Buoyancy: What will float and what will sink

Suzzanne' O'Quinn              Phillips Alternative High School
                               700 E. Oakwood Blvd.
                               Chicago IL 60653
                               (773) 624-4493

Objectives:

This lesson is aimed at the intermediate grade levels (4-6).  The students will 
be able to write and verbally explain why a particular object/item will sink or 
float.  They will also be able to illustrate and/or demonstrate this process.  
This assignment will either introduce graphing or enhance a students graphing 
skills, as well as their critical thinking skills. 

Materials Needed:

1 Large Clear Container - filled with water
2 Balloons of the same color (one filled with water and one filled with air
                              but close to the same size)
1 Regular Coke
1 Diet Coke
2 Empty 16oz clear water bottles.  (one filled with a much heavier substance
                                   than the other.  Ex: Flour and Salt; air
                                   and water; Salt and sugar)
Fruit:  two of each of the following: pear, apple, orange, nectarine, banana,
                                      lime, potato, plum, tomato, lemon, etc.
Enough copies of a graphing chart of which fruit will float and which will sink
1 Roll of aluminum foil
100 pennies
1 empty but clear dish washing detergent bottle with cap
2 glass droplets

Strategy:

I have a container of water and two balloons of the same color.  (One is filled
with water and the other with air.  DO NOT INFORM THE STUDENTS OF THE BALLOONS 
CONTENT).  At this time, I will show the students the two balloons and ask them
as I place each one in the water what do they think will happen?  (Placing the
two balloons in the container, I now wait and listen to the students 
observation).  POSSIBLE ANSWERS:  One sunk because of its weight, one balloon 
was bigger than the other, one is filled with water and one with air.
  
Then, I will continue with the two pop cans.  I will show the class, two 12oz 
pops, one being diet and the other regular.  I will ask them, what do they think 
will happen as I place both cans into the container of water?  (At this time I'm 
listening to the students responses.)  Then I place the two cans of pop into the 
container of water, and one floats and the other doesn't.  I ask why?  (Listen 
to their responses.)  Then, explain why what happened, happened.  Diet coke 
contains nutra-sweet and regular coke contains corn syrup.  Corn syrup is more 
dense than the nutra-sweet that is in the diet coke; therefore, the diet coke 
was able to float more than the regular coke.  Cheap pop may float, not enough 
corn syrup. 

Next, I will hold up two 16oz clear water bottles filled with a white content 
(one with baking soda and the other salt.)  Once again, I will ask the students 
what they think will happen when I place them in the container of water?  
POSSIBLE ANSWERS: one will sink, the other will float.  They both will sink or 
float.  Well, after placing both bottles in the water, the students received a 
surprise.  They both sunk!  Why?  I listen to the observations and let them 
discuss what they think happened.  (That is why under the materials I listed 
several contents.  Water and air would have been a good example because one 
would have floated and the other would not have.  However, I wanted the kids to 
see something different.)

Moving right a long, I introduce the class to the different kinds of fruit I 
have available.  I ask that they all come up with their chart and pencil to make 
a prediction on what fruit will sink and what fruit will float.  Then, have them 
try each fruit in the water and see what happens.  This way the children will 
have a visual graph of what floats and what sinks.  (The teacher must do the 
experiment himself/herself to find out these results.  Smile!  Have fun.)  
Afterwards, the students are free to enjoy a piece of fruit.  Now, the floor is 
open for discussion as to what floated and what didn't and why. 
 
All the students will come back up and make a boat or a floating object, one 
out of foil and one out of Play-Doh.  Then, they will place their floating 
device in the container of water to make sure it floats.  If it floats, they 
will see how many pennies it can hold before sinking.  They will write down 
their results and sit down and as a group they can talk about their finding.

Finally, I will demonstrate buoyancy using the clear dish detergent bottle and 
the two glass droplets.  Filling the bottle with water and filling one droplet 
with water and the other half filled with water.  Then dropping both droplets 
in the bottle, closing it tight.  One droplet will sink to the bottom, while 
the other will float to the top.  Place your hands just below the neck and 
squeeze with you thumb and observe what happens.  Then repeat the process using 
your three fingers. 
        
Performance Assessment:

I would expect each student to participate in all exercises.  They should all 
have an idea about why something happened.  I would expect that all the 
students should have a clear understanding of buoyancy, considering the various 
experiences.  Assessing the students should not be stressful.  They should be 
able to identify this concept when they come across it again.