Darcy's law Activities

Video Demonstration

Video showing the gist of the procedure

Materials

•          5/6mm MDF Sheet (See File)

•          6kg Sand, fine grain gravel

•          300x300x6mm Transparent Acrylic

•          Water

•          Food Colouring (Optional)

•          Wood Glue

•          Superglue

•          Joint Sealant

Construction:

1. Glue the MDF sides and back to the base with wood glue and allow to dry.

2. Ensure joint sealant is applied to the wooden frame to prevent water seeping through and allow to dry.

3. Once the sealant has set, rest the assembly on the back and glue the two slots a little over 6mm apart. This is so that the dam section can be adjusted in height. Use an engineering square to ensure the slots are perpendicular to the surface. Leave to dry.

4. Use superglue to fix the clear acrylic to the front of the assembly. Sealant may             also be used here.

5. Finally Slide the dam section into the slots with the handle end sticking out at the     top. This enables the height of the dam to be changed easily.

Preparation Note - Before starting the experiment place plastic lining or cloth underneath the container to catch any spillage of sand or water, appropriately seal sides of slider.

Procedure 

1. Adjust the height of the dam section to a desired height. (Depending on how well the unit was assembled this section should be held firmly in place by friction. If it is too tight file/sand the slots down slightly. If it is too loose use a peg to hold it in place.)

2. Fill the container with sand until the desired height. The height should be higher      than the base of the dam section by at least 10mm. The distance the water must travel has an impact on the rate of water seepage based on Darcy’s Law:

So the greater the distance, the less seepage occurs. This length l equals the height of sand on the left side, add the sand height on the right hand side and the thickness of the dam section (e.g. 6mm)

3. Carefully pour the water to the left-hand side of the container. (Food colouring may be added prior and mixed to consistent colour. Adding colour helps visualise the flow of water). Water should be poured or gently pumped through a pipe to minimise force down on the sand when adding it. The level of the water either side should be marked with a whiteboard pen as soon as the water rushes through. This point is the failure of the dam.

4. Using the difference in water level height and length (calculated in 2) an estimate for K can be calculated by estimating how much water was added and how long it took from the point of failure until the water levels are equal. This is usually only a couple of seconds.