Density, Gravity and Motionless Balanced Floating

Name ______Date ______

Activity 4 – Isostasy

How can we relate the density of an object to how high it floats in a fluid?

INITIAL IDEAS

You have probably heard or seen pictures of icebergs floating in the ocean. On your own, why do you think icebergs float? Be sure to include density in your answer.

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You’ve also probably heard the expression the “tip of an iceberg.” Why do you think that more of an iceberg sits below the surface of the ocean (the water line) than above it?

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Be prepared to share your answers with the class.

Collecting & Interpreting Evidence

Name ______Date ______

Experiment 1 – How does the density of an object affect how high it will float in a fluid?

Your group will need:

  • One wood block
  • Small bucket to float the wood block
  • Water
  • Gram balance
  • Ruler
  • Calculator
  • Grease pencil
  1. Determine the density of your wood block. (Calculate the density in g/cm3.)
  1. Float your wood block in your bucket of water and mark the water line (known as equilibrium line).
  2. Draw an exact sketch of the side view of you wood block and show the exact position of the waterline (equilibrium line). Label the total height of the wood block (Hblock), the height of the wood block that is below the waterline (Hbelow), and the height of the wood block that is above the waterline (Habove).
  1. Measure and record Hblock ______cm
  2. Measure and record Hbelow ______cm
  3. Measure and record Habove ______cm

The next several steps require kids to calculate the above for several different density blocks of wood. Kids will see that the ratio of Habove to Hbelow is closely related to the density of an object. This seems a very cool thing to do but also seems very abstract. I guess we can start it and it can be continued in HS.

Table 2-3

MASS (g) / VOLUME (cm3) / DENSITY (g/ cm3) / Hblock / Habove / Habove/
Hblock / Hbelow / Hbelow/
Hblock / % BELOW
Block 1
Block 2
Block 3
Block 4
Block 5
Block 6
Block 7
Block 8

Density, Gravity and Motionless Balanced Floating

Name ______Date ______

Activity 5 – Isostasy and Earth’s Global Topography

How can we relate the density of rocks to the topography of the Earth?

INITIAL IDEAS

Once again, look at the 3-D map with the 3-D glasses. Write down some large-scale observations you make from looking at this map that include information about patterns in elevation of Earth’s surface (i.e., oceans vs. continents). Make sure you are recording observations rather than inferences.

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In your group share and discuss these observations. Choose one or two to share with the whole class.

Collecting & Interpreting Evidence

Name ______Date ______

Experiment 1 – How does the density of Earth rocks vary?

Your group will need:

  • Gram balance
  • Large graduated cylinder (500 ml)
  • Water
  • Small samples of basalt, granite and peridotite rock
  1. Using the techniques you’ve learned, measure the densities of your rock samples. Basalt is a volcanic rock that covers the floor of the oceans. Granite is a rock that covers much of the continents. Peridotite is the rock that makes up most of the deep interior of the Earth (Earth’s mantle).
  2. Basalt (ocean floors): ______g/cm3
  1. Granite (continents): ______g/cm3
  1. Peridotite (mantle): ______g/cm3

Group / Weight (g) / Volume (cm3) / Density (g/ cm3)
1
2
3
4
5
6
7
8
9
10
World Average