Displacement of Fluids

Thomas J. Billups              Delano Elementary
                               3937 W. Wilcox
                               Chicago IL 60624
                               (312) 534-6620

Objectives:

This activity was designed for grades 4th thru 8th.  Students will acquire a 
working definition of the word "displacement".  Students will also understand 
that the volume (size) of an object placed in water affects the amount of water 
that is displaced. 

Materials Needed:

Students will be in groups of 3-4 individuals.  Each group should have the 
following items:

2 liter bottles (tops cut away)                         3ea.
300 gram weight                                         1ea.
800 gram weight                                         1ea.
1200 gram weight                                        1ea.
1 liter graduated cylinder                              1ea.
balancing scale                                         1ea.
styrofoam cup                                           1ea.
1/4" plastic tubing (ink pen shell)                     1ea.
2 objects same weight (500-1200grams) but different volumes
2 objects same volume but different weights (1 plastic block & 1 styrofoam 
   block) 

The 2 liter bottles are converted into overflow containers by taking a Phillips 
screw driver and heating the tip and using the tip to melt a hole into the 
container.  The hole should be 3cm - 4cm from the top of the container.  Next, 
place the 1/4" tubing into the hole, making sure to get a tight fit.  The tubing 
allows for all the water from the container to flow into the graduated cylinder. 
* Note the water level should be at the point that water flows thru the tubing 
then stops.  This level should be reached before performing exercises 2 thru 4. 
                                                                     
Strategy:

Students will be introduced to the concept of displacement by observing the 
following exercise.  Take two 2 liter containers filled 3/4 of the way with 
water.  A 200 gram weight is placed in one of the containers of water and a 
1,000 gram weight placed into the other container.  Students should notice that 
the water levels have increased.  Students should also notice that the container 
with the 1,000 gram weight has the higher water level.  Students are then 
informed that, in each case, the change in water levels is a measure of displacement.  
Displacement is the amount of change in fluid volume from the initial point 
(beginning water level) to an ending point.  Students are then asked to construct 
a definition of the word displacement based on their observations.  Students are 
then asked to theorize as to what led to the different levels of displacement.  
Most students tend to theorize that the heavier objects' weight leads to a higher 
water level.  Students are now ready to perform the following experiments to 
test their theories.  Have students form  groups of 3 or 4 individuals, so that 
each group will conduct the following experiments.  

    Experiment 1: 
    Place the various weights (300, 800, and 1200 grams) into different identical 
containers and notice the change in water levels of the three containers.  Once 
again, students should notice that the greater the weight in the container the 
higher the level of displacement.  This observation may lead to the conclusion 
that the weight of an object affects the amount of water that a object 
displaces. 

    Experiment 2:
    On a balance scale have students weigh the two objects of the same 
weight but different sizes.  Next, place each object into an overflow 
container and measure the amount of water displaced.  Any object that floats 
should be held below the water level, until the (displaced) water empties into the 
graduated cylinder.  Students should notice that the object with more volume 
(greater size) displaces more water.  Students conclude that it is an objects' 
size that determines the amount of water displaced.  To prove the findings of 
experiment 2, perform experiment 3. 

    Experiment 3:
    Place the two objects of similar volumes and different weights into the 
overflow containers.  Students should notice that both objects displace similar 
amounts of water, which would substantiate the findings of experiment 2. 

    Experiment 4: 
    Now place the 300 gram weight into the over flow cylinder and record the 
amount of water displaced.  Next, hold an inverted styrofoam cup submerged under 
water and  record the amount of water displaced.  Once again, students should
notice that the cup displaces more water than its weight, further illustrating 
that it is the volume of an object that determines the amount of water that the 
object displaces.  

Performance Assessment:

Students will receive a maximum of 20 points for each experiment completed.  A 
two question essay (20 points) will also be administered.  A maximum of 100 points 
is possible. 
                           100-90  = A
                            89-80  = B
                            79-70  = C
                            69-50  = D
                            49-20  = F
                            19-0   = 0
  
References:
  
  "Archimedes' Principle", Encyclopedia Britannica, 1991.