Lesson plan Grade 8 Math
Marram Dunes Pump Station: Reading and Sketching Tank-Level Graphs
A 50-minute grade 8 lesson where students read and sketch qualitative graphs of a fictional pump station's tank level rising, holding, and falling over a day.
Objectives
- Students will describe how a tank's water level changes over a day by reading a graph.
- Students will sketch a graph that matches a verbal description of a tank filling, holding, and draining.
Vocabulary
Key words: qualitative graph, increasing, decreasing, constant
Teacher overview
Operators at the fictional Marram Dunes pump station watch a screen that graphs the storage tank's water level all day. The line rises while pumps fill the tank, stays flat when inflow matches demand, and falls when the town draws water faster than the pumps add it. This lesson teaches students to read and sketch those graph shapes without needing exact numbers. Because the graphs are qualitative, students focus on whether the line is going up, staying level, or coming down, and how steep it is, rather than on reading off values.
Procedure
Hook (5 min): Project a simple line that rises, flattens, then falls, labeled "tank water level" going up and "time of day" going across. Ask students to tell a story that matches the shape. Take two or three answers without saying which is right.
Direct instruction (12 min): Name the three basic pieces of a tank-level graph: increasing (filling), constant (holding steady), and decreasing (draining). Sketch each piece and connect it to what the pumps and the town are doing. Show that a steeper rising line means the tank is filling faster, and a steeper falling line means the town is drawing water faster.
Guided practice (13 min): As a class, sketch a graph from this description of the Marram Dunes tank: it fills steadily overnight, holds steady through the morning, then drops sharply in the early evening when people get home. Have students point out which part is steepest and why. Ask a check-for-understanding question: "If the line is flat, is water still moving through the tank?" Expect students to explain that inflow and outflow are equal, so the level does not change even though water still moves.
Independent practice (15 min): Students complete the Student Handout, sketching graphs from written descriptions and describing a given graph in words.
Closure and exit ticket (5 min): On an index card, students sketch a tank-level graph for a tank that drains slowly all morning, then is refilled quickly at noon. Collect the cards. If more than a third of the class reverses the rise and fall, reteach the fill-versus-drain distinction next session.
Student Handout
Answer each item about the fictional Marram Dunes pump station tank. No exact numbers are needed; focus on the shape of each graph.
- Sketch a tank-level graph for this day: the tank fills steadily for three hours, holds steady for two hours, then drains steadily for four hours.
- A graph of the tank level rises quickly at first, then keeps rising but more slowly. Describe in words what is happening to the tank.
- On a graph where the line is flat for several hours, what is happening to the tank's water level during that time?
- One tank drains fast and another drains slowly. On a graph, which tank's line is steeper?
- Explain why the tank level often falls in the early evening in a town like Marram Dunes.
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: A graph that rises for the first three hours, stays flat for the next two hours, then falls for the last four hours. The rising and falling parts should look like straight, slanted segments and the middle part should be level.
- Answer: The tank is still filling the whole time, because the line keeps rising, but it is filling more slowly near the end, shown by the line becoming less steep.
- Answer: The water level is staying the same, or constant. Water may still be flowing in and out, but the inflow and the outflow are equal, so the level does not change.
- Answer: The tank that drains fast has the steeper line, because a faster drop in water level over the same time makes a steeper downward slope.
- Answer: In the early evening more people are home using water for cooking, washing, and showers, so the town draws water faster than the pumps refill the tank, and the level falls.
Differentiation
Support
Give students a set of three pre-drawn graph segments (rising, flat, falling) they can arrange and trace to build each graph, rather than drawing freehand. Provide the sentence starters "The tank is filling," "The tank is holding steady," and "The tank is draining" to label each part.
Extension
Ask students to sketch a more complex two-peak day, where the tank fills overnight, drains at a morning rush, refills midday, and drains again at an evening rush, then explain which drain is steeper and why.
ELL supports
Pair each vocabulary word with a hand motion: a rising hand for increasing, a flat hand for constant, and a lowering hand for decreasing. Let students describe their graphs orally using the provided sentence starters before writing.
Extensions
If your local utility shares a public tank-level or demand chart, project it and have students identify the filling, holding, and draining parts on a real graph, connecting the classroom sketches to an actual system.