Directions for teachers:
This discussion exercise is based on the Science News article “Humans may not be able to handle as much heat as scientists thought.” After students have read the article, use the first set of questions to have students reflect on a time they experienced heat and encourage them to draw similarities among their answers. Then use the second set of questions to lead a discussion about the physics of heat. Finally, students will apply what they learned by drawing diagrams.
Coming in hot
1. Think of a time when you were excessively hot. Where were you and what were you doing? What were the weather conditions?
Student answers will vary. During the discussion get students to focus on the weather conditions, in particular the temperature and perceived humidity. Ask students to think about the heat and conditions on their body when it was at rest.
2. What did you notice about your body? How did you feel physically and mentally?
Student answers will vary but they will likely mention sweating and an increase in skin temperature and redness. They may also mention feeling irritable and having less patience than normal.
3. What did you do to cool down? How long did it take for you to be comfortable again?
Student answers will vary. If answers involve moving to another location, ask students to define how the weather conditions are similar or different than those in the old environment. Ask students to think about why people may require different lengths of time to cool off.
The science of heat
1. What is a system? What are two systems that interact in the Science News article?
A system is a network of parts that together work to achieve some function. Two systems in the article that interact are the human body and the weather or environment.
2. What is thermal energy? What is heat? How are they related?
Thermal energy is a form of energy produced by vibrating atoms and molecules within a system. Heat is the flow of thermal energy from one system to another.
3. If two systems at different temperatures are brought together, in what direction will heat energy flow? For example, if hot coffee is poured into a room temperature mug, will heat energy flow from the coffee to the mug or from the mug to the coffee? Explain why.
As the coffee meets the mug, energy will flow from the coffee to the mug. That’s because atoms in warm systems have more kinetic energy than atoms in cold systems. The high-energy atoms of the coffee will collide with the low-energy atoms of the mug, transferring heat energy to the mug’s atoms until the systems reach equilibrium.
4. What will happen to the temperature of the coffee (the warmer system) over time? What about the mug (the cooler system)?
Since energy is transferred from the warmer system to the cooler system, generally the temperature of the warmer system will go down and the cooler system will go up until they reach equilibrium.
5. Does a change in temperature always occur when heat energy flows in or out of a system? Explain.
No. For instance, a cool system may absorb energy from a warm system without experiencing a rise in temperature if that energy changed the physical state of matter in the cool system.
6. What is evaporation and how does it involve heat? Explain.
Evaporation is a process by which liquid matter transforms into gas. During the process, the liquid absorbs heat energy, which separates molecules in the liquid and thus transforms it into a gas. Since evaporation involves the absorption of heat energy, it is called an endothermic process.
1. How does sweating cool the body? Diagram the process.
Sweating cools our bodies through evaporation. Excess body heat converts beads of sweat into gas, which cools us down. Student diagrams will vary, but all should define two systems: the human body and the beads of liquid sweat on the surface of the skin. Generally, diagrams will show excess heat energy from the human body turning liquid sweat on the skin into a gas, thus cooling the body. As an optional extension, have students diagram the process under hot and dry weather conditions as well as hot and humid conditions.
2. Brainstorm at least two examples of technology that help cool the human body. Explain why the technologies work.
Student answers will vary but may include air conditioning, fans, swamp coolers or other devices that lower external air temperatures or circulate air in a way that increases evaporation from the skin.