# Build a Thermos

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## Objective

SWBAT will be able to design, construct, and test a thermos structure to determine which model keeps the warmest temperature.

#### Big Idea

Need STEM lessons to help your students explore heat and temperature? This is the one.

## Getting Started

Prerequisites

This lesson is designed to be used within the heat transfer unit as an engineering exploration of the property.

Goals

My goal is to teach students:

• The difference in heat conductivity of different materials.
• What the atomic principle of heat transfer is (molecules hit into each other and slow down/move faster).
• Engage students in thinking about the principles of engineering (designing to meet criteria determined by the desired result).

Total class time

150 minutes (3 class periods, 1 period for demo, in-class design, 1 period for student-requested informational experiments, 1 period for final experiment/explanation).

First period Prep

Finish this prep at least 45 minutes before the class period in which this lab will be run (several hours should be fine/demonstrate the point.)

For the prep, prepare at least 0.75 L of boiling water.  Then pour 250 mL each into a vacuum thermos, a metal cup/ water bottle, and a metal coffee cup.  Make a note of the temperature and the time, and set aside for at least 45 minutes.

First and Second Period

At the beginning of the lab, tell the students using any setup you wish.  I’ll talk about making tea before I leave home, and wanting to keep it warm so I can drink it later in the day, so which cup do they think I should use?  Get a poll from the class, then measure the temperatures.  It should be (from high to low) Thermos, metal coffee cup, metal.  Ask them why they think it is, they are all metal, right?  Let them propose a few ideas, then give them the assignment to design and build the cup that can keep coffee the warmest the longest (with a prize going to the winner).  Rules are attached.  Give them until the next day to complete their schematic, and approve or suggest modifications, and allow them a week to build the materials.  Give them

Third Period

Prepare lots of boiling water, and a classroom control of the thermos, metal cup, insulated coffee cup, plastic cup, glass, and ceramic cup.  Take the temperatures with 15 minutes left in class for all samples and have the students do it for their own sample.  During the period, each student gives a 3-5 minute presentation about their design, and how they thought it would work, why they thought it was the best way to do this.

At the end of class explain to the students how a thermos works (vacuum) and ask them why that is so bad at transferring heat, then explain why that works, and a couple of other strategies for a good insulator (multiple buffered layers of air.)

## Define the Problem

10 minutes

On first first day of this project I'll talk about making tea before I leave home, and wanting to keep it warm so I can drink it later in the day, and ask students which cup do they think I should use (Thermos, metal coffee cup, ceramic)

Get a poll from the class, then measure the temperatures.  It should be (from high to low) Thermos, metal coffee cup, ceramic.

Ask them why they think this was so. Let them propose a few ideas then give them the design problem.

Design and build a thermos/cup that can keep 250 ml of water the warmest for 30 minutes.

Give students until the next day to complete their schematic, and approve or suggest modifications, and allow them a week to build the materials.

Constraints:

1. Must fit in your teacher’s hand.
2. Must hold 250 mL of hot water.
3. Be structurally sound (doesn't easily fall apart).
4. No part of your container may be permanently altered as a result of the final test (your results must be repeatable without changing your container.)

You May:

• Use a plastic/glass/ceramic cup as the core
• Use any materials at home or from the store as long as they obey the “May NOT” section.

You May NOT:

• Use a thermos/travel mug as the core
• Use materials only accessible to research laboratory personnel

You must submit a detailed blueprint to your teacher and be approved before beginning construction

One class period will be allowed for students to run preliminary tests to aid their design questions.  All tests must be proposed and approved before be attempted.

Grades are based on:

• Blueprint
• Preliminary tests
• Novelty of design (the method used to keep the water hot)
• Efficiency of design (how much material used per ºC, weight, width)
• Execution of design (how well your idea translated from your blueprint plans)
• Flair

## Explore

After going over the design challenge I give students a design workbook that includes each step of the engineering design process to be completed. If this is your first time teaching an engineering project, you may want to complete this activity on your own first to get a feel for what is involved.

Be sure to set three dates for the project. The preliminary test date, the final test date and the day that their summaries are due. I like to spread these out by about 3-4 class periods.

For the preliminary test, students should have their initial thermos ready to be tested. You will want to prepare beakers of hot water on hot plates that are all at the same starting temp. 85-90 C is sufficient.

Have plenty of thermometers on hand that are calibrated and comparable.

Fill each cup with 250 ml of hot water and measure the temperature for 30 minutes. Report out the results and have students reflect on how their thermos performed.

I like to have students share out their data with the class.

Time permitting this may be a good time to talk about redesign. If you are short on time, make sure to run the discussion on the next day.

Remind students of the date of the final test (2-3 days later) repeatedly. In between this time they should:

1. Revisit their initial designs
2. Make any changes or adjustments
3. Draw up new plan or modify the old ones if necessary
4. Bring in their completed thermoses on the final test date.

## Explain

30 minutes

When testing is complete we will discuss the following:

• Why did some thermoses fall short of our expectations?
• What design features were correlated to the functions?
• What about the differences in design?
• Which thermos was worked the best?  Why?
• What changes are you thinking about trying and why?

Give them time to redesign and rebuild asking them to record their work in the workbook or a journal. Remind them of the final test date.

## Evaluate

50 minutes

Once all of the testing is complete I ask each student to team of students to write up a summary and provide them with a rubric. I ask them to turn these in 3-4 days after the final test date.