Learn How Engines Work with a Shocking “Pop!” — The Secret of Alcohol Explosion Experiments (First Law of Thermodynamics)

I am Ken Kuwako, your Science Trainer. Every day is an experiment.

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The “Pop!” That Opens the Door to Science: A Safe At-Home Thermodynamics Experiment

【This article is also available on Radio!】

There is something instinctively thrilling about seeing something launch right before your eyes. Have you ever looked at a simple everyday object and wondered, “How does that actually work?”

Today, I want to share a thrilling yet safe science experiment to spark your intellectual curiosity. The star of the show? Hand sanitizer (rubbing alcohol), something found in almost every household. It is the magic key to unlocking a powerful, invisible force.

The word “explosion” might sound a bit intense, but don’t worry. This experiment simply harnesses the power of a tiny amount of alcohol turning into gas and rapidly expanding. You will get to hear, see, and feel “gas doing work” in real-time. This phenomenon is the gateway to the profound world of thermodynamics—the same principles that power car engines and launch rockets into space.

Join me as we experience this surprising “Pop!” and rediscover the joy of science!

This experiment isn’t just a great way for middle schoolers to understand the difference between “combustion” and “explosions”; it is also the perfect visual aid for grasping the “First Law of Thermodynamics,” which is often a hurdle in high school physics.

The Science Recipe: Try the Alcohol Explosion Experiment!

The heart of this experiment lies in the fact that burning a small amount of alcohol instantly heats and expands the air inside a sealed can. This trapped energy, looking for an escape, provides the power to launch a paper cup lid high into the air.

What You Will Need

• Paper Cup: Acts as your lid (the projectile). A standard size is perfect.
• Aluminum Can: An empty soda can works best. One with a flat bottom is more stable.
• Can Opener: To remove the top of the aluminum can.
• Awl (or a sharp tool): To poke a small ignition hole in the bottom of the can.
• Rubbing Alcohol: Ethanol with a concentration of 70% or higher. Spray types are highly recommended as they mist easily.
• Lighter or Multi-purpose Lighter: For ignition.
• Safety Gear: Always have a wet cloth and a bucket of water ready.

Experimental Procedure: Safety First!

Once you are ready, let’s start. Precision and care with each step are the secrets to both success and safety.

1. Cut the top off the can Use the can opener to completely remove the top (the drinking side) of the aluminum can. Be careful not to cut your hands on the sharp edges. Wash and dry the inside thoroughly.
2. Create the ignition hole Using the awl, poke a tiny hole in the center of the bottom of the can. This will be your “fire gateway.” Work on a stable surface and be careful not to slip.
3. Add the alcohol (Most Important Step!) Spray just 2 pumps or add 2-3 drops of alcohol into the can. NEVER add more than this. Too much alcohol can cause a large flame to linger after the explosion, which is dangerous. This “tiny amount” is what creates the perfect scientific reaction.
4. Vaporize and mix Place the paper cup lightly on top of the can. Give the can a few gentle shakes to help the alcohol evaporate and distribute the vapor throughout the can.
5. The Moment of Ignition! Double-check that your wet cloth and water bucket are within reach. Bring the lighter flame close to the hole at the bottom.

Results: The “Pop” is Thermodynamics in Action

https://youtu.be/mTNW7m13Eyc

The moment you bring the flame close, you’ll hear a satisfying “Pop!” and the paper cup will soar! This happens because the alcohol vapor burns instantly, causing the air temperature inside to skyrocket. This hot air wants to expand aggressively, and that force pushes the paper cup toward the ceiling.

This is a real-world experience of the First Law of Thermodynamics. The “chemical energy” of the alcohol converted into “thermal energy” via combustion. That heat then performed “work” by pushing the gas, which finally became the “kinetic energy” that launched the cup. Energy is constantly shifting forms, dancing right before your eyes.

We captured this heat movement with a thermographic camera. Look at these incredible results:

Just before ignition.

At the moment of the “Pop!”, the internal temperature spikes into the red!

【WARNING!】 Never look directly into the can from above during the experiment. It is extremely dangerous.

【Golden Rules for a Safe Experiment】

• No Overdosing!: Limit the alcohol to 2 pumps. Being greedy with the amount can lead to a sustained fire inside the can. If a flame persists, cover it with a wet cloth to cut off the oxygen and extinguish it calmly.
• Adult Supervision Required: This experiment deals with the “power” of science. Students should always perform this with a parent, guardian, or teacher in a clear area away from flammable materials.
• Ventilation is Key: The air after the experiment contains combustion gases. Open a window and ensure good airflow.

For those who want to dive deeper into these thermodynamic wonders or revisit high school physics, my book “High School Physics Review for Adults” offers even more fun and detailed explanations. Give it a read, and you’ll find that the invisible flow of energy feels much more familiar.

A dynamic world of science is hiding in your kitchen cabinets. Are you ready to be amazed by the “work of gas” taught by just a few drops of alcohol? Stay safe and give it a try!

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