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What Determines whether an object floats or
sinks?
Pat and Sam are discussing why some objects float while others sink. Pat thinks that heavy
objects sink and light objects float. Sam believes the size of the object is what matters, meaning
if you have two spherical objects, the bigger one will sink and the smaller one will float. Your
task is to determine which, if either, student is correct.

Part 1: Test Pat’s Hypothesis
1. Go to http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=362

   At this site you are able to measure mass, volume (using water displacement), and use a
tank filled with liquid to test whether each item floats sinks.
   When you mouse over the objects, a number will appear. We will use these numbers to
identify each object.
   Be sure the density of the beaker of liquid is set to 1g/ml.

2. Left Column - Discuss your initial thoughts. Here are some topics to consider:
 What do you think about Pat’s hypothesis?
 What do you think about Sam’s hypothesis?
 What do you think determines whether an object will float?
 Look at the objects on the shelves in the simulation. Which of the objects on the
shelf do you think will float? Which do you think will sink? Explain your
reasoning.

3. Create a data table in the right column of your notebook. Your table will need three columns;
Object #, Mass (g), and Float or Sink? Measure the mass of objects #1- #12, then rank them
from lowest to highest mass in the data table.

Sample Table
Object #                         Mass (g)                    Float or Sink?

4. Do your results indicate a clear relationship between mass alone and whether an object floats
or sinks? Explain your reasoning. (Left Column)

Part 2: Test Sam’s Hypothesis.
5. Create a data table as shown below. Measure the volume of objects #1-#12, then rank them
from smallest volume to largest.
Sample Table
Object #                  Volume (ml)                 Float or Sink?
6. Do your results indicate a clear relationship between size (volume) and whether an object
floats or sinks? Explain your reasoning. (Left Column)

Part 3: Another option – Density
7. Create a data table as shown below. Calculate the density for each object, then rank them
from smallest density to largest.

Sample Table
Object #                      Density (g/ml)                Float or Sink?

8. Do you see a relationship between density and whether an object floats or sinks? Explain

9. Left Column - Summarize your learning to this point: Here is a topic to consider:
 Which student, if either, Sam or Pat was correct? Explain your reasoning.

Part 4: Can you make a sinking object float without changing the object?
10. Place one of the objects that sank back in the beaker. Slowly change the density of the
liquid until the object floats. Once you get the object to float, what happens if you decrease
the density? Try to make objects that were floating, sink, and objects that sank, float. Be
sure to create a data table to record your results.

Sample Table
Object #              Object Density         Liquid Density at which    Liquid density at which
(g/ms)                object changes from        object changes from
floating to sinking    sinking to floating (g/ml)
(g0/ml)

11. Summarize your learning for today’s activity. Here are some topics to consider:
 What did you do?
 What did you expect?
 What did you learn?
 Considering your data from Part 4, how many pieces of information do you need in order
to determine whether an object will float or sink? Explain your reasoning.
Assessment:
Imagine the Rocky Mountains of Colorado. What do you see? Among the many sub-ranges that
make up the Colorado Rockies, there are fifty-four summits that reach above 14,000 feet in
elevation. No where else in the Rocky Mountain chain, which stretches from Texas to Canada,
do the summits reach these heights.

It is interesting that Colorado contains so many peaks over 14,000 feet in elevation yet not a
single peak higher than 14,500 feet. Use the link below to help you explain why the peaks do
not rise above 14,500 feet.

http://www.globalchange.umich.edu/globalchange1/current/lectures/topography/topography.html

Preview of Assessment Questions:
1. How is the Earth like the density column shown in class?
2. Why do the peaks of the Colorado Rockies never reach above 14,500 feet?
3. Discuss a change that would have to occur for the mountains to rise above 14,500
feet. There is more than one right answer to this question.

1. Get acquainted with the site.
 Scrolling down this web page, you will find the diagram below:

   The is the symbol representing density. Therefore, according to the diagram, saltwater
has a density of 1.03.
   Located directly above the diagram is a simulation called “Isostasy”. Manipulate the data