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Project Summary

Difficulty	2
Time required	Very Short (a day or less)
Prerequisites	None
Material Availability	Readily available
Cost	Very Low (under $20)
Safety	No issues

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Abstract

Objective

In this experiment you will test if the porosity of a rock matrix is affected by particle size.

Introduction

Did you know that rocks are not completely solid? Rocks have tiny pockets of air inside them. This is obvious when you look at a piece of volcanic rock, but it happens in dense rocks like granite, too. It's just that the pockets of air are very small.

You will notice that if you pick up same-sized pieces of volcanic rock and granite, that they do not weigh the same. The granite feels heavier than the volcanic rock. The holes of air in the volcanic rock make it feel lighter because it is more porous and less dense. The granite is less porous and more dense. The porosity of a rock can be used to characterize the rock and identify what type of rock it is.

Imagine that a rock is made up of tiny particles of minerals and crystals that are packed together. In between the particles there will be extra space which is filled with air and gas. The size of the particles will affect the way that they pack together in a certain amount of space. Larger particles will not pack together as well as small particles, leaving more room for air and gas between the particles and making the rock more porous.

In this experiment, you will investigate the effect of particle size on porosity by making a model to test your hypothesis. Which particles will leave the most space and make a more porous matrix, small particles or large particles?

Terms, Concepts and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• rocks
• minerals
• crystals
• porosity
• particles
• density

• How is porosity related to particle size?
• How much space is left between particles of rock or soil?
• How can porosity be measured?

Bibliography

• SEED, 2006. "Porosity," Schlumberger Excellence in Educational Development (SEED) program, Schlumberger Ltd. [accessed: 4/26/06]
  http://www.seed.slb.com/en/scictr/lab/porosity/index.htm
• Wikipedia contributors, "Porosity," Wikipedia, The Free Encyclopedia. [accessed: 4/26/06]
  http://en.wikipedia.org/w/index.php?title=Porosity&oldid=49469765
• Brynie, F.H., 2005. Parent's Crash Course: Elementary School Science Fair Projects, Hoboken, NJ: Wiley Publishing Inc. pp 165-168.

Materials and Equipment

• clear plastic cups
• water
• permanent marker
• measuring cup
• differently-sized rock particles

Experimental Procedure

1. First, you will need to find your rock particles. You will want 4-6 differently sized samples of rock. You can often buy these from a landscape or construction supply store. They sell crushed granite in different sizes. Get some large-, medium-, small-, and fine-grade samples.
2. Fill each clear plastic cup with each of your samples. Label each cup with the size of the particles in the sample.
3. Fill your metric measuring cup with water to the 100 mL mark.
4. Pour water into the first sample until it is full to the rim of the cup. Pour slowly and gently so you do not spill water out of the measuring cup, as this will cause error in your measurement.
5. Record the amount of water left in the measuring cup. It should be less than 100 mL. Write your result in a data table:

   Grain Size	Water Before (mL)	Water After (mL)	Volume Displaced (mL)
   Large
   Medium
   Small
   Fine

6. Now calculate the amount of empty space in the sample by subtracting the amount of water you measured from 100 mL. For example, if after pouring water into your cup you were left with 60 mL of water, then you would subtract 60 mL from 100 mL to get 40 mL. This means that there is a volume of 40 mL of space between the particles in your cup.
7. Repeat steps 2-6 for each sample.
8. Make a graph of your data to compare your results.
9. Which particle size had the most amount of empty space? The least amount of space? Was there a pattern to your data? Does this reveal any relationship between particles size and pore space?

Variations

• Here you used differently sized pieces of the same material, crushed granite. What about other materials and minerals? Try comparing different types of crushed rock like volcanic rock, gravel, quartz, sandstone, or limestone.
• Soil is a mixture of rocks, minerals and organic matter. Porosity is also a property of soil. Try the same experiment using different types of soil: clay, loam, sandy, silty, potting soil, compost, etc. The only thing to do differently is place a screen on top of the cup to keep organic matter from floating out as you pour the water into the cup. Do different types of soils have different porosities?
• Porosity can also be linked to the soil type, amount of compaction and dryness of the soil. Try these other Science Buddies experiments too:
  • Soil Color and Moisture
  • Measuring Soil Compaction

• For more science project ideas in this area of science, see Geology Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Last edit date: 2006-08-15 17:10:45

Career Focus

If you like this project, you might enjoy exploring careers in Geology.

	Geoscientist Just as a doctor uses tools and techniques, like x-rays and stethoscopes, to look inside the human body, geoscientists explore deep inside a much bigger patient—planet Earth. Geoscientists seek to better understand our planet, and to discover natural resources, like water, minerals, and petroleum oil, which are used in everything from shoes, fabrics, roads, roofs, and lotions to fertilizers, food packaging, ink, roads, and CD’s. The work of geoscientists affects everyone and everything.			Petroleum Engineer Earth is our home and is the source of everything that we require to survive and thrive. Earth gives us food, shelter, and energy. One source of energy, found deep within the earth, is oil. Oil drives the world's economy and is an extremely important commodity. Petroleum engineers spend their careers searching for reservoirs of oil and developing methods to efficiently extract it from the earth without damaging the surrounding environment.
	Geographer When you hear the word geography, you might think of maps and names of state capitals, but the work of geographers is much more than creating maps and identifying places. Geographers look at how people, places, and Earth are connected. They study the economy, social conditions, climate, and topography of a region to help answer questions in urban and regional planning, business, agriculture, and medicine.			Mapping Technician Essential members of any construction team include mapping and surveying technicians—the “instrument people”—who set up and operate special equipment that measures distances, curves, elevations, and angles between points on Earth’s surface. These technicians then take the data gathered by the instruments and create maps and charts on a computer. About half of their work is spent in hands-on, high-technology data collection in the field, while the other half is spent in an office—they get to experience both worlds and create documents that define, in great detail, places on Earth.
	Soil Scientist Not all dirt is created equal. In fact, different types of soil can make a big difference in some very important areas of our society. A building constructed on sandy soil might collapse during an earthquake, and crops planted in soil that doesn't drain properly might become waterlogged and rot after a rainstorm. It is the job of a soil scientist to evaluate soil conditions and help farmers, builders, and environmentalists decide how best to take advantage of local soils.			Hydrologist Water is critical to the survival of virtually all the living things that you see around you. It is essential to the production of most of the things that people make, too. Hydrologists are the people who study and manage this remarkable resource. Through data gathered from satellite instruments, hydrologists examine and create computer models that show how water moves above, on, and under the earth. With these models, hydrologists work to conserve water, to predict droughts or floods, to find new water sources, and to reduce and reuse waste water.

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