Crush a Bottle Using Thermal Contraction!

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Science experiments are so much fun partly because, well, they’re science, but partly because they seem like magic for young children. Today’s experiment is no exception – we crush a bottle without using our hands!

This experiment highlights the relationship between temperature, pressure, and the behavior of gases. We use temperature to change the pressure inside of the bottle rapidly. This rapid change makes the air pressure in the bottle lower than the air around it, causing it to contract and crush.

The kids will be amazed by this experiment!

How to make the Crush a Bottle Using Thermal Contraction STEM experiment

Supplies you will need

For this experiment, you’ll need:

• Plastic 2L bottle
• Bowl or casserole dish (2L bottle can lie flat in it)
• Hot water
• Cold water
• Ice
• Optional: funnel

Here is a fun book involving all things pressure (water and air pressure) that has educational pictures to accompany the explanations!

Before you start

Placing a towel under your experiment would be helpful since it can drip on the surface you’re using.

Please watch fingers around the hot water.

Instructions

Here is how to do this experiment with your child:

Step 1: Pour very hot water in the 2L bottle and place cap back on

Carefully pour hot water into the 2L plastic bottle. If needed, use a funnel to help pour the water in.

Add about 4″ of hot water to the bottle and let it sit, cap open, for about 2-3 minutes. In this step, we are heating up the air inside of the 2L bottle before adding the cap back on.

This is crucial because the air inside the bottle expands when it’s heated, and this expansion is what creates the pressure difference that causes the bottle to collapse when it’s submerged in cold water.

If you cap the bottle too soon, the air inside won’t have enough time to heat up fully, and the pressure difference won’t be as significant. As a result, the bottle may not collapse or may only partially collapse.

Place the cap back on the bottle and ensure there are no leaks.

Step 2: Add ice and water to the bowl

Add some ice and water to the bottom of the bowl or casserole dish before you place the bottle in. Then, place the 2L bottle on its side in the dish. It should be able to fully fit inside of the dish.

Next, pour ice-cold water over the bottle. If the bottle does not start to crush right away, just keep scooping up more ice water from the dish and pouring it over the bottle. It will eventually start to crush!

Step 3: Take the bottle out and observe

As you continue to pour more ice water on the bottle, the bottle will continue to crush.

As the warm air inside of the bottle cools, it exerts less pressure. The air pressure outside of the bottle is stronger than inside, so it crushes the bottle.

The STEM behind the Crush a Bottle Using Thermal Contraction STEM experiment

This experiment teaches:

• Thermal expansion and contraction
• Air pressure
• Close observation

How it works

This experiment highlights the relationship between temperature, pressure, and the behavior of gases.

Since temperature is directly proportional to kinetic energy, when we increase the temperature inside the bottle, we also increase the kinetic energy. That increase in kinetic energy causes the air molecules in the bottle to move more rapidly and spread out, leading to an overall increase of air pressure in the bottle.

Placing the bottle in cold water decreases the temperature of the air and the kinetic energy in the bottle, decreasing the air pressure in the bottle. Since the outside air pressure (the air outside of the bottle) remains the same, we see a large pressure difference and the bottle crushes.

Thermal expansion and contraction

At the heart of this lies the concept of thermal expansion and contraction. When the bottle is filled with warm water, the air inside also warms up. As a result, the air molecules gain kinetic energy, causing them to move more rapidly and spread out. This expansion leads to an increase in the volume of the air within the bottle.

Once the bottle is sealed and placed in cold water, the temperature of the air inside begins to decrease. Consequently, the air molecules lose kinetic energy, causing them to slow down and move closer together. This contraction results in a decrease in the volume of the air within the bottle.

Air pressure

The key to understanding why the bottle crushes lies in the pressure differential that arises. As the air inside the bottle contracts, the pressure inside decreases. However, the atmospheric pressure outside the bottle remains constant. This creates a significant pressure difference between the inside and outside of the bottle.

The flexible nature of the plastic bottle allows it to succumb to this pressure imbalance. The external atmospheric pressure, being greater, exerts a force on the bottle, causing it to deform and eventually collapse inward.

Close observation

This experiment requires kids to closely observe what happens to the bottle.

How is the bottle changing shape? What made it change its shape? Does it continue to crush when we add more ice water?

Building observation skills is foundational to future learning!

More experiments about air pressure to try out with your child

• Blast Off! A chemical reaction rocket
• The Science Behind the Floating Candle Trick
• H2-Oh My! A holey bottle that will not leak!