A Cold Frame for Frosty Spring Nights

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A Cold Frame for Frosty Spring Nights

Test cold frame designs that protect seedlings from frost and afternoon heat.

Part 1: Five frames, one day and one night

Read the passage and both tables. Use them to answer questions 1–6.

Frost Warnings in April

1Every April, the Maple Street Community Workshop helps neighbors start vegetable gardens. Pepper and tomato seedlings are ready to go outside early in the spring, but in this town the air on a clear night can still drop below freezing, and frost can kill young leaves. Ayasha Bergström, a sixth grader who builds things at the workshop on weekends, decided to design a cold frame: a low wooden box with a clear lid that sits over the seedlings like a small greenhouse.

2Her mentor, Lionel Achebe, helped her write three requirements. First, on a clear night when the outside air falls to −3 °C, the air inside the frame must stay at 2 °C or warmer. Second, on a sunny afternoon with the lid closed, the air inside must stay at 35 °C or cooler, because too much heat can also harm seedlings. Third, the materials for one frame must cost $40 or less.

3Ayasha built five frames of the same size from the same plywood and set them side by side in a sunny corner of the workshop yard. Frame A had a single sheet of clear plastic as its lid. Frame B had a double lid: two sheets of clear plastic with a 2 cm air gap between them. Frames C, D and E also held 4 L plastic jugs of water painted flat black, set along the back wall where the sunlight hit them. A small temperature logger inside each frame recorded the air temperature every hour through one sunny day and the clear night that followed.

4During the afternoon, the black jugs felt warm to the touch. At sunrise they felt cooler than they had at sunset, but still warmer than the frosty air outside. Ayasha's price list showed that a second plastic sheet for a double lid costs $8, and each set of four jugs with paint costs $6.

Table 1: Frame Tests (outside air: 14 °C in the afternoon, −3 °C at night)
Frame	Lid	Black water jugs	Afternoon high (°C)	Night low (°C)	Cost
A	Single	0	38	−1	$22
B	Double	0	44	1	$30
C	Single	4	31	3	$28
D	Double	4	33	5	$36
E	Double	8	29	7	$42

Table 2: Overnight Log for Frames A and D (air temperature, °C)
Time	Outside air	Frame A	Frame D	Jug surface in D
6 PM	8	12	16	24
10 PM	2	4	12	17
2 AM	−1	1	8	12
6 AM	−3	−1	5	8

1.

Use Table 1.

How many degrees warmer was the night low in Frame D than in Frame A? °C

2.

Use paragraph 2 and Table 1. Circle each frame that meets all three of Ayasha's requirements.

3.

Frames A and B differ only in the lid. Frame B was warmer at night and also hotter in the afternoon. Which is the best explanation?

A. The air gap slowed thermal energy moving out through the lid, both in the afternoon and at night.B. The second sheet let more sunlight in, so Frame B took in more energy by day and kept it at night.C. The two plastic sheets rubbed together in the wind and made thermal energy inside Frame B.D. The air gap held cold air from the night before, which kept Frame B's air from cooling off.

4.

Frames B and D have the same double lid, but Frame D also holds four black water jugs. Frame D was 11 °C cooler in the afternoon and 4 °C warmer at night. Which explanation fits both results?

A. The jugs shaded Frame D from the sunlight, so less energy got into the frame by day or by night.B. The jugs gave off cold in the afternoon and then gave off heat after the sun went down.C. The jugs took in energy from sunlight during the day and gave it back to the air at night.D. The jugs made new thermal energy at night, because water warms up when the air turns cold.

5.

Use Table 2.

From 6 PM to 6 AM, the jug surface in Frame D cooled by °C, while the air in Frame A cooled by °C.

6.

Use Table 2. Which statement best describes the energy transfer in Frame D at 2 AM?

A. Cold moved in from the night air, through the lid, and into the jugs and the frame's air.B. Thermal energy moved from the outside air into the frame, because the frame was warmer.C. No energy moved, because the jugs and the frame's air were both above freezing at 2 AM.D. Thermal energy moved from the jugs into the frame's air and from that air out to the night.

Part 2: Choose and improve a cold frame

Use the passage, both tables and what you know about thermal energy transfer to answer questions 7–11.

7.

Complete Ayasha's summary of Frame D. Use words from the word bank. Two words are not used.

During the day, the black jugs energy from sunlight, so the air in Frame D warms than the air in Frame B (compare their afternoon highs in Table 1). At night, thermal energy moves from the jugs the cooler air of the frame. The double lid the energy moving out into the night.

8.

Frame E had the warmest night and the coolest afternoon of all five frames. What is its drawback?

A. Its night low of 7 °C is too warm for pepper and tomato seedlings.B. Its materials cost $42, which is over the $40 limit for one frame.C. Its afternoon high of 29 °C is above the 35 °C limit for the seedlings.D. Its double lid lets in too little sunlight to warm its eight jugs.

9.

Ayasha wonders whether painting the jugs black really matters. Which plan is the fairest test of that idea?

A. Build a copy of Frame D with unpainted jugs and a single lid, and test it beside Frame D on one night.B. Build a copy of Frame C with four unpainted jugs and test it beside Frame C on the same day and night.C. Build a copy of Frame C with eight unpainted jugs and test it beside Frame C on the same day and night.D. Paint Frame C's jugs white and test it next week, then compare it with Frame C's results in Table 1.

10.

A neighbor sets up a copy of Frame D. The next day is cloudy and cool, and the night that follows is clear and frosty, just like Ayasha's test night. Which prediction fits Ayasha's results?

A. The frame will likely be warmer that night than in the test, since cool days leave more cold in the jugs.B. The frame will likely match the test night, since the jugs hold the same 4 L of water as before.C. The frame will likely be warmer that night than in the test, since clouds keep the double lid warm.D. The frame will likely be colder that night than in the test, since its jugs took in less energy by day.

11.

A neighbor says, "The water jugs keep the frame warm at night because water is a good insulator, like a blanket over the seedlings." Do you agree? Write a claim, give evidence from both tables and paragraph 4, and explain your reasoning about thermal energy transfer.