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Almost everything that is left outside for a long time is worn down. Changes occur in the way it looks. This is called weathering. Water and wind wear down rocks over a long period of time. You see an example of this by looking at the round, smooth rocks found in rivers or streams.
 
This arch was formed over a long period of time by wind or water moving against it.
 
Sometimes rocks are broken down by plants. If a rock has a small crack in it, the plant forces its roots into the crack pushing it apart. Another way that rocks break down is by freezing. When water on the rocks freezes, it expands breaking the rocks apart.
 
TRY IT

Materials:

  • One wooden block
  • Three hard candies (any kind)
  • Three M & M® candies
  • One pair of safety glasses
  • Hammer
  • Two small clear plastic cups
Procedures:
  1. Put on the safety glasses. Place one hard candy on the wooden block, and hit it gently with the hammer. Do same thing with one M & M®. Record what happens in a science journal. (You will notice that just like igneous rocks, different kinds of candy break down in different ways.)
  2. Place one hard candy and one M & M® in the freezer for at least 15 minutes. After they are frozen, hit each candy with the hammer before they warm up. What happens? Record what happens in a science journal.
  3. Put one M & M® in one of the clear plastic cups and one hard candy in the other plastic cup. Add enough water to each cup to cover the candy. Swirl the candy around for 5 to 10 minutes. What happens to the candy? Record your findings in a science journal.
  4. Place the cups of candy and water in a safe place, and let the water evaporate. Once the water evaporates, record your findings in your science journal. What is left at the bottom of the cup represents a sedimentary rock that has been changed by weathering.
 

You can also ...

Take a plastic bottle of water and place it in a freezer. Come back later, after it is frozen, and look at the bottle. What happens to the shape of the bottle? When water freezes, it takes up more space, or expands. If the bottle is filled to the top and the lid is on tight, the ice forces the bottle to expand. When the weather outside changes to freezing cold, the water in the cracks of rocks forces the rocks apart as it changes to ice.
 

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Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 4th grade science core.


Updated October 24, 2008 by: Glen Westbroek

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