Thermodynamics: Ice Pack!

This is a video of my freezer and an ice pack inside. Last week, my back was feeling sore for some reason, so I alleviated the pain by icing it. Ice is cold, so when you apply it to a sore spot, it makes it feel better. However, unlike what I used to think in my less enlightened days, your skin does not become cold because the coolness of the ice pack seeps into your skin. No, on the contrary, it is quite the opposite. Energy flows from the object with the higher temperature to the object with the lower temperature, and this energy is called heat. Our book defines heat as thermal energy transferred between objects because of a difference in their temperatures. This means that the heat from my body flowed from my body to the ice pack. This loss of heat is the reason why my back became cold. At the same time, the ice pack gained heat, which is why it became warm after a while. My back would have a negative Q value and the ice pack would have a positive Q value. When the ice pack became warm, I stuck it back in the freezer where it could lose its heat to the surrounding cold and become cold again too.

I'm sure someone has said to all of us at least once in our lives, "Don't leave the freezer (or refrigerator) door open for too long because you'll let all the cold air out!" Thanks to our study of thermodynamics, now we all know that this remark is not true. The cold air does not leave the freezer or refrigerator. Instead, all the warm air flows into the freezer or refrigerator since energy flows from the object with the higher temperature to the object with the lower temperature. When you think about this, it makes sense because air with a higher temperature has faster moving molecules, which means that these air molecules would be the ones to travel into a new place, therefore increasing the energy in the new place. The slower moving molecules in the freezer or refrigerator would not have enough energy to travel out into the kitchen.