This is an educational demonstration that simulates how a mass spectrometer works. A mass spectrometer is an analytical tool that can separate atoms and molecules by mass and identify them (and how much of them are in the sample).

Watch an YouTube video of it in action:

https://www.youtube.com/watch?v=Igb48C22eZs

To make this you will need 3 mm and 6 mm MDF boards, a laser cutter, 2 15 mm neodymium magnets and several steel spheres of different sizes.

There is one file for each MDF thickness. The red circle is the magnet position, it should not be cut, just marked lightly on the MDF. Place the side with the mark facing down.

Take the base rectangle and glue the feet in the corners. Glue the magnets in the circle. Prepare the ramp by gluing the sides to the central, thicker piece. Screw the ramp using the holes in the base as a guide. Glue the side pieces to the base.

During class, let each of the spheres fall down the ramp and watch where it hits. Heavier spheres will be less affected by the magnets than light ones.

In the mass spec experiment with atoms, the atoms are injected in a vacuum chamber and ionized, before being separated by the magnetic field. A detector counts how many atoms of each mass are present. That is how we know the percent amount of each isotope of an element.