Density & Buoyancy-Ice cubes in water and rubbing alcohol (Mahya Babaie)

Author

Mahya Babaie

Principle(s) Illustrated

1. Density

2. Buoyancy

Standards

8.a. Students know density is mass per unit volume.

8.b. Students know how to calculate the density of substances (regular and irregular

solids and liquids) from measurements of mass and volume.

8.c. Students know the buoyant force on an object in a fluid is an upward force equal

to the weight of the fluid the object has displaced.

8.d. Students know how to predict whether an object will float or sink.

Questioning Script

Prior knowledge & experience:

Ice cube floats when placed in liquid water.

Root question:

What will happen to the ice cubes if they're placed in each solution? Sink or Float?

Target response:

Materials that are less dense than water (or have a density lower than 1.00 g/cm3) will float in water, while materials that are more dense than water (or have a density greater than 1.00 g/cm3) will sink. The same is true of any liquid, such as ethyl alcohol with a density of 0.79 g/cm3. Materials less dense than ethyl alcohol will float in it, while materials more dense will sink. Therefore as observed in this demonstration, ice with a density of 0.92 g/cm3 will float in water but will sink in ethyl alcohol.

Common Misconceptions:

Ice cube would float in both solutions.

Photographs and Movies