Cold ice Cubes

I have two glasses, one with ice cubes and the other, ice cubes and water. By looking at the thermometers in these two glasses, I notice that the temperature drops to, say, - 4 deg C in the glass containing only ice cubes while the temperature of the other glass is very close to zero deg. C. What is the explanation behind ?
- Ooi See Hai (age 66)
Kuala Lumpur, Malaysia

Probably the ice cubes were a bit colder than -4°C to begin with. It would take them a while to warm up in the air, and it takes them a while to cool the thermometer down. So you see the thermometer gradually drop to -4°C. The cold ice cubes in water would quickly cause some of the water to freeze on their surfaces. That releases latent heat, raising the temperature. Once the temperature reaches 0°C, that freezing stops.

Mike W.

(published on 06/16/2015)