Tracing Energy Transfer in Heat and Work: Hands Rubbing and Water Evaporation

[krzyrice]

Heat Problem! NEED HELP!

Homework Statement

In each of the following cases, trace the chain of energy transfer (as heat or as work) as well as changes in internal energy.
a. You rub your hands together to warm them one cold day, and they soon become cold again.
b. A hole is drilled into a block of metal. When a small amount of water is placed in the drilled hole, steam rises from the hole.

Homework Equations

I think none

The Attempt at a Solution

a) Energy from the friction when you rub your hands together creates heat. When that friction is gone, the heat is cooled down by the surrounding energy.

b) The drill creates friction with the block of metal. The friction creates sparks which heats up the block of metal and makes the temperature go up. So when the water touches the bottom of the hole, that heat causes the water to evaporate.

Please tell me if that explanation is good enough and if I should add or remove anything.

 

[Shooting Star]

The Attempt at a Solution

a) Energy from the friction when you rub your hands together creates heat. When that friction is gone, the heat is cooled down by the surrounding energy.

b) The drill creates friction with the block of metal. The friction creates sparks which heats up the block of metal and makes the temperature go up. So when the water touches the bottom of the hole, that heat causes the water to evaporate.

Please tell me if that explanation is good enough and if I should add or remove anything.

a) "The heat is lost to the surrounding because the latter is colder than the hands" would be more appropriate.

b) The mention of the sparks is not necessary, because sparks may not fly always. The fact that the metal heats up enough to boil water or at least high enough to increase it's rate of evaporation significantly due to the friction is enough. (Generally, it heats up to more than 100 deg C.)

 

[krzyrice]

thanks for your help. The explanation helped me settled some confusions about this.