Par 5

An activity from Dave Mastie (Ann Arbor, MI)

Type of Lesson: Hands-on Activity/Discussion

Time Needed: 25 minutes

National Standards Addressed

Earth and Space Science, Grades K-4: Earth materials are solid rocks and soils, water, and the gases of the atmosphere. The varied materials have different physical and chemical properties, which make them useful in different ways, for example, as building materials, as sources of fuel, or for growing the plants we use as food. Earth materials provide many of the resources that humans use.

Earth and Space Science, Grades 9-12: The Earth is a system containing essentially a fixed amount of each stable chemical atom or element. Each element can exist in several different chemical reservoirs. Each element on earth moves among reservoirs of solid earth, oceans, atmosphere and organisms as part of geochemical cycles.

Earth and Space Science, Grades 9-12: Interactions among the solid earth, the oceans, the atmosphere and organisms have resulted in the ongoing evolution of the earth system. We can observe some changes such as earthquakes and volcanic eruptions on a human time scale, but many processes such as mountain building and plate movements take place over hundreds of millions of years.

Physical Science, Grades K-4: Objects have many observable properties, including size, weight, shape, color, temperature, and the ability to react with other substances. Those properties can be measured using tools, such as rulers, balances, and thermometers.

Physical Science, Grades 5-8: A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.

Quick Summary of Lesson

This activity could act as an introduction to a discussion on density or a discussion about the interaction between fresh water and salt water (and therefore could lead to a discussion of estuarial systems).

Materials (for each group of 2 students)

tennis ball container
Morton's water softening salt pellets - 1 cup
colored golf ball
blue food coloring


1. Have students work in groups of 2. Then have them follow these directions:
Place 1 cup Morton's water softening salt in the tennis ball container.

2. Place golf ball on top of pellets.

3. Fill container with tap water - stop 2 inches from top.

4. Cap the tennis ball container and shake for several minutes (until golf ball floats). hint: caps to tennis ball containers may not be 100% watertight, so placing a piece of paper towel over the cap while shaking is a good idea!

5. Wait a couple of minutes until salt water clears (if you're using regular salt, it won't clear).

6. Slowly add tap water on top of column (ball should sink to lower position). It is best to pour the tap water VERY SLOWLY right on top of the floating golf ball!

7. Add 2 drops blue food coloring and gently stir the coloring in. Color stops at interface of fresh/salt water.

8. Lead class discussion over some of the notes below or have students design further experiments relevant to notes below...

Notes to the Teacher

Using Morton's water softening salt will give you more bang for the buck! Other salts (pickling, kosher, normal salt) are far more expensive. If you do have these other salts on hand, the exercise will still work.

This exercise is called par 5 because it has 5 points of discussion (see further notes on these points of discussion below):
1) density of fresh versus density of salt water
2) solubility factors of salt in water
3) estuarial studies - what happens in the environment when fresh water and salt water come together?
4) color combinations - discuss complementary colors using the dye and the colored golf ball
5) experimental factors - have students design a further experiment

1)Adding a few drops of food coloring and gently stirring it it shows the students that the fresh water is less dense and is actually sitting on top of the more dense salt water. The golf ball is actually floating on the salt water and would sink through the fresh water.

2)Students could investigate how much salt can be dissolved in really cold water (close to freezing point, but not frozen) as opposed to really hot water (close or at the boiling point). More salt should dissolve in the hotter water.

3)An estuary is a system where fresh water and salt water come together. Estuaries are unique ecosystems where life thrives and unique biological interactions occur. Students could definitely research these estuarial systems in more detail.

4)This exercise actually does provide an opportunity to look at complementary colors. Complementary colors are red & green, blue & orange, and yellow & purple. If you take a blue golf ball and use orange food coloring, the part of the ball that is elevated in the fresh water will appear black (when one complementary color is viewed through the other, one sees black). If you used a green golf ball and red food coloring, the part of the golf ball elevated in the fresh water would appear black and so on...Also if you use a blue golf ball and yellow coloring, the ball immersed in coloring will look green. You can actually paint the golf balls (place golf tee through cardboard box cover and then place golf ball on top of tee to paint most easily) with crylon paint to get an assortment of colors for this exercise.

5)It is extremely hard these days to get students to make the leap into inference (a higher level of thinking according to Bloom's Taxonomy). There are lots of extension experiments that could be done that would help students answer a question related to this exercise. Have students formulate a question and then design and implement an experiment to answer their question. For example, students could look at how much salt dissolves in cold water versus hot water, they could experiment to see why different golf balls float at different levels (all American golf balls are the same size, but there insides are very different!), they could investigate organisms' reactions to the mixing of fresh and salt water...

Need More Information? Try Using Windows to the Universe

Please use these links for further ideas or more information:
Density of the Earth
Density inside the Sun
Another activity for the classroom called Diving Raisins
Energy density inside tornadoes
Groundwater cation exchange
The Ocean

Last modified March 15, 2002 by the Windows Team

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