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Lesson plan Grade 7 Art & Music

Saltwick Bay Desalination Cutaway: A Reverse Osmosis Art Lesson

A grade 7 art lesson where students draw a scale cutaway poster of one reverse osmosis vessel for a fictional seawater desalination plant.

Objectives

  1. Students will draw a reverse osmosis vessel to a stated scale on grid paper.
  2. Students will compute actual lengths from a scale drawing using the scale factor.
  3. Students will explain how a reverse osmosis membrane separates salt from seawater.

Vocabulary

Reverse osmosis
Reverse osmosis cleans water by pushing it through a membrane with holes so tiny that salt and most other dissolved things cannot fit through. It can even turn seawater into fresh water.
Brine
The extra-salty water left over after desalination pulls fresh water out of seawater. Plants must dispose of it carefully so it does not harm sea life.

Also: membrane, cross-section, scale

Teacher overview

A reverse osmosis plant pushes seawater against a thin membrane at high pressure. Fresh water passes through, while the leftover salty water, called brine, is sent back out. This lesson turns that hidden process into a labeled cutaway poster, the kind a plant hangs in its lobby to show visitors how the equipment works. Students design the poster for the fictional Saltwick Bay desalination plant, drawing one pressure vessel to scale so the parts stay in correct proportion. A common misconception this lesson addresses is that the parts of a cutaway can be drawn at any size and still be accurate; without a consistent scale, the pump ends up larger than the vessel and the poster misleads the viewer.

Procedure

Hook (10 min): Show two quick sketches of the same machine you draw on the board: one where the parts are in proportion and one where they are not. Ask students which sketch a plant should hang for visitors, and why proportion matters in a technical drawing.

Direct instruction (15 min): Explain reverse osmosis in plain terms: pressure forces seawater against a membrane, fresh water crosses, and brine is rejected. Then model scale drawing with a teacher example that is different from the student handout. Suppose a filter housing is 12 feet long and the poster uses a scale of 1 inch equals 3 feet. Show that 12 divided by 3 gives a 4-inch line on the paper. Draw and label it so students see the method before they try their own numbers.

Guided practice (15 min): Hand out the dimension sheet for the Saltwick Bay vessel. Working from the handout, students set up their grid paper, mark the scale, and begin the vessel outline. Circulate and check that each student converts feet to inches with the stated scale rather than guessing a size.

Independent practice (15 min): Students finish the cutaway, label the membrane, feed pipe, clean-water pipe, and brine outlet, and complete the handout questions in order.

Closure / exit ticket (5 min): On an index card, students answer one check question: at a scale of 1 inch equals 2 feet, how long is the drawing of a 14-foot vessel? Collect and scan the cards; if more than three students miss the division, reteach the scale step before the next session.

Saltwick Bay Desalination Cutaway: A Reverse Osmosis Art Lesson — Grade 7 Art & Music
Name: ____________________________ Date: ______________

Student Handout

Suppose the fictional Saltwick Bay desalination plant asks you to draw a cutaway poster of one pressure vessel. Use a scale of 1 inch equals 2 feet for questions 1 through 4. The real measurements are listed below.

  • The pressure vessel is 20 feet long.
  • The feed pump next to it is 3 feet wide.
  • The brine outlet pipe is 6 feet long.
  1. At 1 inch equals 2 feet, how long should the 20-foot vessel be in your drawing?
  2. How wide should the 3-foot feed pump be in your drawing at the same scale?
  3. How long should the 6-foot brine outlet pipe be in your drawing?
  4. Your drawing shows the clean-water pipe as 2 inches long. How long is the real pipe?
  5. A partner draws the same 20-foot vessel as a 5-inch line. What scale did the partner use, written as 1 inch equals how many feet?
  6. Redraw the 3-foot feed pump at the partner's new scale from question 5. How wide is it now?

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: 10 inches.
    20 feet divided by 2 feet per inch equals a 10-inch line on the paper.
  2. Answer: 1.5 inches.
    3 feet divided by 2 feet per inch equals 1.5 inches.
  3. Answer: 3 inches.
    6 feet divided by 2 feet per inch equals 3 inches.
  4. Answer: 4 feet.
    2 inches times 2 feet per inch equals 4 feet of real pipe.
  5. Answer: 1 inch equals 4 feet.
    20 real feet drawn as 5 inches means each inch stands for 20 divided by 5, which is 4 feet.
  6. Answer: 0.75 inch.
    At 1 inch equals 4 feet, the 3-foot pump is 3 divided by 4, which is 0.75 inch.

Differentiation

Support

Give these students grid paper already marked with the scale and one part drawn in, so they convert and add only the remaining parts. Provide the division for questions 1 through 3 set up as blanks they finish.

Extension

Ask students to add a second vessel to the poster at half the drawing size, choosing a new scale that makes the whole set fit one page, and to write the new scale as a ratio in lowest terms.

ELL supports

Pre-teach "membrane," "brine," "cross-section," and "scale" with a simple labeled sketch and a translation where possible. Allow labels on the poster to be single words or short phrases rather than full sentences.