Physics Change of State

2009-11-28 7:10 pm

1)Pauline goes hiking on a very hot day and loses 08. kg of water in one hour by sweating. She feels cooler when there is wind blowing over her bdy. Explain briefly.

2) A lady is wearing a facial mask which is mainly composed of water. When the mask is applied to her face, she feels cool.
(a) Briefly explain why water evapourates in terms of molecular motion.
(b) Explain why evapouration hsa a cooling effect.

回答 (1)

天同

2009-11-29 1:04 am

✔ 最佳答案

1. When the sweat evapourates, it requires latent heat. This latent heat is absorbed from the skin, hence a cool feeling is experienced by Pauline. The wind helps the evapouration of the sweat. The stronger wind blows, the more sweat is evapourated.

2.(a) Water molecules with sufficient high energy escape from the mask into surrounding air. Heat then flows from the facial skin to the water in the mask. Water molecules then acquire more kinetic energy. The more eneretic molecules could thus be able to escape into the air. The process then continues.

(b) When water evpourates, it requires latent heat. This latent heat is normally absorbed from the surroundings. Thus causing the surroundings to cool down because of heat flow to the water.

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