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