The Popping Water Bottle Experiment
Topic: Heat • Air Pressure • Expansion & Contraction
A simple bottle, hot water, and air pressure create a surprising little pop!—and kids love the mystery of why it happens.
Objectives
Students will:
-
Observe how heated air expands
-
Understand why warm air creates pressure
-
Compare results using hot vs. cold water
-
Connect sound to rapid air movement
Materials
-
A sink or washable surface
-
Hot tap water (not boiling)
-
A large plastic or metal bottle with a narrow opening
(sports bottle, juice bottle, etc.)
Steps
1. Warm water setup
-
Place the empty bottle in the sink.
-
Add 1–2 inches of very hot tap water to the bottom.
Safety note: Adults should handle the hot water.
2. Create the “pop”
-
Place the palm of your hand firmly over the opening.
-
Shake the bottle hard for about 3 seconds.
-
Lift your hand off the opening quickly.
-
Listen for a pop! and watch for a small spray of water.
3. Try it with cold water
Repeat the process using cold water.
Notice that it doesn’t pop.
Why It Works
1. Hot water warms the air
When you shake the bottle, the hot water sloshes around and warms the air trapped inside the bottle.
2. Warm air expands
Warm air takes up more space, but your hand is blocking the opening—so the expanding air builds pressure.
3. Releasing the air makes the pop
When you move your hand:
-
the compressed air bursts out quickly
-
any water droplets at the top are pushed out with it
-
the sudden expansion makes the popping sound
4. Cold water doesn’t work
Cold water doesn’t heat the air, so:
-
no expansion
-
no pressure
-
no pop
Key Concepts Students Learn
-
Heated air expands
-
Expanding air increases pressure
-
Sound can be caused by fast-moving air
-
Temperature changes affect air behavior
Extension Ideas
-
Try different bottle shapes and openings
-
Measure water temperature before and after
-
Add a balloon on top instead of a hand
-
Graph the results: “Which bottles popped the loudest?”
Browse:
Find More:
