Lab / experiment Grade 4 Science
Timing How Fast Quillen Bend's Muddy Water Clears
A two-session grade 4 lab timing how sand, garden soil, and clay settle out of shaken jars, then linking the results to the settling basin at a water plant.
Objectives
- Students will observe which soil materials settle first when muddy water is left still.
- Students will record settling times and measure the settled layers in centimeters and millimeters.
- Students will explain why a water plant lets river water sit still before it is filtered.
Vocabulary
Key words: settle, sediment, clay, layer, basin
Teacher overview
After a storm, the river at the fictional town of Quillen Bend runs brown for days, and the plant that treats the town's drinking water holds that water in a long still basin before sending it to the filters. This lab puts the same process in three jars so students can see which parts of the mud drop out quickly and which stay floating for hours. The investigation question is whether every kind of soil settles at the same speed. Many fourth graders predict that all of the soil will settle at about the same speed, and the clay jar gives them a clear result that argues against that prediction. The lab runs across two sessions because the clay needs to sit overnight before there is anything worth reading.
Procedure
Step 1. Put on goggles and set out three jars. Label the jars 1, 2, and 3 with the marker.
Step 2. Fill each jar with water. Fill each one about three quarters full. Use the same amount of water in all three.
Step 3. Add the soil. Put two spoons of sand in Jar 1. Put two spoons of clay in Jar 2. Put one spoon of sand, one spoon of garden soil, and one spoon of clay in Jar 3.
Step 4. Close the lids all the way. Press each lid down and twist it tight. Hold the lid with one hand while you shake.
Step 5. Shake all three jars for ten seconds. Set the jars down on the table. Start the stopwatch as soon as they are down. Do not move them again.
Step 6. Watch all three jars for two minutes. Write down the time when the first layer shows at the bottom of each jar. Write down what the first layer in Jar 3 is made of.
Step 7. Check the letter card after ten minutes. Tape the card behind each jar. Look through the water at the letter. Write yes or no for each jar.
Step 8. Leave the jars still overnight. Do not bump the table. Do not shake the jars again.
Step 9. Read the jars the next day. Look at the letter card through each jar and write yes or no again. Then hold the ruler beside Jar 3 and measure the layers at the bottom.
Step 10. Clean up. Pour the muddy water outside, not down the sink. Wash the jars. Wash your hands. Never taste the water or the soil in any jar.
Data & Analysis
Fill in the table as you go. The letter card rows take a yes or a no.
| What we recorded | Jar 1: sand | Jar 2: clay | Jar 3: mixed |
|---|---|---|---|
| Seconds until the first layer showed | |||
| Could you read the letter after 10 minutes? | |||
| Could you read the letter the next day? | |||
| Height of the bottom layer the next day |
In Jar 3, which material made a layer at the bottom first?
How many seconds did the sand in Jar 3 take to reach the bottom?
Could you read the letter through Jar 1 after ten minutes?
Could you read the letter through Jar 2 after ten minutes?
Which jar was clearer the next day, Jar 1 or Jar 2? Use two rows of your table as your reason.
Measure all the settled layers at the bottom of Jar 3 together, to the nearest centimeter. Then write that same length in millimeters.
A water plant lets river water sit still in a long basin before the water goes to the filters. Use your results to explain why.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
Answer: The sand.
Sand grains are the largest and heaviest bits in the jar, so they drop to the bottom first and form a pale layer under the darker soil. Accept sand named on its own or named as the bottom layer.Answer: Accept the group's own time.
Most groups record somewhere between five and thirty seconds. A group that recorded a full two minutes probably watched for the water to clear rather than for the first layer to appear.Answer: Yes, in most trials.
Sand settles quickly, so the water above it usually clears enough to read the card within ten minutes. Accept a no if the group stirred up the jar by moving the table, and have them note that in their table.Answer: No.
Clay stays floating in the water for hours, so the letter is still hidden after ten minutes. This is the result the lab is built to produce.Answer: Jar 1, the sand jar.
A full answer cites two rows, such as the sand jar reading yes at ten minutes and yes the next day while the clay jar read no at ten minutes and stayed cloudy or barely readable the next day.Answer: Accept the group's own measurement in both units.
The millimeter number is the centimeter number times ten. A layer of 1 centimeter is 10 millimeters, and a layer of 2 centimeters is 20 millimeters.Answer: Sitting still lets the heavy bits drop out before the water reaches the filters.
Accept any answer explaining that the basin removes the material that settles on its own, which leaves less for the filter to catch. Stronger answers add that the finest clay does not settle quickly, which is why the plant still needs filters afterward.
Differentiation
Support
Prepare these groups' jars ahead of time so their work begins at the shaking step, and give them a data table with the first column already labeled. Provide a printed timing strip marked at ten, twenty, and thirty seconds so they can circle a range rather than read a stopwatch. Measure the layers alongside them and let them read the ruler aloud before writing.
Extension
Ask students to add a fourth jar holding the same mix as Jar 3 plus a half spoon of powdered alum, shake it with the others, and compare how fast it clears, which is what a plant does when it adds a coagulant. A second task is to predict what the jars would look like after a week and to explain the prediction using the settling times they recorded.
ELL supports
Pre-teach settle, layer, clay, and clear with a labeled diagram of a jar showing bands of sand, soil, and cloudy water. Provide the data table with a small picture in each column header. Give sentence frames for questions 5 and 7: "Jar ___ was clearer because ___." and "The plant lets the water sit still because the ___ bits ___."
Extensions
Have an adult collect a jar of water from a local creek or a puddle after a rainstorm, let it stand beside the class jars, and compare how long that water takes to clear. Students can also ask their utility whether its plant uses a settling basin, since many groundwater systems skip that step entirely because well water arrives with almost no sediment in it.