Lesson Plan

Castles in the Sand

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Grade Level:
First Grade-Adult Education (general)
Chemistry, Hydrology, Physical Science
45 minutes
Group Size:
Up to 36 (6-12 breakout groups)
National/State Standards:
Science: 1st grade 1.1; 2nd grade 1.1; 5th grade 1.1


Students will learn about the cohesive force of water tension and the adhesive force of capillary action.


Students will learn about the cohesive force of water tension and the adhesive force of capillary action.


One of the more special properties of water is its 'stickiness'. Because of attractive intermolecular forces, water beads up on waxy surfaces, it travels upwards through the trunk of a tree, and insects are able to walk across its surface.

Two types of forces contribute to water's stickiness: cohesive and adhesive forces.

Cohesive forces create the attraction between individual water molecules. These forces contribute to surface tension. Surface tension allows water strider insects to move almost effortlessly across a creek's surface without sinking. Surface tension keeps water from quickly evaporating from lakes. Without surface tension, the morning dew could not bead up on spider webs.

Through adhesive forces, water is attracted between unlike molecules. Look closely at water rising up the sides of thin a glass tube. This adhesive attraction is even greater than water's cohesive force (which causes surface tension). Water's adhesion to other surfaces, such as sand grains, causes a flow called capillary action. Capillary action helps water rise to the top of the highest trees, helps water flow through some aquifers, helps transport nutrients throughout your body, and allows the billions of sand grains in a sand castle to stick together.

Explore Great Sand Dunes' web page on hydrology for more on the interaction of water and sand in the park.



Various buckets, cups, scoops, and small shovels



Make a list of things in nature or things made by people that would not work without surface tension or capillary action.



Sand Filters is a follow-up activity that helps students understand how capillary action filters water naturally.


capillary action, surface tension

Last updated: February 24, 2015