## Concept of "Cold"

Mahir Pepic 3F
Posts: 15
Joined: Fri Sep 25, 2015 3:00 am

### Concept of "Cold"

I recently read that there is no such thing as "cold" according to thermodynamics. The sensation of "cold" is actually really just an absence of heat. How then, does does adding ice to hot coffee cause it to become more cold if we are just adding quantities of substance that are close to/absent of heat?

Satyam Kotecha 1C
Posts: 10
Joined: Fri Sep 25, 2015 3:00 am

### Re: Concept of "Cold"

Adding ice to hot coffee lowers the temperature of the overall substance because the heat from the coffee transfers to the ice therefore "filling" in the absence of heat of the ice resulting in a decrease in temperature of the coffee.

Aashi_Patel_3B
Posts: 20
Joined: Wed Sep 21, 2016 2:57 pm

### Re: Concept of "Cold"

This is simply the second law of thermodynamics: how heat flows naturally from an object at higher temperature to an object at lower temperature. You need work to force the heat in the other direction (this is what Air Conditioner and Refrigerators do). I agree with the example stated above: it really simplifies the concept.

Grace_Bower_2B
Posts: 13
Joined: Wed Sep 21, 2016 2:58 pm

### Re: Concept of "Cold"

First of all, consider the ice the 'system' and the coffee the 'surroundings'. The melting of the ice is an endothermic reaction, it requires heat to occur, so the q of the system increases. According to the first law of thermodynamics, the q of the system = —q of the surroundings, so if the q of the system is increasing, the q of the surroundings is decreasing. Therefore the surroundings (the coffee) is cooled.
Conceptually heat and a cold are a lot like light and dark. There is technically no such thing as 'darkness' only the absence of light. Cold is merely our word for the absence of heat.

Cynthia Bui 2H
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: Concept of "Cold"

You feel cold when heat is flowing out of you and feel warm/hot when heat is flowing into you (say your hand when you hold a hot cup of tea). The temperature decreases when you add ice because heat is being transferred into the ice away from the liquid, lowering the temperature of the liquid.

Ruth Glauber 1C
Posts: 100
Joined: Wed Sep 18, 2019 12:20 am

### Re: Concept of "Cold"

Is there an example in the textbook that anyone could explain?