Lab / experiment Grade 2 Science
The Cold Cup at Dunnetts School: Where Did the Drops Start?
Grade 2 groups compare a cup of dyed ice water with a cup of dyed room-temperature water to find out whether the drops on a cold cup leaked through it.
Objectives
- Students will compare a cold cup and a room-temperature cup over twenty minutes.
- Students will use the color of the drops as evidence about where they came from.
- Students will argue that cooling caused the drops and that warming undoes it.
Vocabulary
Key words: cold, drops, outside, dry, evidence, air
Teacher overview
A cup of ice water left on a desk at the fictional Dunnetts School turns wet on the outside within minutes, and many second graders explain that wetness the same way: the water leaked out through the cup. This lab tests that explanation directly by dyeing the water inside both cups blue and sealing the tops, so that any water arriving from inside would arrive blue and none could slosh over the rim. A second cup of room-temperature water, treated exactly the same way, stays dry, which leaves the cold as the only thing that differs. The last step pours warm water into the first cup and finds the outside dry again, giving students the reversal they need for an argument that cooling caused the change.
Procedure
Step 1. Your teacher will put blue coloring in two pitchers of water. One pitcher is cold with ice. One pitcher is room temperature. Do not drink any of this water.
Step 2. Your teacher will fill Cup A with cold water and ice. Your teacher will fill Cup B with room-temperature water. Both cups get filled to the same line.
Step 3. Put a square of plastic wrap over the top of each cup. Hold each one on with a rubber band. Now nothing can splash out.
Step 4. Wipe the outside of both cups with a dry paper towel. Both cups must start dry.
Step 5. Set each cup on its own dry paper towel. Start the timer.
Step 6. At 10 minutes, touch the outside of each cup with one dry finger. Write wet or dry in the first table.
Step 7. At 20 minutes, look at the outside of each cup again. Look at the color of any drops. Look at the paper towel under each cup. Write what you see in the first table.
Step 8. Now your teacher will pour the cold water out of Cup A and pour warm tap water in. Wipe the outside of Cup A dry again. Wait 10 more minutes. Then check the outside of Cup A and write wet or dry in the second table.
Step 9. Wipe up any spills so the floor stays safe. Wash your hands when you finish.
Data & Analysis
Table 1. What the two cups did.
| Cup | What is inside | Outside at 10 minutes | Outside at 20 minutes | Color of the drops |
|---|---|---|---|---|
| A, cold water and ice | ||||
| B, room-temperature water |
Table 2. Cup A after the warm water went in.
| Cup A with warm water | Outside at 10 minutes |
|---|---|
- Which cup got wet on the outside, A or B?
- Both cups held blue water. What color were the drops on the outside of Cup A?
- The drops were not blue. Tell what that says about where they came from.
- Cup B stayed dry. Name the one thing that was different about Cup A.
- Your teacher put warm water in Cup A. What did the outside of Cup A do then?
- Some people say the water leaked out through the cup. Name two things you saw that say otherwise.
- The drops did not come from inside the cup. Where were they before they landed on the cup?
- Name one other cold thing you have seen get wet on the outside.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: Cup A, the cold one. Accept the answer that matches the group's own table, which in nearly every room is Cup A.
- Answer: Clear. The drops on the outside had no blue in them at all, even though the water inside was blue.
- Answer: It says the drops did not come from inside the cup, because water from inside would have carried the blue coloring with it.
- Answer: The cold. Cup A held ice water while Cup B held room-temperature water, and everything else about the two cups was the same.
- Answer: It stayed dry, or it dried up and no new drops formed. Accept the result the group actually recorded in the second table.
- Answer: Accept any two of these: the drops were clear and not blue, the plastic wrap kept anything from splashing over, Cup B held the same kind of water and stayed dry, and Cup A stayed dry once warm water went in.
- Answer: In the air around the cup. Accept any answer saying the water was in the air in the room before the cold cup made it gather into drops.
- Answer: Accept any real example, such as a cold can from the refrigerator, a window on a cold morning, a bathroom mirror, or an ice cream carton set on a table.
Differentiation
Support
Run Cup A and Cup B as one demonstration pair at the front and give these students a table with wet and dry printed as choices to circle. Have them touch the outside of both cups at the 10-minute check so the difference reaches them by hand as well as by eye.
Extension
Ask a group to set up a third cup of ice water with no plastic wrap and compare its outside with Cup A at 20 minutes. Have them write whether the open top changed the result and what that adds to the argument in question 6.
ELL supports
Hold up one dry cup and one already sweating cup side by side and label them with the words dry and wet before the lab begins. Provide the word bank cold, warm, wet, dry, clear, blue, and allow questions 1, 2, and 5 to be answered by circling a word or pointing at a cup.
Extensions
Breathe on a cool window or a small mirror and look at what appears, then wipe it and warm the mirror in your hands before breathing on it again. Ask students whether this matches what Cup A did and what the warm water step showed.