Density-potato-float (Kenneth Howard)

Title

Potato Float

Author(s)

by Kenneth D. Howard

Principles Illustrated

Solubility

Density

Standards

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.

Photographs and Movies

References

http://www.mcrel.org/whelmers/index.asp