The Amazing Water Trick

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Using two baby food jars, food coloring, and an index card, you'll 'marry' the jars to see how hot water and cold water mix. Besides illuminating the cool fact that an index card can act as a lid (with no water gushing out), this activity also teaches about the differing densities of hot and cold water.

Quick Guide

Preparation Time:
Under 5 minutes

Learning Time:
5 to 10 minutes

Estimated Materials Cost:
$1 - $5 per group of students

Age Range:
Ages 6 - 11

Resource Types:
Activity, Experiment/Lab Activity


Materials List (per group of students)

  • Two identical small, wide-mouthed jars (baby food jars are perfect)
  • Hot water
  • Cold water
  • Food coloring
  • Index cards or squares of waxed paper
  • Scissors
  • A large, shallow baking pan (if you don't have one, do this activity in the sink--it can be messy)


  • Physical Sciences
    • Heat and Thermodynamics
      • Heat and Temperature
    • States of Matter
      • Liquids
    • Structure and Properties of Matter
      • Volume and Density


To use this activity, learners need to:

  • see
  • touch

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access


  • Murphy, Pat ; Klages, Ellen ; Shore, Linda


  • All rights reserved, The Exploratorium, 1998