Small pieces of chalk, when frozen in liquid nitrogen, release nitrogen gas as they warm. This escaping gas forms a cushion between the chalk and the floor, causing the chalk to hover and slide across smooth surfaces.

1. Break chalk into small pieces.
2. Place the chalk pieces into a container of liquid nitrogen until thoroughly cooled.
3. Using insulated gloves and tongs, remove a piece of frozen chalk.
4. Immediately set the chalk onto a smooth, hard surface such as hardwood or linoleum flooring.
5. Observe as the chalk glides and hovers on a thin cushion of rapidly escaping nitrogen gas.
6. Repeat with additional pieces to show consistency of the effect.

Hovercraft chalk - J Rhee:

📄 Things to Do with Liquid Nitrogen (activity 4.) - Thought Co: https://www.thoughtco.com/liquid-nitrogen-activities-and-projects-603678

• Try different materials (erasers, coins, or small stones) to compare how they behave after immersion in liquid nitrogen.
• Place the chalk on slightly inclined surfaces to make it “drive” in one direction.

• Safety glasses required.
• Wear cryogenic gloves when handling liquid nitrogen.
• Use tongs to remove chalk from liquid nitrogen.
• Only perform on sturdy, non-fragile surfaces that won’t crack from the cold.
• Avoid touching frozen chalk directly, as it may cause frostbite.
• Ensure good ventilation to avoid nitrogen buildup.

• Why does the chalk glide instead of sticking to the floor?
• What role does the escaping nitrogen gas play in this demonstration?
• How is this effect similar to a hovercraft or an air hockey table?
• Would the effect be stronger or weaker on a rough surface compared to a smooth one?
• What does this tell us about friction and lubrication?