The Melting Ice Challenge
Two students are racing to melt identical ice cubes on a warm day. Student A wraps her ice cube in a wool sock. Student B places his ice cube on a metal tray in the sun. After 10 minutes, Student A's ice cube has barely melted, while Student B's ice cube has melted almost completely into a puddle. Student A says, "That's impossible-wool is warm, so it should melt the ice faster." Student B says, "Metal is cold, so it should melt the ice slower." Both students are surprised by the results. The teacher asks them to explain what actually happened using ideas about how heat moves.
1. Explain why Student A's ice cube melted more slowly even though wool feels warm.
Read the worked answer
Wool feels warm to the touch because it traps body heat, but it does not create heat. Wool is a good insulator, meaning it slows the movement of heat. When wrapped around the ice, the wool slows heat from the warm air from reaching the ice, so the ice melts slowly.
The key idea: an insulator does not add heat; it slows heat transfer. Student A's reasoning confused 'feels warm' with 'adds heat.' The wool kept the surrounding warmth away from the ice, so it melted more slowly than the unwrapped cube.
2. Explain why the metal tray made Student B's ice cube melt faster, even though metal feels cold.
Read the worked answer
Metal feels cold because it conducts heat away from your hand quickly, not because it is actually cold. Metal is a good conductor, so it moves heat quickly. The metal tray was warmed by the sun and the air, and it transferred that heat to the ice quickly, melting it fast.
The key idea: a conductor speeds up heat transfer. Student B confused 'feels cold' with 'has no heat.' The metal was actually helping heat move into the ice, which is why it melted almost completely in 10 minutes.