demonstrations:liquid_nitrogen_banana_hammer

Liquid Nitrogen Banana Hammer

Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff

Categories: Liquid Nitrogen

Alternative titles: Cryogenic Banana Hammer

Summary

A banana frozen in liquid nitrogen becomes so hard that it can be used like a hammer to drive a nail into wood.

Procedure

  1. Put on safety glasses and cryogenic gloves.
  2. Place a banana into a container of liquid nitrogen and allow it to freeze solid.
  3. Using tongs, remove the frozen banana from the liquid nitrogen.
  4. Hold the banana firmly and attempt to hammer a nail into a piece of soft wood.
  5. Observe that the banana is hard enough to act like a hammer.

The banana hammer experiment - BOC South Pacific:


Variations

  • Try freezing other fruits or vegetables (carrots, cucumbers, or apples) and test their hardness.
  • Compare how a fresh banana bends versus how a frozen banana shatters when struck.

Safety Precautions

  • Safety glasses required.
  • Wear cryogenic gloves when handling liquid nitrogen and the frozen banana.
  • Use tongs to place and remove the banana from liquid nitrogen.
  • Do not eat the banana (ingesting liquid nitrogen can be fatal).
  • Only hammer into soft wood to prevent splinters or shattering of the banana.
  • Ensure demonstration area is dry and non-slippery, as nitrogen fog can create condensation.

Questions to Consider

  • Why does a banana, normally soft, become hard enough to hammer a nail?
  • How does liquid nitrogen change the physical properties of organic materials?
  • What happens at the molecular level when water inside the banana freezes so quickly?
  • Why does the frozen banana shatter more easily compared to a fresh one?
  • How could this principle be applied in real-world material testing or engineering?