This is the teacher guide for this lesson. A student-focused guide to assist learners as they perform the activity is available.
Teacher Guide
Meltdown
An exploration of using metal to melt chocolate
How do different metals conduct heat?
This resource was originally published in PhysicsQuest 2011: Spectra Heats Up!
How do different metals conduct heat?
- Hershey's kisses (3)
- 1 steel wire
- 1 copper wire
- 1 aluminum wire
- Hot water
- Cup
- Tape
- Stopwatch/watch with second hand
Students start by discussing what heat does and then they will observe and collect data on the effects of heat on chocolate through different metals. They will end by engaging in a discussion around their conclusions of which metals conducted the heat the most effectively.
Suggested STEP UP Everyday Actions to incorporate into activity
- When pairing students, try to have male/female partners and invite female students to share their ideas first
- As you put students into groups, consider having female or minority students take the leadership role.
- Take note of female participation. If they seem to be taking direction and following along, elevate their voice by asking them a question about their experiment.
- Total time45 - 60 Minutes
- Education levelGrades 5 - 9
- Content AreaThermodynamics
- Educational topicThermodynamics
Metals are generally good at transferring, or conducting, heat. We know not to touch a cookie sheet without a pot holder and that putting a bare hand on your metal car in the winter won’t exactly feel nice. But do all metals conduct the same?
There are really two things going on in this experiment, conduction and melting. Most of us can explain melting without too much difficulty. Melting is when something changes from a solid to a liquid. This happens when there is enough energy, usually in the form of heat, to raise the temperature to the melting point, make the ordered atoms or molecules in the solid become less ordered and move around. At that point it becomes a liquid.
In this experiment conduction in metal moves energy in the form of heat from the hot water up to the chocolate and causes it to melt. Temperature is really a measure of the average kinetic energy in some space, in this case the metal rod. The molecules in the hot water are moving much faster than the molecules in the metal rods. When the fast moving water molecules come in contact with the molecules of the metal they crash into them and transfer some of their energy, making the metal heat up. Then the faster moving metal molecules in the bottom of the metal start jiggling the ones above them and so on right up to the top of the wire and the chocolate. Which gets hot, melts, and slides down the rod to the water. The reason metals conduct heat well is that it is easy for them to get their molecules moving and transfer the energy to other molecules in the metal.
Even though metals as a group are good conductors, some are better conductors than others. One of the places this is easy to see is in cookware. Before the new fancy-dancy pots and pans we have now, most good cookware had copper bottoms. This is because copper is extremely good at conducting heat. Now think of an iron skillet. Unlike other pots, the handle of the skillet is also iron, but we don’t have a problem grabbing it without a pot holder. This is because iron is not a good conductor at all. Important thing to note is that steel is mostly iron.
For this experiment it is okay to assume the steel wire is really an iron wire. This experiment is a really tasty and fun way to show that not all metals conduct equally.
Key terms
These are the key terms that students should know by the END of the two lessons. They do not need to be front loaded. In fact, studies show that presenting key terms to students before the lesson may not be as effective as having students observe and witness the phenomenon the key terms illustrate beforehand and learn the formalized words afterwards. For this reason, we recommend allowing students to grapple with the experiments without knowing these words and then exposing them to the formalized definitions afterwards in the context of what they learned.
However, if these words are helpful for students on an IEP, ELL students, or anyone else that may need more support, please use at your discretion.
- Conduction: Energy in the form of heat moving from one thing to another.
- Kinetic energy: Energy of motion. When things are moving, they have kinetic energy.
- Temperature: Temperature is a measure of how fast the average molecule is moving. It is related to the molecules’ kinetic energy. The faster they move, the higher the kinetic energy and therefore the higher the temperature.
- Melting: The process of changing from a solid to a liquid.
Objectives
Students will collect and interpret data they collect by heating up chocolate kisses.
Before the experiment
- Ask & Discuss
Describe what you think happens when something gets ‘hot’ and ‘heat up’.
- Snowball protocol
- Pair students up
- Give them a minute to think quietly
- Give students 2 minutes to discuss their thinking
- Have students record their answers or share out to the whole group
During the experiment
Collecting data
Make sure students are put into intentional groups. See above.
Students will complete the experiment using the Student Guide where we have outlined the experiment for students and along the way, they record results and answer questions.
Analyzing data
In the student guide, they will add hot water to their experiment and record observations.
Continue to listen in on each group’s discussion, answer as few questions as possible. Even if a group is off a little, they will have a chance to work out these stuck points later.
Teacher tip
A great way to start any physics-related unit is with the STEP UP Careers in Physics lesson. This lesson covers careers one can do with a physics degree, particularly those that help solve societal problems. It helps students assess their personal values in relation to a career in physics, examine profiles of professionals with physics degrees, and envision themselves in a physics career.
Suggested STEP UP Everyday Actions to incorporate into the activity:
- When pairing students, try to have male/female partners and invite female students to share their ideas first.
- As you put students into groups, consider having females or students from underrepresented backgrounds take the leadership role.
- Take note of female participation. If they seem to be only receiving direction and following along, elevate their voice by asking them a question about their experiment.
Consider using whiteboards so students have time to work through their ideas and brainstorm before saying them out loud.
As students experiment, roam around the room to listen in on discussion and notice experiment techniques. If needed, stop the class and call over to a certain group that has hit on an important concept.
Consider using the RIP protocol (Research, Instruct, Plan) for lab group visits and conferring.
Consider culturally responsive tools and strategies and/or open-ended reflection questions to help push student thinking, evidence tracking, and connections to their lives.
Conclusion
Share-Trade protocol to have students share and refine their thinking.
- Each student writes their individual thoughts to the question: Did all the kisses melt and slide down the wires? If not, why do you think they didn’t?
- Students stand up with their ideas on paper and move around the room.
- Each student finds someone they don’t know very well and forms a partnership with them. To form a partnership, students must high five.
- With their partners, students share their ideas and trade papers.
- Each student is now responsible for sharing the ideas of the person they just spoke with, even if they don’t agree with those ideas. This isn’t a time for them to critique their partners’ ideas.
- Students form partnerships three or four times so they see and explain multiple ideas.
- Students return to their seats and write a final explanation or idea.
After students have had a chance to discuss key ideas from the lesson and complete their student guides, you can now clarify and give concise definitions to the forces they experimented with.
Real world connections -
- Using what you learned about conduction, explain how a grill can be used to cook your food.
Suggestions for drawing, illustrating, presenting content in creative ways
- Have students illustrate the movement of particles at different temperatures to represent kinetic energy (higher temperature=faster moving molecules)
Engineering and design challenges connected to the content
- Watch this video about how salt is used to help melt ice in the winter. Design a way to use melting or freezing to solve another problem.
- MS-PS4-3Integrate qualitative scientific and technical information to support the claim that digitized signals are a more reliable way to encode and transmit information than analog signals.
- MS-PS4-1Use mathematical representations to describe a simple model for waves that includes how the amplitude of a wave is related to the energy in a wave.
Credits
Written by Rebecca Thompson
Illustrations by Kerry G. Johnson
Activity illustrations by Nancy Bennett-Karasik
Updated in 2023 by Sierra Crandell, M.Ed. partially funded by Eucalyptus Foundation
Extension by Jenna Tempkin with Society of Physics Students (SPS)