# A physics question about melting ice in a cup **URL:** \ **Category:** Factual Questions\ **Created:** [February 24, 2021, 10:19pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677 "2021-02-24T22:19:16Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Roderick\_Femm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/roderick_femm/32/14875_2.png) [@Roderick\_Femm](https://boards.straightdope.com/u/Roderick_Femm)\ **Post date:** [February 24, 2021, 10:19pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/1 "2021-02-24T22:19:16Z")
Imagine a typical fast-food drink cup, made of some kind of heavy waxy-coated paper, half full of ice with no liquid. It is in a room at (say) 70 degrees F. It naturally starts to melt, gradually changing the ice into water. The question is: will it melt faster\* if left alone, or if the water is removed (say) three times during the melting at roughly equal intervals? \*By “melt faster” I mean complete the process of melting faster, in case that makes a difference to the scenario. In other words, the time starting at point A, all ice, and ending at point B, all water. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [February 24, 2021, 10:23pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/2 "2021-02-24T22:23:22Z")
It will melt faster if the water is left in the cup. Water is a much, much better conductor of heat than air, so if you want the ice to melt, you want as much ice in thermal contact with the walls of the container, and the water will do that better than air. ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [February 24, 2021, 10:29pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/3 "2021-02-24T22:29:21Z")
It would be easy to test with constant water removal. Just use two identical cups of ice, but put a hole in the bottom of one. ---
**Author:** ![Roderick\_Femm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/roderick_femm/32/14875_2.png) [@Roderick\_Femm](https://boards.straightdope.com/u/Roderick_Femm)\ **Post date:** [February 24, 2021, 10:49pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/4 "2021-02-24T22:49:35Z")
Thank you both, asked and answered. ---
**Author:** ![YamatoTwinkie](https://avatars.discourse-cdn.com/v4/letter/y/cc9497/32.png) [@YamatoTwinkie](https://boards.straightdope.com/u/YamatoTwinkie)\ **Post date:** [February 24, 2021, 10:58pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/5 "2021-02-24T22:58:45Z")
I thought I’d like to previous discussion on this subject: > [@How To Keep My Cooler Longer?](https://boards.straightdope.com/t/how-to-keep-my-cooler-longer/459792/11): > > If you’re talking about getting warm (or room temperature) stuff cold, you want ice + water (if you add salt it’ll get colder faster), but if your beers are already cold you don’t need (or want) to transfer heat faster, you want to prevent the transfer of heat. My impression of the original post was that we’re adding new ice to a cooler in which the old ice has melted, and the beers are already cold. The key to keeping stuff cold, and making the ice last longest, is to get rid of the melt wate… > [@Keeping beer cold.](https://boards.straightdope.com/t/keeping-beer-cold/30708/4): > > If you can remove the water and replace it with COLD air, than yes, draining the water is a good idea. If you are replacing the water with WARM outside air, it’s better to leave the water in place. > [@Ice Cooler Performance](https://boards.straightdope.com/t/ice-cooler-performance/543868): > > Will an ice cooler (standard Igloo/Rubbermaid type plastic ice cooler with lid) perform better over time on a hot summer day if you periodically drain the water from melted ice? I say keep the water in there, since when you drain the ~32 degree water you are effectively replacing that volume with ambient air and thus accelerating the melting of more ice. My brother-in-law insists the cooler will last longer (keep the beer colder longer) if you drain the water. He cites the second law of therm… > [@Adding ice to an ice chest](https://boards.straightdope.com/t/adding-ice-to-an-ice-chest/635837): > > Given an ice chest containing ice and water (the water being ice that has melted), is it better to empty the water (in the ice chest) before adding more ice? Or just add the ice without emptying? This issue has been hotly debated around our campsite. My friends say, “the water is 32 degrees, don’t throw it out”. But I am thinking if it is 32 degrees then why isn’t it frozen? Please help settle this. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [February 25, 2021, 1:28pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/6 "2021-02-25T13:28:36Z")
> [@beowulff](#): > > It will melt faster if the water is left in the cup. This sounds right to me. FWIW I’m a physicist who has specialized in heat, temperature, and heat transfer for the last 20 years. ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [February 25, 2021, 7:51pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/7 "2021-02-25T19:51:09Z")
> [@california\_jobcase](#): > > Just use two identical cups of ice, but put a hole in the bottom of one. In my sink now are two plastic cups, one with holes in the bottom, both with 3 ice cubes, weighing an identical 66g. It is 2:50pm, I will advise as the experiment progresses. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [February 25, 2021, 7:56pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/8 "2021-02-25T19:56:13Z")
