Activity Introduction

Quick summary: In this experiment students will participate in or observe a simple experiment to find out whether hot or cold water freezes fastest.



General capabilities: Critical and creative thinking.


Year 1 Science


Year 3 Science


Year 5 Science


Year 6 Science


Syllabus outcomesST1-12MW, ST2-12MW, ST2-7PW, ST3-12MW.

Time required: 5 minutes for explaining activity and putting cups into the freezer, need to check cups every 15 minutes.

Resources required: Foam cup with cold water, foam cup with same amount of very hot tap water, freezer, clock or timer, pen.

Safety advice: This activity requires very hot water – depending on student age and ability this activity may be either a student-led experiment or a teacher-led demonstration.

Keywords: Hot water, cold water, freeze.



Teacher Worksheet

Brief summary:



You will need:

  • Foam cup with cold water
  • Foam cup with same amount of very hot tap water
  • Freezer
  • Clock or timer
  • Pen

What to do:

Step 1. Take your two foam cups and label one "hot" and the other "cold".

Step 2. Fill one foam cup with cold water and one foam cup with the same amount of very hot tap water.

Step 3. Place the cups in the freezer at the same time and start the timer.

Step 4. Check the cups every fifteen minutes. To the surprise of most the hot water in fact freezes first!

How does it work?

Known as the Mpemba effect - after a Tanzanian student who noticed that hot ice cream mix freezes faster than a cold - it was in fact first observed by Aristotle, then later Francis Bacon and René Descartes. But while

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Student Worksheet

In this experiment you will be experimenting to see whether hot water or cold water freezes the fastest.


Explain what you think will happen:


Explain what happened:


Explain why you think this happened:

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