Melting Ice Experiment

Overview

This surprising experiment—featured on Good Eats with Alton Brown—reveals how heat transfer, insulation, and moving water affect how quickly ice melts. Students often predict that boiling water melts ice fastest, but the results challenge their expectations.

Objectives

Students will:

Make predictions and test a hypothesis
Compare the effects of still hot water vs. flowing cold water on melting
Understand heat transfer and insulation
Explain results using evidence

Materials

2 ice cubes (similar size)
Pot of boiling water
Sink with running cold water
Timer (optional)
Tongs or spoon for handling hot pot safely

Teacher supervision is required around boiling water.

Experiment Steps

1. Begin With a Question

Ask students:

“Which will melt an ice cube faster—boiling water or cold running water?”

Have students:

Make individual predictions
Share reasoning
Record hypotheses if desired

Remind them: In science, the goal is not to be right—it’s to learn.

2. Set Up the Hot Water

Heat a pot of water until it reaches a full boil.
Keep it on the stove (or transfer carefully to a heat-safe surface).

3. Set Up the Cold Water

Turn on the cold water tap in the sink.
Adjust the stream so it flows steadily.

4. Test the Ice Cubes

Use two identical ice cubes.

Place one ice cube into the pot of boiling water.
Hold the second ice cube under the stream of cold running water.

Observe carefully.
Optional: Use timers to see how long each cube takes to melt.

5. Results

Despite expectations:

The ice cube in the running cold water melts first.

Why This Happens

Heat moves from warm areas to cold areas.

Both the boiling water and the cold tap water are warmer than the ice cube.

In boiling water:

The hot water melts the outer layer of ice quickly.
That melted water becomes very cold.
It stays around the ice cube because the water is still, creating a cold insulating layer.
That layer slows the melting process dramatically.

In running cold water:

Though colder than the boiling water, the tap water is still significantly warmer than ice.
Running water washes away any cold melted water instantly.
This constantly brings in fresh, warmer (relative to ice) water.
Without the insulating cold layer, melting happens much faster.

Conclusion:
Movement of water matters more than temperature alone.

Vocabulary Connections

Heat transfer – movement of heat from warmer to colder areas
Insulation – something that slows heat transfer
Temperature – measure of heat
Hypothesis – a prediction you can test

These terms can be introduced as age-appropriate.

Extensions

1. Try warm tap water vs. cold running water

Which melts faster?
Students can predict and test again.

2. Add salt to one ice cube

Salt lowers freezing point—what happens to melting speed?

3. Use a fan

Blowing air makes ice melt faster—another example of “moving vs. still.”

4. Try still cold water in a bowl

How does flowing vs. still cold water compare?

5. Graphing

Students create bar graphs showing melting times.

Teacher Notes

This experiment builds critical thinking because the “obvious” answer (boiling water) is wrong.
Works beautifully in science fairs or inquiry-based units.
Always supervise children with hot water and boiling pots.

Hot vs. Cold: Which Melts Ice Faster?