Testing Sleeping Pads for a Night on the Snow

Test and improve a pad that slows energy transfer into the snow.

Answer Key

Round 1: Five pads

Read the passage and Table 1, then answer questions 1–4.

Cold From Below

1Every February, the outdoor club at Juniper Hill Middle School camps for one night in tents on a snowy meadow. Last year several campers woke up shivering, even inside warm sleeping bags. Their leader, Ms. Coralie Duchamp, said the problem was probably under them, not around them. A sleeping bag gets squashed flat where a camper lies on it, and the snow below stays well below freezing all night.

2Club member Jaspreet Gill decided to test sleeping pads before this year's trip. A camper is warmer than the snow, so she needed a model of a warm body. Ms. Duchamp filled identical 1 L bottles with water at 40 °C and slid each one into the same kind of fleece sleeve. Each bottle lay on a different pad, side by side on packed snow inside a tent. The snow was about −8 °C and the air in the tent about −6 °C. After 2 hours, Jaspreet measured the water temperature in each bottle.

3The club set two requirements. A pad must keep the water at 22 °C or warmer after 2 hours, and it must have a mass of no more than 600 g, because each camper carries a pad in a backpack.

4Pad D, an air pad, has wide chambers filled only with air. The foam pads are made of tiny closed bubbles of air inside the foam. In Round 2, the club tried to improve Pad D, because it rolls up smaller than the foam pads. They added a thin, shiny foil sheet inside it, a layer of fluffy fiber fill that packs the chambers, or both.

Table 1: Round 1 (every bottle starts at 40 °C)
Pad	Build	Mass (g)	Water after 2 h (°C)
A	No pad (thin tarp only)	0	12
B	Foam, 1 cm	250	19
C	Foam, 2 cm	480	24
D	Air pad, 6 cm	450	18
E	Foam 2 cm on top of air pad	930	28

Use Table 1.

The water on the thin tarp (Pad A) cooled by 28 °C in 2 hours. The water on Pad C cooled by 16 °C.

Which statement best describes the energy transfer for the bottle on Pad B?

A. Energy moved into the tent air instead, because the foam kept the bottle from touching the snow.
B. Cold moved up from the snow into the bottle, and the foam let some of the cold through.
C. Thermal energy moved from the warm water toward the snow, and the foam slowed that transfer.
D. The foam gave the water extra thermal energy, so the water ended warmer than on Pad A.

Use paragraph 4. Pad D is 6 cm thick, yet the water on it ended colder than on the 1 cm foam pad. Which is the best explanation?

A. The thick air pad lifted the bottle into the colder tent air, which took energy from the bottle.
B. The air pad has more mass than the 1 cm foam pad, so it held more of the snow's cold inside it.
C. Air lets energy pass through it much faster than solid foam, so the air pad lost energy faster.
D. Air in the wide chambers can flow and carry energy downward, while foam traps air in tiny bubbles.

Pad E kept the water warmest of all the Round 1 pads. Why is it still not a good choice for the trip?

A. Its mass is 930 g, which is more than the 600 g each camper can carry for a pad.
B. Its water ended below 22 °C, because the air pad under the foam let energy escape.
C. It was tested last, so the snow under it had already warmed up from the other pads.
D. It kept the water so warm that the bottle would be too hot for a camper to lie on.

Round 2: Improving the air pad

Use Table 2, Table 1 and paragraph 4 to answer questions 5–8. Round 2 was run the same way as Round 1, on a night with the same snow and air temperatures.

Table 2: Round 2 (every bottle starts at 40 °C)
Pad	Change to Pad D	Mass (g)	Water after 2 h (°C)
D	None	450	18
D1	Foil sheet inside	480	21
D2	Fiber fill inside	530	24
D3	Foil sheet and fiber fill	570	27

Use Table 2.

Adding both the foil sheet and the fiber fill kept the water 9 °C warmer than on the plain air pad, for an extra 120 g of mass.

Pad D2 kept the water 6 °C warmer than Pad D. Which explanation fits paragraph 4 and the data best?

A. The fiber fill made the pad heavier, and heavier pads hold the bottle farther from the snow.
B. The fiber fill packed the chambers, so the air inside could not flow and carry energy away.
C. The fiber fill soaked up cold from the snow, so less of the cold reached the bottle above it.
D. The fiber fill gave off thermal energy of its own during the night and warmed the water.

Use paragraph 3 and both tables. Circle each pad that meets both of the club's requirements.

Pad BPad CPad DPad EPad D1Pad D2Pad D3

A week later, Jaspreet tested Pad D1 again on a night when the tent air was −1 °C. The water ended at 25 °C. She says, "Now D1 works better than D2." What is the main problem with her conclusion?

A. Pad D1 has a foil sheet, and foil works better on warm nights because it absorbs the warmth.
B. The warmer night made a smaller temperature difference, so the water lost less energy on any pad.
C. She used the same bottle and fleece sleeve as before, so the water started at 40 °C again.
D. She should have measured the water after 1 hour instead, since the bottle cools fastest then.

Explain the design

Use everything on the page to answer questions 9–11.

Complete Jaspreet's summary of Pad D3. Use words from the word bank. Two words are not used.

Word bank: warmer · colder · slows · speeds · reflects · flowing · cold

Thermal energy moves from the warmer camper toward the colder snow. The foil sheet reflects some of the energy given off by the body back up. The fiber fill keeps the air in the chambers from flowing. Each part slows the transfer of energy into the snow.

10.

In June, the club will camp on a hot beach. They want to keep a bag of ice from melting on the warm sand during an afternoon. Based on both tables, which pad would most likely keep the most ice frozen?

A. Pad D3, because it slowed energy transfer more than Pads A, B and D, from either side
B. Pad D, because the moving air in its wide chambers would carry the warmth away
C. Pad B, because thin foam lets energy from the sand reach the ice more slowly than thick foam
D. Pad A, because the thin tarp lets the cold of the ice spread out into the sand

11.

After Round 1, a club member said, "Air pads are cold because air lets energy pass through it easily. We should give up on air pads and only buy foam." Do you agree? Write a claim, give evidence from both tables and paragraph 4, and explain your reasoning about thermal energy transfer.

I disagree. In Round 1 the plain air pad (D) kept the water at only 18 °C, but in Round 2 the same air pad with fiber fill (D2) kept it at 24 °C, and with fiber fill and a foil sheet (D3) at 27 °C, which is warmer than the 2 cm foam pad's 24 °C. D3 also has a mass of 570 g, under the 600 g limit. So the air was not the problem. In the plain pad, the air could flow around the wide chambers and carry energy from the warm side down to the cold snow. When the fiber fill stopped the air from flowing, and the foil reflected energy back up, the pad slowed the transfer of thermal energy into the snow. The club could choose an improved air pad, not only foam.