Heat Transfer: Spiraling Upward
The Sun warms Earth's surface, but it does so unevenly. Heat is transferred from hot areas to cooler regions. This transfer of heat around the globe causes our changes in weather. Heat transfer can occur in three ways: radiation, conduction, and convection. Radiation is the transmission of energy as waves or particles. The Sun's energy travels to us through radiant energy waves. You feel these energy waves every time you walk into the sunlight. In conduction, heat travels from one molecule to another. Rocks absorb heat and release it by conduction. Convection is heat transfer that results from differences in densities: warm air rises and cool air sinks. In this activity you will observe heat transfer by convection.
Paper; Pencil; Scissors; String; Tape; Candle or lamp (take care when working with candles; do not let paper or other flammable objects touch candle flames); Heat-proof base for the candle
- Draw a spiral on your paper similar to the one in the Figure 14.2. Your spiral should cover the entire sheet of paper. Cut out the spiral along the solid lines.
- Tape the string to the innermost point of the spiral.
- Holding it by the string, suspend the spiral a few inches above the candle or lamp. (Be careful to keep the paper away from the flame.) Steady your hand so that you can hold the spiral still.
- Observe the spiral and notice any motion.
- How did the spiral move when you held it over the candle?
- Why did the spiral move?
- The spiral slowly rotated.
- The spiral moved because warm air from the candle moved upward by convection.
Get a beaker of warm water and add a few drops of red food coloring, stirring to mix. In a separate beaker, mix some ice-cold water with a few drops of blue food coloring. Slowly pour the cold blue water into the warm red water. Describe what happens. How is this an example of convection?
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