Science! [![](https://img.youtube.com/vi/V83JR2IoI8k/maxresdefault.jpg "Thomas Dolby - She Blinded Me With Science (Official Video - HD Remaster)") ](https://www.youtube.com/watch?v=V83JR2IoI8k) ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 25, 2021, 7:59pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/9 "2021-02-25T19:59:13Z")
Dry air is a terrible conductor. In a cup of melting ice the air won’t stay dry long, but it is mostly the water content in the air that is contributing to any melting when the ice is not submerged in water. ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [February 25, 2021, 9:03pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/10 "2021-02-25T21:03:25Z")
Man, that is some slow-melting ice! ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [February 25, 2021, 9:13pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/11 "2021-02-25T21:13:55Z")
At 4:10 I have about a quarter inch of liquid water in the cup without holes. There appears to be more melting in that cup despite the tiny amount of liquid. This is taking a lot longer than I expected. Must be hard water. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [February 25, 2021, 10:15pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/12 "2021-02-25T22:15:57Z")
At least we know you’re not in Texas where ice would be forming in the cup in your kitchen, not melting. ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [February 25, 2021, 10:45pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/13 "2021-02-25T22:45:24Z")
Were you keeping the ice at liquid helium temps? I’m amazed that three ice cubes can take so long to melt. ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [February 25, 2021, 11:36pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/14 "2021-02-25T23:36:25Z")
6:30 the ice is almost completely melted. The cup with the water is clearly more melted than the draining cup. Longest lasting ice ever. I also got in trouble for leaving the ice cube tray on the counter. Science is sacrifice. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [February 26, 2021, 12:03am UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/15 "2021-02-26T00:03:07Z")
That indeed was last week for me. We had no ice for a long time due to our water being contaminated. ---
**Author:** ![filmore](https://avatars.discourse-cdn.com/v4/letter/f/7993a0/32.png) [@filmore](https://boards.straightdope.com/u/filmore)\ **Post date:** [February 26, 2021, 12:10am UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/16 "2021-02-26T00:10:29Z")
Back before refrigeration, one of the first ways ice cut from lakes was stored was by suspending large blocks of ice below ground level with air surrounding the blocks. You can see an example of the ice barn at about minute 4 of this clip: > **[How We Got to Now | The Development of the Ice Trade | Episode 5 | PBS](https://www.pbs.org/video/how-we-got-now-episode-cold/)** > > Steven tells how Frederic Tudor developed a method of transporting ice to warm climates. The air around the ice was such a good insulator that they could store ice like this for months in the South to be sold over the summer. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 26, 2021, 2:49am UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/17 "2021-02-26T02:49:46Z")
Wasn’t it more common to store it long-term in the North, and ship it south as needed? It still lasted through the summer, of course, but northern summers aren’t as hot as southern ones. ---
**Author:** ![filmore](https://avatars.discourse-cdn.com/v4/letter/f/7993a0/32.png) [@filmore](https://boards.straightdope.com/u/filmore)\ **Post date:** [February 26, 2021, 4:22am UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/18 "2021-02-26T04:22:23Z")
The show was about one of the first people to figure out the ice trade. He had tried many ways of storing and shipping ice before figuring out that having air gaps worked to provide good insulation. But I’m sure that as ice was commercialized, they worked out any inefficiencies in the system and would have done things like store it in the North. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [February 26, 2021, 8:15am UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/19 "2021-02-26T08:15:08Z")
> [@LSLGuy](#): > > Science! I swear allegiance to the physical sciences… and enmity to the occult in all its forms… [![]( " - YouTube") ](https://www.youtube.com/watch?v=_b7cVTtbCO8&t=2536) ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [February 26, 2021, 4:07pm UTC](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677/20 "2021-02-26T16:07:36Z")
> [@TriPolar](#): > > Dry air is a terrible conductor. In a cup of melting ice the air won’t stay dry long, but it is mostly the water content in the air that is contributing to any melting when the ice is not submerged in water. How’s that? Dry air and water vapor aren’t hugely different in their conductivities. Water’s a bit better because it is a lighter gas, but it’s not twice as good. However, a quick look at a psychrometric chart shows saturated air around icewater will only be around half a percent water, so almost all the conductivity will be from the nitrogen and oxygen. The water vapor will make a difference that would be hard to detect even with nice expensive instruments. [Next page](https://boards.straightdope.com/t/a-physics-question-about-melting-ice-in-a-cup/933677.md?page=2)