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Name: Laura L.
Status:  educator
Age: 30s
Location: N/A
Country: N/A
Date: 2/21/2004


Question:
Why do ice cubes make a cracking sound when put in water or soda or some kind of drink?


Replies:
- When ice cubes freeze air is trapped inside. That is what makes ice cubes in your refrigerator look hazy. When you drop an ice cube into warm soda or water, the ice cube warms up faster than it can melt, so that the trapped air expands inside the melting cube. This increase in the internal pressure causes the ice cube to crack and that is the sound you hear.

Vince Calder


What is actually happening is known as thermal stress. When you pour warm water or soda over a cold ice cube, the difference in temperature causes problems for the ice cube. The outside of ice cube starts to warm up (pay little attention to the melting at this point), but the inside is still rather cold. All materials have a property know as the coefficient of thermal expansion which is a function of how much something will lengthen if it grows in temperature. In other words, as the temperature gets higher, the crystals on the outside of the ice want to expand or lengthen, but the crystals still in the middle do not see this new temperature yet, and they do not want to expand. These two different layers of the outside wanting to grow and the inside not wanting to grow create stress in the ice cube. The ice cube can only take so much of this stress until it breaks. The cracking you hear is the ice cube breaking to relieve this stress. Thanks for using NEWTON.

Christopher Murphy
Associate Mechanical Engineer
AFRL/PROE


Laura,

The soda is warmer than the ice. In general, things expand when heated. The warmer soda causes the outside of the ice to expand a little too fast to stay together, Thus, the cubes sometimes crack -- that is the sound you are hearing.

Regards,
ProfHoff 809



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