Surface Area and Evaporation: A Science Fair Investigation

Testable question: Does the surface area of a container's opening change how fast water evaporates? Every container in this test starts with the same volume of water.

Write a hypothesis. A hypothesis is a prediction you can test. Fill in this sentence before you collect any data:

"If a container has a larger opening, then it will lose water (faster / slower / at the same rate) than a container with a smaller opening, because ___."

Write your reason in the blank before Day 0. Do not change your hypothesis once the test starts.

Why surface area might matter. Evaporation happens at the top of the water. Water molecules there can gain enough energy to break free. They escape into the air as vapor. Molecules deeper in the container cannot escape this way. A wider opening puts more molecules next to the air at once. More molecules can escape each hour. This happens even though every container starts with the same volume.

Variables in this investigation.

Materials, per team.

• 3 straight-sided containers with different opening sizes: Container A (smallest opening), Container B (medium opening), Container C (largest opening). Example set: a tall glass, a wide-mouth jar, a shallow pan.
• Straight sides only. A narrow-necked bottle changes shape at different fill heights, so its water surface would not match its opening.
• 900 mL of water total: 300 mL for each container. A measuring cup or graduated cylinder for pouring.
• 1 digital kitchen or gram scale for the mass method, OR 1 ruler plus a thin straw or dowel as a dipstick for the depth method.
• 1 sheet of 1 cm grid paper, for tracing each container's opening.
• Masking tape and a permanent marker, for labeling A, B, and C.
• 1 data log sheet (template below) and a pencil.
• A shared spot, such as a windowsill or shelf, away from vents, drafts, and direct sun. The containers stay here, undisturbed, for two weeks.
• Graph paper or graphing software, for the final graphs.
• Poster board or a tri-fold display board, for the final presentation.

Data log template. Copy this table onto the data log sheet. Record one row per day, using mass in grams or depth in millimeters, matching the method the team picked before Day 0. One milliliter of water weighs about one gram, so a team using the mass method can weigh each container empty, subtract that mass from its Day 0 reading, and check the result against the starting volume that was poured.

Fair-testing guidance. Every team must measure the same way every time.

• Pick one method, mass or depth, before Day 0. Use only that method for the whole test.
• Keep all three containers in one location for the full two weeks. Moving even one container to a sunnier or draftier spot changes its rate for a reason that has nothing to do with surface area.
• Take every measurement at the same time each day.
• Pour the exact same volume into every container. Use the same measuring cup each time.
• Write down anything unusual, such as an open window or a running heater, in the notes column. A stray draft is the most common reason results come out mixed.

Final deliverable. Each team turns in one completed data log, two labeled graphs (built in Milestone 4), and a written conclusion (Milestone 5). These go on a poster or in a short report for a class science fair presentation.

This project runs for ten school days, about two school weeks. It combines five formal class sessions with a short daily measurement on the other school days.

Daily measurement routine (other school days, about 2 to 3 minutes each). Two data recorders from each team measure that day's reading for Containers A, B, and C. They use the team's chosen method, at the same time of day used on Day 0. They add the reading to the shared data log before the next class period.

1. Session 1 — Day 0, about 45 minutes. The class discusses evaporation and the testable question. Each team writes its hypothesis. Teams trace each container's opening onto grid paper and count the squares to estimate its surface area in square centimeters. Teams record all three estimates on the data log. Teams pour the same volume into all three containers, take the Day 0 reading, and set the containers in the shared spot. Output: a written hypothesis, three surface-area estimates, and a Day 0 reading for every team.

2. Session 2 — Day 4, about 30 minutes. Teams review four days of data. They check for a missed reading or a number that looks like a mistake. Using the data from Day 0 through Day 4, each team finds a running total of water lost per container. Each team also finds an early average rate: total lost divided by the number of calendar days so far, counting weekend days. Depth-method teams first turn each depth drop into volume: the depth lost in centimeters (millimeters divided by 10) times the container's surface area in square centimeters gives milliliters lost, about the same number of grams. Every container loses about the same depth each day, so only the volume shows whether the opening size matters. Output: a data log through Day 4, with a first rate calculation for each container.

3. Session 3 — Day 9, about 30 minutes. Teams take the tenth and final reading. Teams then calculate two numbers per container: the total water lost across all ten days, and the average daily rate. Depth-method teams use volume lost, found the same way as in Session 2. The daily rate is the total water lost divided by the number of calendar days from the Day 0 date to the Day 9 date. Count the weekend days too, since water keeps evaporating, and use the Date column to count. Output: a completed data log and a finished table of totals and daily rates for Containers A, B, and C.

4. Session 4 — the next class period, about 45 minutes. Teams build two graphs from their finished data. Graph 1 plots water lost on the vertical axis against calendar days since Day 0 on the horizontal axis, found from the Date column. It has one line for each of the three containers, on the same axes. Graph 2 plots each container's average daily rate on the vertical axis against its surface area on the horizontal axis. Graph 2 has three points, one per container. Graph 2 tests the hypothesis most directly. Output: two completed, labeled graphs.

5. Session 5 — the class period after that, about 50 minutes. Teams write a conclusion and build their presentation.

   Presentation guidance.

   • Photograph the three containers side by side on Day 0 and again on Day 9. A visible difference in the remaining water is often the clearest evidence a viewer can see at a glance.
   • Show the completed data log and both graphs from Session 4 on the poster or in the report.
   • State the conclusion in three honest parts: what the hypothesis predicted, what the data showed, and whether the two match.
   • If the data supports the hypothesis, explain how Graph 2 shows the pattern, container by container.
   • If the data does not support the hypothesis, say so directly. For example, the rates might come out nearly equal, or a smaller opening might show the fastest rate. Give one specific, real reason this can happen: a draft that reached one container and not the others, a reading taken at a different time on one day, or ten days simply being too short for the true difference to show. A result that does not match the hypothesis is still a real finding and belongs in the report.
   • Close with one or two sentences that connect the result back to the reservoirs and storage tanks described in the Overview.

   Output: a completed presentation, with the data log, both graphs, and a written conclusion, ready to share with the class.