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Density-potato-float (Kenneth Howard)


Potato Float


by Kenneth D. Howard

Principles Illustrated




           A substance has  characteristic properties, such as density, which are independent of the amount of the sample.

Questioning Script

Prior knowledge & experience:

        Students know when an object is heavy it will sink and when it is light it will float when placed 

        in a liquid.  They are not really familiar with the physical property of density.  


Root question:

        Which has the highest density the water or the potato? (After placing a piece of potato in the first glass)

        Which has the highest density the water or the potato? (After placing the piece of potato in

        the second glass.)



Target response:

Students should respond the water is more dense and the potato is less dense in the first glass.

Students should respond the potato is more dense and the water is less dense in the second glass.

Common Misconceptions:

        When presented with a density gradient of different liquids.  Many students accidentally 

        think since a liquid is at the top of the gradient it has the highest density and when it is at the 

        bottom it has the lowest density.  This is the opposite of what is true. With this demonstration 

        if the students are  asked what has the highest density sometimes respond to whatever is

         highest the potato or the water if the potato is resting at the bottom.  If the students are asked 

        which is heavier they  respond to whatever is the at the bottom but mass and weight are not 

        physical properties of matter.


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