Science Fair Project:

Examples of Mechanical Weathering

3.5 based on 95 ratings

Examples of mechanical weathering are easy to find in your own neighborhood. Look for cracks in the sidewalk caused by heating and cooling. Underlying tree roots can make whole slabs of sidewalk buckle. Old gravestones are often hard to read because weathering has worn away the letters.

Another concept related to weathering is erosion. Erosion is the movement of weathered materials to new places. Water, wind, gravity, and glaciers (rivers of moving ice) all cause erosion. Have you visited or seen picture of the Grand Canyon is Arizona? Over millions of years, water, wind, heat and cold weathered the rock, which was ultimately carried away by the Colorado River.

Finding evidence of weathering is fun, but it’s even more fun to cause weathering yourself!

Problem

How can we model mechanical weathering?

Materials

  • Disposable plastic cup
  • Disposable plastic spoon
  • 6 tablespoons of plaster of Paris (available at hardware stores)
  • Goggles or other protective eye ware
  • Tablespoon
  • 3 tablespoons cool water
  • Four bean seeds
  • Paper towel
  • Spray bottle

Procedure

  1. Presoak the bean seeds in water overnight.
  2. Cover your work area with newspaper, or work outside.
  3. Use the tablespoon to measure 6 tablespoons of plaster of Paris into the plastic cup.
  4. Using the disposable spoon to stir and your measuring spoon to measure, add one tablespoon of water at a time to the plaster of Paris, stirring after each addition, until you have added 3 tablespoons all together. Why don’t you add the water all at once?
  5. If your mixture still seems dry after you added all the water, add a teaspoon of water at a time until the mixture is a thick, smooth liquid.
  6. Tap the cup on the table to settle the contents, and tidy the sides.
  7. Carefully watch the plaster until it begins to solidify.
  8. Once the plaster of Paris begins to solidify, insert your four beans so that 2/3 of each bean is embedded in the plaster.
  9. Let the plaster solidify completely.
  10. Fold a paper towel in half twice.
  11. Moisten the paper towel until it is damp, but not dripping wet.
  12. Place the paper towel on top of the bean seeds to water them.
  13. Place the cup in a sunny window.
  14. Make sure to keep the paper towel moist.
  15. Observe both the growth of the bean plants and plaster.

Results

As the beans seeds sprout, they crack the plaster, just as tree roots can eventually crack a sidewalk.

Why?

When making the plaster, you did not add all the water at once because you can make a more uniform mixture if you add it slowly. If you added the beans to plaster when it was still soupy, they may have gotten pushed or sunk to the bottom.

In your investigation, you got to see mechanical weathering in action. The growing plant root and stem pushed open bigger and bigger cracks. Water was able to move in, enlarging the cracks even further. The warming and cooling of the plaster caused it to expand and contract, further weakening the overall plaster “rock”. There was likely some chemical weathering in action, too. The growing bean seeds released substances that chemically broke the plaster down.

Once you are done with your experiment, you might move your sprouting bean plants to some soil. To do this, just crack the plaster a bit more. As you dig a hole to plant your beans in the soft earth, thank the process of weathering for having started the process of turning giant boulders in fertile soil, millions of years ago!

Author: Beth Touchette
Disclaimer and Safety Precautions

Education.com provides the Science Fair Project Ideas for informational purposes only. Education.com does not make any guarantee or representation regarding the Science Fair Project Ideas and is not responsible or liable for any loss or damage, directly or indirectly, caused by your use of such information. By accessing the Science Fair Project Ideas, you waive and renounce any claims against Education.com that arise thereof. In addition, your access to Education.com's website and Science Fair Project Ideas is covered by Education.com's Privacy Policy and site Terms of Use, which include limitations on Education.com's liability.

Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety.

How likely are you to recommend Education.com to your friends and colleagues?

Not at all likely
Extremely likely