Pendulum Clocks Work and Which Parts Perform Which Function? To do so in detail you can check out this article. In this article, we’ll go briefly over these topics to encourage a better understanding.

What Are Pendulum Clocks Made Of?

Why Do Pendulum Clocks Stop During An Earthquake?, Question Mark

Pendulum clocks are basically made out of these essential parts:

  • A Power Source
  • A Gear Train
  • An Escapement
  • A Pendulum
  • An Indicator

Now let’s talk briefly about these parts and how they work together. Firstly, A pendulum clock is powered by a single power source, this power is generated by a pendulum attached with a weight that generates potential energy to drive the clock system. Secondly, there are two types of gears in a pendulum clock, Timekeeping Gears, and Power Gears. Timekeeping gears are used to well keep time. They are made so that if second-hand moves, the minute and the hour hand are also moved but at a much slower rate. For, example if second-hand moves, the minute hand is moved at 1/60th of its speed and vice versa. Power gears, on the other hand, provide a very different function, they are used to convert the potential energy so that it can be used to power the clock mechanism.

Another important part of the pendulum clock is the escapement, escapement works alongside with the pendulum to keep time. It is kept in place because of a simple function, it lets only one position escape on the dial in a time of a second. As the pendulum swings, it locks and unlocks the part of the mechanism which is driven by the weight. Lastly, an indicator or a dial is used to display the time

How Does A Pendulum Clock Work?

Why Do Pendulum Clocks Stop During An Earthquake?, Pendulum Clock

The weight is used to store potential energy which is then transferred to the clock mechanism. The clock requires winding for the potential energy to be stored. The power gears are used to convert the potential energy and use it to function the clock, the heavier the weight the more energy will be stored and the clock will function for more time without requiring it to be wound.  Timekeeping gears are used to drive the different hands of the clock for showing proper time. Finally, the pendulum and escapement are used for regulation and proper syncing of time with the rest of the system.

Due to the energy requirement being already fulfilled by the potential energy stored in the weights, this type of clock system does not require electrical energy to be powered, but there are some drawbacks. The clocks, once wound, might keep on running for several days but after some specific time, they will require to be wound once more which is a hassle in itself. Furthermore, they are not nearly as accurate as their electrical counterparts, mainly due to two reasons. Firstly, due to the gravitational field, the weight varies from place to place and the other reason is the expansion or contraction of the metal used to make the pendulum.

Why Do Pendulum Clocks Stop During An Earthquake?

Why Do Pendulum Clocks Stop During An Earthquake?, Earthquake

Now that we have a better understanding of how the clock works, let’s get to the main part of this article and see how an earthquake affects a pendulum clock. Pendulum clocks are not always stopped during an earthquake but it’s pretty common. The reason being the fact that pendulum clocks are completely powered by the pendulum. When the earthquake waves hit, they disturb the pendulum and so the clock eventually stops.

Let’s talk in detail about it. During an Earthquake, two types of waves are transmitted 1. Body Waves 2. Surface Waves. Body waves comprise of primary waves and secondary waves. The body waves aren’t very destructive, it’s the secondary waves that do all the destruction. Seismic waves are longitudinal in nature, this means that they push and pull. This pushing and pulling messes up the pendulum of the clock which results in the clock stopping. This can do two things, either it can make the pendulum swing further way or it can make the pendulum slow down. Both of these things are equally damaging as they mess up the rhythm. So if the pendulum can’t trigger the escapement the clock stops.


To conclude, pendulum clocks can be messed up by an earthquake due to its mechanical nature. The longitudinal seismic waves mess up the pendulum’s rhythm which eventually stops the clock.

AK Iqbal

A University of London’ student with a passion for writing. Clocks have always intrigued me and the importance that they have in our lives is way beyond phenomenal. So, on this site, I write everything about clocks, everything from answering any clock-related queries that you might have along with recommending some of my favorite clocks accordingly. Moreover, I will also be conducting some researches on clock related topics and sharing the things that I learn. So stay tuned to ohmyclock for all the fun clocks related content

Recent Content