Proof of the Heating Power of the Sun

Objectives:

Students describe the results of a single variable experiment. Students make predictions and write conclusions.

Materials

  • A few chocolate bars, (more for day 2, optional)

  • Clear, sealable plastic bags (like Ziploc bags)

  • Permanent Marker

Focus

Ask students to name some of the ways the heat of the sun changes things. Show them the chocolate and plastic bags. Ask them to predict (or recall) what happens to chocolate when it gets hot. Do we have word for that? Melt

Procedure

Put a few pieces of chocolate into a clear plastic bag and seal it. Put an equal amount of chocolate in a second bag and seal it. Mark one bag "A" and the other "B". Tell students that we will put one bag in the sun outside and the other in shade. Students write down predictions in simple sentences of what they think will occur. What is the only difference between the two bags? (whether it’s in shade or sun.)

Go outside and have the students record which bag has been placed in the sun and which is in the shade. Come back in an hour to see that the chocolate in the sun has melted and then hold both bags next to each other. After everyone gets a good look, students line up to pinch each bag at the same time. Have students use adjectives in sentences to write to describe how the chocolate in the sun is now different than the chocolate in the shade. Why did this happen?

Close:

Go inside with both chocolate bags and show the students a unopened chocolate bar, identical to A and B, so we’ll call it case C. Students again make a line and take turns being able to pinch bag A or B with one hand and pinch C in the other hand.

How does the temperature of the bar change how it feels? Do we have a word for that? Melt

Day 2

Make 3 or 4 bags labeled ‘A’ and the same numbered marked ‘B’ . Break apart 3 or 4 bars into equal parts and put each in a plastic bag. Keep an equal portion for case ‘C’ . When the class goes outside, all ‘A’ bags must go in the sun but on different surfaces. All ‘B’ bags must be in the shade but in different shaded areas. If we revisit the bags in 20 or 30 minutes we’ll see the changes already occurring. Did all the shaded areas soften the same? Did the bag ‘A’ in the grass melt as fast as the ‘A’ in the sun?

On a rainy day: From a vocabulary list, say a word and ask if a student can make a complete sentence with it. Repeat a few times and ask students if they can invent sentences too, and of they will write them now in the journals? Where did the heat comes from? What difference did the heat make?

  • heat

  • melt

  • cold

  • freeze

  • solid

  • liquid

  • gas

  • condense

  • evaporate

Guided writing discussions - Have students list other things that melt. Have students list other things that sunlight does for us or provides for us. Encourage speculation of what earth would be like without the sun. Relate this lesson to other water vapor and heat experiments.