Thermal expansion model
1. Discuss climate change and sea-level rise with students. Ask students to identify causes of sea-level rise. If students do not mention thermal expansion, explain that in addition to ice melt, there is another phenomenon that contributes to sea-level rise. The following activity will demonstrate that phenomenon.
2. Depending on students’ age and ability, have them cut a straw-size hole in the cap of their water bottle. If done while the cap is still attached to the bottle, students will have more area to grab and can keep their fingers farther from the cutting device.
3. Have students insert the straw into the hole. The straw should extend down approximately 2-3 inches into the bottle when the cap is on. (During this step, students can keep the bottle and cap separate.) Using hot glue, putty or another sealant, close any gaps around the straw. As the glue dries, students should be sure the straw is as close to perpendicular to the top of the lid as possible.
4. Have students add several drops of food coloring to the water bottle, fill the bottle with water completely to the rim, then top with the straw and cap assembly and tighten. Some overflow when the cap is attached is ok. The water in the straw should be above the cap, but low enough to allow measurements of changes.
5. Students need to mark the straw to indicate the base, or zero, level of the water. Because moving and squeezing the bottle can change its shape, internal volume and water level, once the line is marked, avoid moving or handling the bottle while the water is warming.
6. Have students direct a heat source at the bottle. Consider making and testing it in advance to get an idea of how long it may take.
7. At consistent intervals, students should measure and record the water level compared with the “zero level”, in millimeters, and make note of what’s happening. If using thermometers, students should also record the temperature at these intervals.
8. Ask students to describe what they observed in the straw. Students should notice the water level is rising as heat is added to the water. Explain to students that this phenomenon, mentioned in Step 1, is known as thermal expansion.
Evaluation
Ask students to observe the data and discuss the following questions:
What happened to the water level as heat energy was added?
Answer: The water level rose as the temperature increased.
Explain why the water level in the straw changed over time. What caused this?
Answer: Water increases in volume when heated. The added energy that came in the form of heat caused the water molecules to move around more. As they moved and bounced off of each other, they took up more space, thereby increasing in volume. As the temperature of the water in the bottle increased, the volume of water in the bottle increased (expanded). This process is called thermal expansion.
Ask students to identify causes of sea-level rise with sufficient detail to demonstrate understanding: the ocean’s heat capacity allows it to absorb a lot of energy in the form of heat as land and air temperatures rise. Thermal expansion increases the volume that ocean water takes up, leading to sea-level rise.