What Factors Affect the Rate of Heat Loss?

[franz32]

Hello again...

1. Some claim that the freezer makes ice faster if one pours boiling water instead of cold water on the ice trays. Is this true? How come?

2. If one intend to drink a coffee soon, he has to stir it with teaspoon. How does that help?

3. How does a thermos bottle keep the water inside hot for a longer period? First of all, what is all about the structure of the thermos bottle?

4. Would there be a faster or slower rate of fall in temperature of a hot substance placed in vacuum at lower temperature? Why or why not?

 

[HallsofIvy]

1. There is no "how come"- it's false! The colder the water is to start with, the less time it will take to get to freezing.
(It is true that is you boil water before freezing it, you take some dissolved air out so that the ice cubes will be clearer- looks nicer at parties!)

2. Stirring with a spoon (I wasn't aware it had to be a teaspoon- why not use a coffee spoon?) exposes more of the coffee to the cooler air and incorporates some air into the coffee itself.

3. A thermos bottle has vacuum between the bottle itself and its outside cover. heat cannot conduct through vacuum.

4. Faster or slower than what? If you mean "than if it were not in a vacuum", being in a vacuum means it is not in contact with anything (like air) cooler than itself and so no heat conducts away. It will still lose heat through radiation but it will lose heat slower.

 

[Hexfire]

wait a minute...

hhmmmmm... for some reason... those questions sound very familar... they're a post lab assignment!

Who are you franz32? from manila... hehe... you're a student aren't you...?