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How Does Ice Cool Drinks?

Drop a few ice cubes into a glass of water at room temperature, and in a few minutes the water will cool. How does this work?

ice cubes close up

Photo: lkthinh2002 (Flickr)

Ice cubes are a great way to cool a drink.

Here’s something we tend to take for granted: drop a few ice cubes into a glass of water at room temperature, and in a few minutes the water will cool. How does this work?

Molecules In Water

Heat is a measure of molecular activity: the faster a thing’s molecules move, the more heat that substance contains. And because everything is made of molecules, and molecules are in constant motion, everything contains at least some heat.

As we know, ice is colder than room temperature water. Because ice molecules move slowly and cluster tightly together, they produce a relatively low amount of heat. When ice is placed in a glass of water whose molecules are moving at a greater rate, the ice begins to absorb energy, because heat always travels from regions of relative warmth to colder areas in order to equalize temperatures. In other words, ice absorbs heat from the water.

As the water molecules lose energy, they begin to slow down, and consequently to cool. So, it’s kind of the opposite of what we might think: when we put ice in water, the ice doesn’t give its cold to the water, it takes heat from the water.


The cooling process actually happens in stages. Because ice floats, it cools the water near the top of the glass first. As the top layer of water cools, its density increases, causing it to sink to the bottom. The lower layer, less dense and therefore more buoyant, floats to the top and is cooled in turn.

  • meera joey

    let say if the choices for the answers are:
    A. molecular collision decrease
    B. kinetic energy decrease

    what would be the best answer for it?

  • sammy

    if molecular collisions decrease., there ll be no efficient energy transfer….and since the ice cubes take up enegy to break bonds within itself, kinetic energy increases…so the choices dont make much sense….if u could maybe explain further.

  • Silas Knight

    I have always wondered why ice does what it does. I had always just assumed that the cold water from the ice mixed with the warmer water in the cup. However, the scientific process is a lot more interesting. Especially the stages of cooling. Thanks for sharing!

  • John Smith

    What would be the best moment and best shape of the ice to cool, lets say, a bath tub filled with 50F degree water?

    It seems some water containers have shown in experiments to be at lowest temperature after 30 minutes after ice was added, and would crushed, cubed or block ice create the lower temperature?

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