Hanging Oil Drop

It gets stuck half way

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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.

Nature - 

Demonstration

Materials - 

Measuring cylinder, Colourless Methylated Spirits, Water, Coloured Oil, Long Pipette

Method - 

· 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.

· 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.

· 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 -

A dark coloured vegetable oil works well as it is easier to see for the students.