(a) When you exercise vigorously, you sweat. How does this help your body cool? (b) A flask of water is connected to a vacuum pump. A few moments after the pump is turned on, the water begins to boil. After a few minutes, the water begins to freeze. Explain why these processes occur.

When you exercise vigorously, your body generates heat, which increases the core temperature. Sweating is a natural process that helps regulate body temperature. When sweat is produced, it's released onto the skin's surface. As the sweat evaporates, it absorbs energy (heat) from the skin, which leads to a cooling effect. To summarize the cooling process of sweating: 1. You exercise, generating heat and increasing core body temperature. 2. To avoid overheating, your body produces sweat. 3. Sweat covers the skin surface and absorbs heat from the skin as it evaporates. 4. The skin cools as heat is absorbed by the evaporating sweat, ultimately helping to control body temperature.

This interesting phenomenon of water boiling and freezing in a flask connected to a vacuum pump can be explained by changing pressure conditions inside the flask and their impact on the water's boiling and freezing points. 1. When the vacuum pump is turned on, it removes air molecules (and hence pressure) from inside the flask. This lowers the boiling point of the water. 2. Due to the lowered pressure, the boiling point of water becomes lower than the temperature of the water, causing the water to start boiling. 3. As the water boils, it changes from a liquid to a gas, which is an endothermic process (absorbs heat). As the boiling process absorbs heat, the temperature of the remaining water starts to decrease. 4. If the vacuum pump continues to lower the pressure inside the flask, the temperature of the remaining water will eventually reach its freezing point under the new pressure conditions, causing the water to freeze.

In this exercise, we explained two thermodynamic processes: the cooling effect of sweating and the boiling and freezing of water in a flask connected to a vacuum pump. Sweating cools the body by evaporating sweat and absorbing heat from the skin, while water boils and freezes in a flask connected to a vacuum pump due to changes in pressure, ultimately resulting in the lowered boiling point of water and heat absorption during the change from liquid to gas, eventually reaching the freezing point at the new pressure conditions.