When an ice pack is placed on the ankle, what is the direction of heat transfer?

• A. The ankle loses thermal energy to the ice pack.
• B. The ice pack loses thermal energy to the ankle.
• C. No energy transfer occurs.
• D. Heat is generated in the ice pack.

Answer: (A)

Heat moves from warmer to cooler objects. The ankle is warmer than the ice pack, so when they touch, heat flows into the ice pack by conduction. The ankle loses thermal energy to the ice pack, while the ice pack gains energy (often melting as it absorbs heat). Transfer continues until temperatures are near equal. So the direction described—the ankle losing thermal energy to the ice pack—is the correct one.