Re: Will ice melt faster in a dish, tinfoil, or a plastic bag? Why?

Hi there!

Well, I guess it's not simple. There are three ways ice will melt. It can absorb heat radiation from the warm room. Warm air can flow around the ice as the cooled air falls to the ground. Warm air, tinfoil, dish or bag can 'conduct' heat into the ice directly, warming it up. So can warm hands, which is why you should handle it as little as you can.

So - let's think about the three experiments.

Imagine we have a block of ice floating in midair. There is no dish, tinfoil or bag touching it, just air. The water drips off so the ice gets lighter as it melts, which makes it melt faster and so on and so on. You could actually get pretty close by freezing some loops of fine cotton in the ice, then hanging the ice on hooks by the cotton. This kind of experiment - no dish, no tinfoil and no bag - is called a control experiment, because you can see the effect of all three things separately. The ice is in the full glow of the heat radiation of the room, and as the air cools around the ice it falls to the ground, allowing more warm air near the ice and warming it up more quickly.

Next, we wrap the ice in tin foil. The water can still drip out, but maybe not as quickly. This is really important, and may explain the differences in the experiments with tinfoil. Is it always able to leak by the same amount, or are some better sealed than others?. The tin foil also reflects the heat radiation shining at the ice from the warm room, which will keep the ice cooler. So, the tinfoil wrapper should slow down the melting.

Next, we hang the ice in a plastic bag. This keeps all the cold water around the ice, slowing down the cooling a lot. The plastic won't reflect much of the heat radiation away, so it won't be kept cool that way. My guess is that the effect of keeping the water with the ice is much bigger (if I had time I'd go and calculate it just to make sure) so that the ice in the bag will take longer to melt than the ice in the leaky tin foil.

Finally, we put the ice on a plate. Although there is less warm air flow around it because the dish stops the cool air from getting away, the dish itself is in contact with the ice and water and will be heating them really strongly, so the ice will melt very quickly. The effect would be even greater if you used a metal dish like a cooking pot.

All I can suggest is that you tighten up your experimental procedure. Try using good ski gloves to handle the ice, or maybe tweezers. Try making sure all your ice blocks are exactly the same size and shape, and try the control experiment by hanging the ice by cotton from a hook so it's not touching anything. What about the plastic bag and tinfoil experiments? Are they touching anything or are they hanging by thread also? Keep a careful record of what happens and whether the water runs off or stays with the ice. When you've made lots of experiments you should be able to predict how long the ice would take to melt in a different test, like tinfoil INSIDE a plastic bag hanging by a thread!

Good luck!
Best Wishes,
Max
(max.sang@cern.ch)