Your Classroom Becomes a Curling Rink!? Experience ‘Zero Friction’ Physics with Dry Ice (The Law of Inertia)

I’m Ken Kuwako, your Science Trainer. Every Day is an Experiment!

What would happen to objects if friction suddenly vanished from the world? You’ve learned about the Law of Inertia in your textbooks: an object will continue to move in a straight line at a constant speed unless acted upon by a net external force. But actually experiencing this is surprisingly difficult. Why? Because the annoying force of “friction” is always there on Earth to spoil the fun.Usually, schools use special gliding surfaces in the classroom. However, students often feel like this is just a “special laboratory event.” Plus, equipping every student group with expensive apparatus is a realistic budget constraint. That’s why I highly recommend an experiment using dry ice. Yes, that dry ice you get from the supermarket or bakery can become a magical item that turns physics concepts on their head!

Why Dry Ice Becomes a ‘Hovercraft’

Dry ice is simply carbon dioxide that has been cooled and solidified. When exposed to a room-temperature environment, it doesn’t melt into a liquid; it turns directly into a gas—a phenomenon called sublimation. So, what exactly is happening between the dry ice and the desk surface? The carbon dioxide gas rapidly blowing out from the bottom of the dry ice creates a thin layer of gas between the ice and the desk.In essence, the dry ice is slightly levitating on a cushion of its own gas. This is the exact same principle as a hovercraft, which floats and moves forward using air power.Because it’s floating, the friction with the desk is reduced to an absolute minimum. The sight of it gliding smoothly with just a light push of a finger, almost like it’s in a zero-gravity environment, is truly awe-inspiring. Today, let’s use this phenomenon to learn about uniform linear motion (constant velocity) while having a blast!

The Science Recipe

What you need: About $1 \text{ kg}$ of dry ice, one iPad per group.Tip: You might want to check for local ice dealers for the dry ice. I personally rely on Asahi Ice Industry, Inc. (http://www.icenet.or.jp/asahi/). They are an old-school ice supplier where you can buy dry ice starting from $1 \text{ kg}$ for about 500 yen. These days, you can even purchase it on Amazon.【Teacher’s Memo】 Even when stored in a freezer, $1 \text{ kg}$ of dry ice will sublimate (disappear) in about two days. The trick is to arrange delivery on a day when you have multiple classes scheduled.

The Experiment: Experience a Zero-Friction World

① Smash the dry ice into cubes about $5 \text{ cm}$ on a side (use a hammer to break it up) and distribute them to each group. The shape doesn’t need to be perfect.② Try sliding it across a level desk. 【Insider Tip】 If you can, spray the bottom surface of the dry ice with ethyl alcohol to dampen it before starting. This makes it glide even more smoothly because alcohol is less likely to freeze, creating a slicker membrane.

Swoosh…

Super-swoosh!

Be sure to watch the video for the actual motion. It slides so satisfyingly!https://youtu.be/SKrau9Jmsms?si=RfWwG2CPO04g_joJ③ Let’s leverage modern technology. Use an iPad and a stop-motion app to record the movement.The following photos were taken by students themselves. Since the object appears at equal intervals in the photos, it is clear at a glance that the speed is constant (uniform) and it is moving in a straight line (linear).

Bonus Fun: Dry Ice Curling!

After learning, let’s find the science in play. It would be a waste to only use the dry ice for one experiment! Let’s turn the classroom into a curling rink.What you need:Dry ice, vinyl tape, hammer, work glovesInstructions:① Stick vinyl tape on the desk to create a target. This will serve as the “house” (the circles in curling).

Make sure to mark a starting line, too.

② Break the dry ice into a manageable size using a hammer.【Safety Warning】 Always wear work gloves when handling dry ice. It is extremely cold, $-79^\circ \text{C}$, and touching it with bare skin can cause frostbite. Adults must supervise children during this process.③ Put on the gloves and slide the dry ice from the starting line. Score 100 points for landing inside the innermost circle (the red tape) and 50 points for the outer circle. Each person gets five slides, and the highest total score wins.With just a slight variation in the force you apply, the dry ice will either overshoot or fall short. You’ll be able to feel the interplay between inertia and the minimal friction firsthand!

Inquiries and Requests

Make the wonders and fun of science more accessible! I have compiled easy-to-understand guides on fun science experiments you can do at home, along with tips and tricks. Feel free to search around!The content from Kagaku no Netachō (The Science Handbook) is now a book. Learn more here.About the administrator, Ken Kuwako, click here.For various requests (writing, lectures, experiment workshops, TV supervision, appearances, etc.), click here.Article updates are posted on X (formerly Twitter)!

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