Demo 1: The Mechanical Clock

Physics Concepts

1. Conservation of Energy
2. Simple Harmonic Oscillators

Required Materials

Material	Amount	Notes
Metal Ruler	1	Recommended 12-15 inches
Vice or Custom Stand	1	Instructions for a custom stand can be found in the instructions for Demo 2. If you plan to run both Demo 1 and 2, it is recommended to build the custom stand.

Construction

1. Place the ruler into the vice (or stand) such that ~2 inches are below the tip of the vice and secure it tightly

Running the Demo

1. Place your vice/stand and ruler combination at the front of the classroom such that all students can see it and so that the ruler is upright
   1. I recommend orienting the apparatus such that the thin edge of the ruler is facing the students
   2. If you are using the same setup from Demo 2, ensure that you have the batteries disconnected so that the electronics do not interfere with the current demonstration
2. Pull back the ruler and let it swing back and forth until it returns to rest
   1. You can also time this process with a stopwatch on your phone to get an idea for how long the ruler takes to return to rest after setting it in motion

Discussion Points

1. Ensure the students understand conservation of energy and ask what they think will happen when you pull back the ruler and let it swing for a while
   1. If they come to the conclusion that it will eventually stop, ask them why they think this is and what might cause it (i.e. the system loses energy due to processes like air resistance)
   2. Discuss how this relates to timepieces via the mechanical watch as the act of pulling back the ruler is like winding the mainspring and it losing energy is like the mainspring becoming unwound
2. Discuss the periodicity of the ruler swinging back and forth
   1. You can make note of how the period changes as the ruler loses energy
      1. For watches that have imperfections, thus making them lose energy non-linearly, this could mean the period of them ticking is off by a bit as it loses energy