Classroom activity Grade 9 Science

Frost Wedging and Winter Main Breaks in Grangemoor

A grade 9 four-station rotation investigating why water expands on freezing and how frost depth, not air temperature alone, drives a city's winter main breaks.

Grade: Grade 9
Subject: Science
Material: Classroom activity
Time: 55 min
Prep: Moderate prep
Materials: Six 50 mL graduated plastic tubes, three filled to 40 mL with water and frozen the day before, Six small plaster-of-Paris blocks, three soaked to saturation and three kept dry, all frozen and thawed twice before class, Balance reading to 0.1 g, Weigh boat for collecting shed fragments at Station B, Clear tube of moist silty soil, sides wrapped in insulation, frozen overnight in a freezer, Metric ruler and calipers, Printed student handout and data card for each student, Graph paper for the Station D plots

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 conduct frost-wedging and freezing-expansion investigations of water acting on porous solids and soil, which is the mechanical investigation this standard names.

All materials for HS-ESS2-5 →

RST.9-10.3 Common Core ELA

Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.

How this material aligns: Each station hands students a written procedure to follow exactly, including the freezing-tube special case where the mark is read only after the ice stops rising, and stations 2 and 4 depend on that precision.

All materials for RST.9-10.3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-04.

Objectives

Students will measure the volume change of water on freezing and relate it to a change in density.
Students will compare frost damage in saturated and dry porous solids and identify the variable responsible.
Students will use a utility's frost-depth record to explain why main breaks peak after the coldest month.

Vocabulary

Key words: frost wedging, frost depth, saturation, density, frost heave, lag

Teacher overview

This is a four-station rotation for groups of four to six students, run in one period after the teacher prepares the frozen samples a day ahead. Each station isolates one link in the chain that connects a physical property of water to a broken water main: the expansion of water on freezing, the wedging apart of a saturated porous solid, the heaving of soil as ice lenses grow, and a fictional utility's record of frost depth and main breaks across one winter. Students routinely explain winter main breaks by saying that cold makes metal brittle, which is only part of the story, and the rotation is arranged so that the frost depth record forces them to account for the ground rather than the air.

Activity Directions

Prepare the day before (20 minutes of teacher time). Fill three 50 mL graduated tubes to the 40 mL mark with water, cap them loosely, and freeze them upright. Soak three plaster blocks in water until no more bubbles rise, leave three dry, and put all six through two freeze-and-thaw cycles. Pack the clear tube with moist silty soil, mark the soil surface with a fine line, wrap its sides in insulation, and stand it upright in a freezer overnight so it freezes from the top down; bring it out at the start of class. Keep three unfrozen tubes of water at room temperature as the comparison at Station A.
Frame the question (5 minutes). Tell the class that the fictional Grangemoor Water Department repairs more broken mains in some winter months than others, and that the department wants to know what the breaks track.
State the rotation rule: 10 minutes per station, four stations, handout completed as they go.
Station A, the volume of freezing (10 minutes). Groups read the volume of a frozen tube against the volume of a matched liquid tube, then mass both tubes on the balance. They record both readings on the handout and answer items 1 through 3.
Station B, wedging a porous solid (10 minutes). Groups compare the three saturated blocks with the three dry blocks after two freeze-thaw cycles, counting visible cracks and collecting shed fragments on a tared weigh boat. Before they look closely, each group writes down which set it predicts will shed more and why. They answer items 4 and 5.
Station C, frost heave in soil (10 minutes). Groups measure how far the soil surface has risen above the marked line and examine the tube from the side for pale horizontal bands of ice. They answer item 6.
Station D, the utility record (10 minutes). Groups plot main breaks against maximum frost depth from the data card, then plot breaks against mean air temperature, and compare the two relationships. They answer items 7 through 9.
Debrief (5 minutes). Bring the class together and ask two questions. First, which station explained the force that cracks a pipe, and which explained the timing of the breaks? Second, why does the peak in breaks fall in February rather than in January? Use a quick hand poll on the second question as the formative check, and continue the discussion if fewer than three-quarters of the class connects the answer to the depth of the frost line rather than to the temperature of the air.
Close (5 minutes). Students complete item 10 individually and turn in the handout as the exit ticket.

Frost Wedging and Winter Main Breaks in Grangemoor — Grade 9 Science

Name: ____________________________ Date: ______________

Student Handout

Record your measurements as you go. Items 1, 2, and 6 depend on what your group measures, so your numbers may differ from another group's.

Station A. The frozen tube began as 40 mL of liquid water.

