Hanging Oil Drop

It gets stuck half way.

 

 

 

Category - Solids, Liquids & Gases

Key Idea - Density

 

Purpose - A magic trick that illustrates the effect of variations in density.  It is also interesting to note the formation of a perfectly spherical oil drop.

An oil drop apparently suspended in mid fall. 
Nature -  Demonstration
Materials -  Measuring cylinder, Methylated Spirits, Water, Coloured Oil, Long Pipette
Method - 
  1. Before class half fill the measuring cylinder with water, then carefully float the methylated spirits on top of the water. It should be difficult to see the separation.
  2. In class drop a couple of drops of coloured oil into the measuring cylinder.  They should float down to the half way point then stop, suspended apparently in the centre of the liquid.
  3. You can carefully remove the oil drops with a long pipette and reuse the floated methylated spirits.
Safety - Nil
Explanation - The coloured oil is more dense than methylated spirits, so it sinks in this.  It is less dense that water, however, so when it reaches the water / methylated spirits boundary, the oil stops sinking. This is an excellent extension demo for students studying density.
Notes - The coloured "oil" used in this demo is actually made from *********