Why Cheerios Don't Sink 

CHRISTINE S. SMITH             ENGLEWOOD HIGH SCHOOL
                               6201 S. STEWART AVENUE
                               CHICAGO, IL 60621
                               1-312-723-1710

OBJECTIVES:
     Students will participate in the demonstration in order to discover 
Archimedes' Principle and how it relates to density, and gain practice in using 
the scientific method. 

MATERIALS:
     Large beaker (5000 mL), 200g weight, styrofoam bowl, water, spring scale  or 
pan balance with hook, overflow cans, graduate cylinder, string, wax pencil 

STRATEGIES:  
 1. Add 3000 mL of water to the beaker; place the 200 g weight at the bottom of 
    the beaker and float the styrofoam "boat" on top .  Mark the level of water. 
 2. Ask the question, "What will happen to the level of the water if I take the 
    weight out of the water and place it in the boat?". 
 3. Ask students to explain their predictions. Take the weight out and place it in 
    the boat. 
 4. Ask students how they could verify their hypothesis. Make balances, overflow 
    cans, and graduates available. 
 5. Students will weigh the 200 g object outside of the water and then weigh it 
    while it suspended in the water. Using an overflow can they will collect the 
    water that the object displaced and measure its volume and mass.  Measure and 
    calculate the volume of the 200 g object. 
 6. From step 5 students will determine : 
    a: Object's weight loss in water = Displaced water's weight 
    b: Object's volume = Displaced water's volume
    c: Water's mass = Water's volume
 7. Students will repeat step 5 for the object and boat while it floats.
 8. From step 7 students will determine:
    a: Object's weight loss on water = Displaced water's weight
    b: Object appears weightless
    c: Object's volume > Displaced water's volume
 9. From steps 5 and 7 students will state:
    a: Archimedes' Principle: Objects will lose weight in water equal to the 
       weight of water they displace.
    b: Density = Mass / Volume
       Water: Mass = Volume                Density of water = 1 g/mL
       Floating Objects: Mass < Volume     Density < 1 g/mL                 
       Sinking Objects: Mass > Volume      Density > 1 g/mL
10. Give students a ball of clay and have them drop it in a beaker of water; ask 
    them to make the object float. 
11. Have students determine the density of Cheerios.