# 47. WARM ALL OVER

from Come Fly With Me – Exploring Science through aviation and aerospace concepts.

SUBJECT: Science
GROUP SIZE: Small or Large
TIME: 60 minutes
TYPE OF ACTIVITY: Teacher Demo or Student Investigation
TEACHING STRATEGY: Guided Discovery Discussion
SKILLS: Experimentation Interpreting Data Recording Data
Objectives: To investigate the rate at which different colored materials absorb heat; to investigate the rate at which different colored materials radiate heat; to be able to select a color which would be the best collector of heat and a color which would be the best radiator.

heat radiation and absorption setup diagram

Materials: A radiant heat source (heat lamp or high wattage bulb); two thermometers (-10°C to 110°C); five cans of the same size and material; spray paint in several colors (red, flat black, yellow, green, white); several corrugated cardboard squares (large enough to cover the tops of the cans); a clock with a second hand or a stop watch; water at room temperature; water at 50°C or greater.
Teacher Background Information:

Heat travels through a vacuum by radiation in the form of electromagnetic waves. What is more, light, also traveling in the form of electromagnetic energy, can be absorbed by certain colored materials and changed into heat energy by causing the molecules of the materials to vibrate more rapidly.

Generally, light colored materials (white or shiny) reflect most wave lengths of light and black absorbs most all wave lengths. Therefore, the molecules in a black material receive more energy than shiny material and speed up causing a heat build up.

Many experiments in school texts have students add hot water to containers of different materials to see which are the most efficient insulators. Students are sometimes surprised to find that metal containers get hot very quickly but loose their heat rapidly, also. See, through the following experiment, if the students can discover a possible reason for this. (Metal, while absorbing heat rapidly by conduction, is an efficient radiator also).

A major concern of space travelers is the build up of heat in the space craft. Currently, the Shuttle uses the cargo bay doors as giant radiators to prevent a dangerous build-up of heat. The doors are opened while in orbit to expose shiny silvered coverings which reflect the radiant heat reaching the Shuttle from the Sun in the form of electromagnetic waves. Try to relate the results of this experiment to the application of the concepts to the real situations encountered by space scientists.
Procedure:

1. Prepare cans in several colors with the spray paint and allow to dry thoroughly.
2. Fill two cans with equal amounts of water at room temperature.
3. Place a piece of cardboard, through which you have made a small hole for a thermometer, on top of each can.
4. Insert a thermometer into each cardboard making sure the bulb of each thermometer does not touch the sides or the bottom of the cans but extends into the water.
5. Place the cans on opposite sides of the heat source about 20cm away.
6. Record the temperature of the water in each can every two minutes for twenty to thirty minutes.
7. Now fill each can with the same amount of hot water and record the temperature every two minutes for twenty to thirty minutes.
8. Graph the results.

Which of the cans absorbed more heat by radiation? Which of the cans radiated the most heat energy? Why do you think this is so? What colors do you think would be the best for a spacecraft? Why do you think so? If you were to produce a solar collector to produce hot water, what color would be the most efficient for your device?
Extensions:

Try the experiments using containers made of other materials than metal. Repeat the experiment using empty cans. Explain what may have caused any differences in the results. Do the experiments again placing the cans further away from the heat source. Try using the sun as the heat source.

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