Read the top of the ice in the frozen tube. What volume does it occupy, in milliliters?
Calculate the percent change in volume from 40 mL to the volume you read.
Your two tubes have the same mass but different volumes. What does that tell you about the density of ice compared with the density of liquid water?

Station B. Three blocks were soaked to saturation and three were kept dry. All six went through the same two freeze-and-thaw cycles.

Which set of blocks shed more fragments, the saturated set or the dry set?
Explain the difference using what you measured at Station A about water inside the pore spaces of the block.

Station C. The soil surface was marked with a line before the tube went into the freezer.

How far has the soil surface risen above the marked line, in millimeters?

Station D. The table below is one winter of records from the fictional Grangemoor Water Department. Maximum frost depth is the deepest the freezing front reached below the ground surface during the month.

Month	Mean air temperature (degrees F)	Maximum frost depth (inches)	Main breaks repaired
November	41	0	4
December	30	9	11
January	19	26	34
February	23	31	41
March	36	18	22
April	48	0	7

Which month had the most main breaks?
Which month had the lowest mean air temperature?
Your answers to items 7 and 8 are different months. Explain why the breaks peak in a month that is not the coldest, using the frost depth column.
In three steps, explain how the property of water you measured at Station A ends in a cracked water main under a Grangemoor street.

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: accept any reading between 42 and 45 mL.
Water that filled 40 mL as a liquid expands to roughly 43 to 44 mL as ice. Readings vary with how much air was trapped and how the meniscus froze, so accept anything in the stated range and ask groups outside it to check whether the tube was filled to the mark.
Answer: accept any value between 5 and 12.5 percent.
Percent change is the volume read minus 40, divided by 40, times 100. A reading of 43.5 mL gives 3.5 divided by 40, or about 9 percent.
Answer: ice is less dense than liquid water.
Density is mass divided by volume. The mass did not change and the volume increased, so the density of the ice must be lower. This is unusual, because most substances contract as they solidify.
Answer: the saturated set.
The soaked blocks shed noticeably more fragments and show more visible cracks than the dry blocks after the same two cycles.
Answer: water in the pores expands as it freezes and pushes the pore walls apart. Station A showed that freezing water takes up more space than the same mass of liquid. Inside a saturated block, that expansion has nowhere to go, so it presses outward on the walls of each pore. Repeating the cycle widens the cracks a little each time. The dry blocks contain almost no water to freeze, so nothing pushes on the pore walls.
Answer: accept any measured rise between 2 and 15 mm.
The surface rises because ice lenses grow in the soil and lift everything above them. Groups should also report seeing pale horizontal bands, which are the lenses themselves.
Answer: February.
February recorded 41 main breaks, the highest month in the table.
Answer: January.
January had a mean air temperature of 19 degrees F, the lowest in the table.
Answer: breaks follow frost depth, which keeps deepening after the coldest month. Air temperature acts on the ground surface, and the freezing front takes weeks to work downward. Frost depth in the table reaches 26 inches in January and 31 inches in February, so the frozen ground is deepest in February even though the air was colder in January. Buried pipes feel the frost line, not the air, so the breaks peak with the frost depth.
Answer: water expands on freezing, the expansion moves soil and loads the pipe, and the loaded pipe cracks. A full three-step answer should say that water freezing in soil pore spaces expands, as measured at Station A; that the expansion heaves and shifts the soil around a buried main, as seen at Station C; and that the shifting soil puts bending and shear loads on a pipe that is already brittle with age and chilled by the water inside it, until the pipe cracks. Accept an answer that names expansion, ground movement, and pipe loading in that order.

Differentiation

Support

Give these students the Station A calculation partly worked, with the subtraction shown and only the division and multiplication left, and hand them a prepared graph grid for Station D with both axes already labeled and scaled. Pair them with a partner who reports the measurements aloud while they record.

Extension

Ask students to design a fifth station that would test whether pipe material matters, naming the variable they would change, the variable they would hold constant, and the measurement they would take. Have them explain why the Grangemoor record alone cannot separate the effect of pipe material from the effect of frost depth.

ELL supports

Pre-teach frost wedging, saturation, density, and frost depth with a labeled cross-section showing a street, the frost line, and a buried pipe. Provide the handout items with sentence frames such as "The saturated blocks shed ___ fragments than the dry blocks because ___." Allow groups to answer orally to the teacher before writing.

Extensions

Have students request or look up the frost depth used for pipe burial in their own region's plumbing code, then write a short note explaining why the required burial depth differs between a northern and a southern state. Ask them to predict what the fictional Grangemoor break record would look like in a winter whose frost depth never exceeded the burial depth.