Design Challenge: A Battery Warmer for a Trail Camera

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Design Challenge: A Battery Warmer for a Trail Camera

Use test data to choose a chemical process and a box that keep a battery warm all night.

Test 1: Three chemical warmers

Read the passage and study Table 1. Then answer the questions.

Cold Nights, Dead Batteries

1Every winter, a nature group in Cedar Falls straps trail cameras to trees to photograph foxes, deer and owls at night. On cold nights, many of the cameras quit after a few hours, because their batteries deliver much less power when they are cold. The group asked the teen club at the Cedar Falls Community Makerspace for help. Club members Paz Echeverría and Finn Gallagher, both seventh graders, decided to build a battery warmer: a small foam box around the battery pack, warmed by a chemical process. Their mentor, Ms. Oksana Petrenko, is an electrical engineer who volunteers at the makerspace.

2The team agreed on four criteria with the nature group. The battery must stay at or above 10 °C for at least 6 hours, the length of a camera's night shift. It must never go above 40 °C, which can damage the battery. No liquid may be inside the box, because the battery pack and its wires sit there. The chemicals must cost less than $0.75 per night.

3For Test 1, the team built four identical boxes with 2 cm foam walls and a few small air holes. In each box, a 60 g aluminum block stood in for the battery pack, with a temperature probe taped to it. The boxes, blocks and all the warmers were left overnight in an unheated shed at 2 °C, so everything started at the same temperature. Then Finn started each warmer, set it against its block and closed the box. One box got no warmer.

4The iron warmer was a cloth pouch holding 40 g of iron powder mixed with salt and damp vermiculite. When its plastic wrapper was opened, air reached the iron, and a reddish-brown solid slowly formed. The calcium chloride warmer was a sealed plastic pouch with 30 g of calcium chloride and an inner bag of 100 mL of water; squeezing it broke the inner bag, and the salt dissolved. The third pouch held 20 g of baking soda and an inner bag of 100 mL of vinegar, with a small vent; when squeezed, it fizzed and swelled with gas.

Table 1. Block Temperature in Each Box, Shed at 2 °C (°C)
Time (h)	No warmer	Iron pouch	Calcium chloride	Baking soda + vinegar
0	2	2	2	2
0.5	2	15	29	0
1	2	22	23	1
2	2	25	13	2
4	2	24	5	2
6	2	19	3	2
8	2	12	2	2
10	2	4	2	2

1.

Use Table 1.

In the first half hour, the calcium chloride pouch warmed its block by °C.

2.

Which result is the best evidence that the baking soda and vinegar process absorbed thermal energy?

A. Its pouch fizzed and swelled with gas when Finn squeezed it.B. Its block fell to 0 °C while the no-warmer block stayed at 2 °C.C. Its pouch cost less than the other two chemical pouches.D. Its block was back at 2 °C by the 2-hour reading.

3.

Use the criteria in paragraph 2 and Table 1. Match each box in Test 1 to the result that describes it.

4.

The calcium chloride pouch warmed its block faster than the iron pouch did, but the iron pouch kept its block warm much longer. Which explanation fits paragraph 4 and Table 1 best?

A. The water in the calcium chloride pouch froze after 2 hours and stopped the dissolving.B. The iron pouch was heavier, so it held more heat from the shed before the test began.C. The salt dissolved quickly and released its energy early; the iron reacted slowly for hours.D. The calcium chloride stored cold at first and let it out slowly after the first hour.

Test 2: How thick a box?

Read the paragraph and study Table 2. Use the criteria in paragraph 2 to answer.

For Test 2, the team used a 40 g iron pouch every time and changed only the thickness of the foam walls. Each box ran in the same 2 °C shed with the same 60 g block and probe. Table 2 comes from the probe's full minute-by-minute record.

Table 2. 40 g Iron Pouch in Three Boxes (shed at 2 °C)
Foam wall (cm)	Highest block temp (°C)	Hours at or above 10 °C
1	17	5
2	25	8
4	41	12

5.

Use Table 2.

The block in the 4 cm box stayed at or above 10 °C for hours longer than the block in the 1 cm box.

6.

Each box held the same 40 g iron pouch. Why did the thicker walls keep the block warmer for longer?

A. The thicker foam made the iron release more thermal energy in total.B. The thicker foam kept the shed's cold from flowing into the box.C. The thicker foam trapped extra oxygen, so the iron reacted faster.D. The thicker foam slowed the flow of thermal energy out to the shed.

7.

Which design in Table 2 meets both temperature criteria in paragraph 2?

A. The 1 cm box, because its block never got close to 40 °CB. The 2 cm box, because its block stayed between 10 °C and 40 °C for 8 hoursC. The 4 cm box, because its block stayed at or above 10 °C for 12 hours

8.

Paz wonders whether a smaller 20 g iron pouch in the 4 cm box would meet every criterion for less money. Which plan is a fair test of her idea?

A. Run a 20 g pouch in a 4 cm box in the 2 °C shed with the same block and probe, three times.B. Run a 20 g pouch in a 4 cm box outdoors on a mild 10 °C night, then compare it with Table 2.C. Run a 20 g pouch in a 4 cm box with a lighter 30 g block, so the block warms up faster.D. Run a 20 g pouch in a 4 cm box and a 60 g pouch in a 1 cm box, then compare the two.

9.

Suppose a camera is set up on a much colder night, at −10 °C, with the 40 g pouch in the 2 cm box. What would most likely happen?

A. The block would stay at or above 10 °C for fewer than 8 hours, because energy would leave the box faster.B. The block would stay at or above 10 °C for about 8 hours, because the pouch holds the same 40 g of iron.C. The block would get warmer than 25 °C, because a colder night makes the iron release more energy.D. The block would stay near −10 °C, because iron powder does not react with oxygen below 0 °C.

Make the case

Use both tables, the criteria and what you know about thermal energy.

10.

Finn says, “The calcium chloride pouch is the best warmer, because it heated the block the fastest. A faster warmer always releases more energy.” Do you agree? Write a claim, use evidence from Table 1 and the criteria, and explain where the thermal energy comes from and why the iron pouch worked better for a camera.