Vertically-vibrated Granular Studies

Topic: Granular Materials

Granular materials are interesting because they can show properties of both fluids and solids. The classic example is sand, but it can be any sample of a bunch of (usually small) grains, or particles, that are of course solid. Researchers have used small beads, pepper, salt, peas, rice, and so on. Think of something like an avalanche, where individual small solid objects 'flow' down the incline - here, solid objects collectively show something more like a liquid flowing.

A really interesting phenomenon happens when one vertically vibrates granular materials. When one does this with small bronze beads or sand, there are certain combinations of frequency and amplitude where a variety of patterns appear. These patterns always remind me of interference patterns of liquids. Small piles that also form patterns also appear, called oscillons.

In order to oscillate granular samples, one can purchase a mechanical oscillator from a variety of supply companies, such as PASCO, Arbor, and others. Many high schools may have some version of this to form mechanical waves on strings or to vibrate Chladni plates. These go for under $200. To drive the oscillator requires function generators; there is a simple sine wave generator from PASCO that goes for $270, or a more robust function generator that is more expensive at around $700. Some people have used speakers to create vibrations. Granular samples can be placed in petri dishes that are attached to the oscillator.

The vibrated granular experiments can be done easily in a school lab or in a student's basement or bedroom! Data collection is most easily done with video techniques. Be sure to have a ruler or some size standard to measure distances, radii, heights of piles (with a camera with a side view of the material).

Research Ideas for vibrated granular materials:

• Classic crating oscillons and multiple patterns by vertically vibrating sand, small beads, bronze powder, or any other granular material. You can vary size of grains, size of container being vibrated, frequency and amplitude combinations, depth of granular materials, mixtures of different sized grains. (an example)
• Patterns in granular materials at high frequencies (an example)
• Patterns that form when experiment is inside a vacuum, or as a function of air pressure if one has a bell jar and vacuum pump
• Behavior of vertically vibrated piles of granulars; any pattern formation and/or avalanching
• Observations and search for patterns/pile formation/avalanching when granular material is falling onto a vertically vibrating surface (compared to a stationary surface).
• Patterns of vertically vibrating granular materials when the experimental setup is rotating
• Patterns of vertically vibrating granular materials when the experimental setup is on a pendulum, or moving (accelerating) horizontally.
• Pattern formation as a function of moisture/dampening of the granular material (such as wet sand; different levels of wetness)
• If multi-sized beads/grains, is there any stratification or segregation of beads when vertically oscillated 
• Mixing properties of the layers of grains when vibrated; if you have different colored sand, for example, make layers by color, and then find out how the mixing takes place among layers. (an example)
• Search for any horizontal movement/drifting/mixing while vertically vibrating. (an example)
• Effect of barriers, compartments, or obstacles in the container on the pattern formation of the vibrated granular materials
• What happens if a granular sample is vibrated back and forth horizontally?