Teacher Site Map
7th Grade Core
Science Home Page
USOE

Have you ever come across a smooth pond like the one above? It just seems to ask you to "skip a rock on the surface!" You know that when the rock stops skipping, it will sink beneath the surface. What makes rocks sink while leaves or twigs float in water? It's density!

Remember the properties of moving water. Dense objects like large rocks stay at the bottom while lighter objects like silt and dirt can be carried away by the flow. Density affects the sorting of naturally occurring materials in a mixture.

In this activity, you will demonstrate how materials can naturally sort based on their density.

Materials:

  • Container with a lid
  • Various naturally occurring objects of different densities (e.g. sand, gravel, leaves, twigs, etc. Make sure that you try not to include any man-made materials!)
  • Water

Procedure:

  1. Put all of the objects in the container.
  2. Fill your container with water until it is almost full.
  3. Tightly put the lid on your container.
  4. Shake your container up!
  5. Let your container sit without you touching it.
  6. Observe the settling pattern of the objects.

Safety concerns: icon Be sure to follow all glassware, and chemical object safety rules that are specified by your teacher in all general laboratory experiences. As with all science lab activities, the most important safety rule is to follow all teacher directions.

Observations:

  1. Draw a picture the container just after you finish shaking it.
  2. Carefully observe your experiment.
  3. Record your data.
Layer
Description
Time to settle out
Lowest    
Middle    
Top    
  1. Draw a picture of the jar after it has finished settling.


Analysis:

  1. How much faster did the first layer settle than the last layer settle?
  2. Are there objects which move to the top?
    • How would you describe these objects?
  3. How does this activity relate to the structure of a riverbed?
  4. In a riverbed, where would you expect to find the biggest rocks?
    • Explain your answer.
  5. In a river, why do you find sand and mud around slow moving water?

Review science lab safety rules here.

Get the plug-ins: Get Adobe Acrobat Reader , and Get Quicktime Player. (The QuickTime plug-in is needed to play sounds and movies correctly.)

Want to share a photograph of you or your friends doing this activity? Send the photograph attached to an e-mail with the following information: the title of the activity, the URL (Internet address), and your name. Remember that no pictures can be used which show any student faces or has a student name on it.

Updated August 11, 2005 by: Glen Westbroek

Science Home Page | Curriculum Home Page | 7th Grade Science Core Home Page | USOE Home Page

Copyright © Utah State Office of Education.