Lab / experiment Grade 11 Science

Brindle Settling Column: Measuring Settling Velocity

A grade 11 lab measuring how fast coarse and fine sediment settle in a water column, linking settling velocity to clarifier design and river deposition.

Grade: Grade 11
Subject: Science
Material: Lab / experiment
Time: 55 min
Prep: Moderate prep
Materials: Two tall clear containers, such as 1-liter graduated cylinders or straight-sided clear bottles (1 pair per group), Ruler or measuring tape marked in centimeters, Stopwatch or phone timer, Coarse sand, about 2 tablespoons per group, Fine soil such as sifted garden soil, about 2 tablespoons per group, Water, about 2 liters per group, Stirring rod, or a cap to seal and invert the container, Marker and paper towels

Standards

HS-ESS2-5 NGSS

Plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes.

How this material aligns: Students plan and carry out an investigation of how suspended particles settle through water, the water-and-Earth-materials deposition process this standard names, recording clear-zone depth against time.

All materials for HS-ESS2-5 →

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Analysis items 2 and 3 combine settled depth in centimeters with elapsed time in minutes to compute a settling velocity, choosing and interpreting consistent units.

All materials for HSN-Q.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will measure how a settling column's clear-zone depth changes over time.
Students will calculate and compare settling velocities for coarse and fine sediment.
Students will connect settling rate to particle size, clarifier design, and river deposition.

Vocabulary

Sedimentation: Sedimentation is the step where water sits almost still in a big basin so the heavy clumps of dirt can sink to the bottom. The cleaner water on top then moves on to the filters.
Deposition: Deposition is when water vapor in the air turns directly into ice without ever becoming liquid first, the way frost forms on a cold window. It is the opposite of sublimation, where ice turns straight into vapor.

Also: settling velocity, suspended sediment, particle size

Teacher overview

Before water is filtered, treatment plants let gravity pull suspended particles out of it in a settling basin, and the same physics decides whether a river carries sediment downstream or drops it in a calm lake. This lab has students build two settling columns, one with coarse sand and one with fine soil, and track how a clear zone grows at the top as particles fall, which lets them compute a settling velocity for each. The investigation is a simplified classroom analog of a clarifier, not a certified measurement. Students should see that coarse particles settle in seconds to minutes while fine particles take far longer, which is why real basins are designed for hours of detention and why the finest clay may never settle without help.

Brindle Settling Column: Measuring Settling Velocity — Grade 11 Science

Name: ____________________________ Date: ______________

Procedure

Step 1. Safety: this lab uses only clean water and soil, so the main hazards are spills and slips. Wipe up spilled water at once, keep containers away from table edges, and wash your hands after handling soil. Do not taste any material or water.

Step 2. Set the two clear containers side by side. Using the marker, label one Coarse and one Fine. With the ruler, mark a fill line about 30 centimeters up from the bottom on each, or near the top if the container is shorter, and record that starting height.

Step 3. Put about 2 tablespoons of coarse sand into the Coarse container and about 2 tablespoons of fine soil into the Fine container. Add water to the fill line in each.

Step 4. Cap or cover each container and invert it several times (or stir well with the stirring rod) to mix the sediment evenly through the water, then set it down and start the stopwatch at the moment you stop mixing. A clear zone will begin to form at the top as particles fall.

Step 5. Measure the depth of the clear zone (from the water surface down to the top of the still-cloudy suspension) in centimeters at 1, 2, 5, 10, 15, and 20 minutes, and record each reading for both containers. Take the two containers' readings as close in time as you can.

Step 6. If the coarse column clears completely before 20 minutes, record the time at which it became fully clear and keep tracking the fine column to 20 minutes.

Step 7. Do not pour sand or soil down a sink drain; let the sediment settle, then decant the clear water and dispose of the sediment in the trash as directed.

Data & Analysis

Time (min)	Coarse column clear-zone depth (cm)	Fine column clear-zone depth (cm)
1
2
5
10
15
20

On one set of axes, plot clear-zone depth (in centimeters) against time (in minutes) for both columns. Describe how the two curves differ in steepness.
Using your coarse-column data, calculate the average settling velocity over the first 5 minutes, in centimeters per minute (clear-zone depth divided by time). If the coarse column cleared completely before 5 minutes, divide the full column depth by the time it became clear (Step 6).
Using your fine-column data, calculate the average settling velocity over the first 5 minutes, in centimeters per minute.
Which sediment settled faster, and how does particle size explain the difference?
A treatment clarifier gives water 2 to 4 hours to settle. Based on your fine-column settling velocity, explain why plants need such long settling times for fine particles.
Real plants add a coagulant that clumps fine particles into larger clusters before settling. Predict how that clumping would change your fine-column settling velocity, and explain why.
Explain why a fast-moving river carries fine sediment far downstream while a still lake lets it settle out, using your settling-velocity results as evidence.
Identify one source of measurement error in your procedure, and state whether it would make your calculated settling velocity look too fast or too slow.

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 coarse curve rises more steeply than the fine curve.
Accept any description in which the coarse column's clear zone deepens quickly and then levels off, while the fine column's clear zone deepens slowly; the coarse curve is steeper because its particles fall faster.
Answer: the coarse column's settling velocity over the first 5 minutes.
Accept any value equal to the student's own 5-minute clear-zone depth divided by 5 minutes, reported in centimeters per minute. If the coarse column cleared completely before 5 minutes, accept the full column depth divided by the time it became clear (Step 6). Coarse sand typically clears several centimeters per minute or faster.
Answer: the fine column's settling velocity over the first 5 minutes.
Accept any value equal to the student's own fine-column 5-minute depth divided by 5 minutes, in centimeters per minute; it should be much smaller than the coarse-column value.
Answer: The coarse sand settled faster.
Larger, denser particles fall faster through water because their weight overcomes drag more easily, while fine particles have more surface area relative to their weight and sink slowly; accept any answer that ties the faster settling to larger particle size.
Answer: Fine particles settle so slowly that hours are needed.
Because the fine-column velocity is very small, fine particles would need a long fall time to reach the bottom of a deep basin, so plants provide 2 to 4 hours of detention to give them time to settle before the water moves to the filters.
Answer: Clumping would speed up settling.
Coagulant joins many fine particles into a larger, heavier floc that behaves like a coarse particle, so the settling velocity would increase; accept any prediction of faster settling justified by the larger effective particle size.
Answer: Moving water keeps fine particles suspended; still water lets them fall.
The lab shows fine particles settle slowly, so in a fast river the water moves them downstream before they can reach the bottom, while in a still lake there is no current to keep them up and their slow settling eventually drops them out.
Answer: a reasonable error source and its direction.
Accept any genuine source, such as reading the cloudy boundary too low (making the clear zone look deeper and the velocity too fast), starting the timer late, or uneven mixing; the answer must state whether the error raises or lowers the measured velocity.

Differentiation

Support

Pre-mix one demonstration column so students see what a growing clear zone looks like before they judge their own, and provide a data table with the time intervals already filled in so students only record depths. Give the settling-velocity formula with labeled blanks for depth and time.

Extension

Have students test a third column of mixed coarse and fine sediment, predict whether its clear zone will grow like the coarse column, the fine column, or somewhere between, then use their data to explain the two-stage settling they observe.

ELL supports

Pair the terms "settle," "clear zone," "coarse," and "fine" with a labeled picture of a column showing clear water on top and cloudy suspension below. Allow students to record depths as numbers in the table and to answer items 4 through 8 with short phrases using sentence frames.