Bathtub Physics  - Density, Buoyancy and Flotation

Russell, Renee                      South Shore High School
8431 S. State                       (312) 933-8180
Chicago, Illinois, 60619
(312) 783-3569  (312) 799-1004

Objectives:

Understand Archimedes' Principle, flotation and the reaction of 
bouyant forces.  Explain the relationship between density and 
flotation.

Apparatus needed:

triple-beam balance           800ml beaker
hooked mass 50g               water
spring scale                  bathtub (large container
string                        or pool small)
500-ml graduated cylinder     gallon jug
                  salt solutions: Use Epson Salt
                  1. sea water 3.5g of salt per 100cm3
                  2. Great Salt Lake 20g of salt per 100cm3
                  3. Dead Sea 25g of salt per 100cm3

Recommended Strategy:

1. Record the weight of an hooked mass with a spring scale.  Fill a 
graduated cylinder half-full of water and record the level of water. 
Hang the mass from the spring scale and lower the object until it is 
submerged in the water in the graduated cylinder.  Record the weight of 
the object in the water and the amount of water displaced. 

2. Use a bathtub to find a student's volume.  Fill the tub half-full 
and mark the level.  Submerge a student and mark the level of the 
water.  Once the student is out of the tub, use a measuring device- 
large graduated cylinder, gallon jug - to fill the tub to the higher 
mark.  The amount of water needed to do this will be equal to the 
students volume. 

3. Place an uncooked egg in a 800cm3 beaker half filled with water. 
Next place the uncooked egg in each of the containers of salt 
solutions one at a time.  Make careful observations of what happens in 
each solution and record your data. 

References
Floating - A Key To Survival  Science and Children October 1980 33-35.
Conceptual Physics Paul Hewitt