Learning Lesson: Canned Heat

Overview

Different colored objects absorb energy at different rates. That is partially due to albedo. Albedo is the amount of reflection from a surface. The demonstration will show that water in a dark colored can will have a higher temperature after exposure to the sun than water in a shiny can.

TOTAL TIME 2 hours
SUPPLIES Two empty metal coffee cans, (3 lbs size), Thermometer, "Flat White" and "Flat Black" spray paint
PRINTED/AV MATERIAL None
TEACHER
PREPARATION
One coffee can should to be painted flat white inside and out. The other can should be painted flat black inside and out. (You may neet to first spray "Primer" on the cans so the paint will adhere.)
SAFETY FOCUS Summer weather Safety

Procedure

  1. Fill the two cans with about two inches of cold water.
  2. Measure the temperature of the water in each can. (The readings should be the same.)
  3. Remove the thermometer and place the cans in a sunny location where they will not be disturbed and receive two hours of sunlight.
  4. After two hours, measure and compare the water temperature in each can.

Discussion

The darker and duller an object, the more energy that object absorbs. The lighter colored or shiner an object, the less energy that its absorbs. But how does the water temperature change?

For some objects, like water and glass, light passes through with little direct heating effect. The water is heated by the energy absorbed then emitted by the cans. For white or shiny metallic surfaces, the energy isn't absorbed very quickly either, as some is reflected away. For a black material, light and heat are almost completely absorbed with little reflection.

Heated bodies also emit energy. The more energy an object absorbs, the more it radiates. The water in the white can was not as warm as in the black can because the white can absorbed less energy and therefore has less energy to radiate into the water. This type of radiation, where color affects the ammount of radiation absorbed, is called "black body radiation".

Live weatherwise

Avoid the Heat

Stay out of the heat and indoors as much as possible. Spend time in an air conditioned space. Only two hours a day in an air-conditioned space can significantly reduce the risk of heat-related illness. Shopping Malls offer relief if your home is not air-conditioned.

If air conditioning is not available, stay on the lowest floor out of the sunshine. Remember, electric fans do not cool, they just blow hot air around.

Dress for the heat

Wear loose-fitting clothes that cover as much skin as possible. Lightweight, light-colored clothing reflects heat and sunlight and helps maintain normal body temperature.

Protect face and head by wearing a wide-brimmed hat. Avoid too much sunshine. Sunburn slows the skin's ability to cool itself. Use a sun screen lotion with a high SPF (sun protection factor) rating.

Do not drink IN the Heat

Drink plenty of water and natural juices, even if you don't feel thirsty. Even under moderately strenuous outdoor activity, the rate your body can absorb fluids is less than the rate it loses water due to perspiration.

However, if you have epilepsy or heart, kidney, or liver disease; are on fluid-restrictive diets; or have a problem with fluid retention, you should consult a doctor before increasing liquid intake.

Eat for the Heat

Eat small meals more often. Avoid foods that are high in protein because they increase metabolic heat. Avoid using salt tablets, unless directed to do so by a physician.

Living in the Heat

Slow down. Reduce, eliminate, or reschedule strenuous activities such as running, biking and lawn care work when it heats up. The best times for such activities are during early morning and late evening hours. Take cool baths or showers and use cool, wet towels.