Banana Hammer – the science behind

News Hour:

You’ve heard of a banana lounge, but the banana hammer? Our friends at UNSW Science explore the science behind the fruit tool you won’t find at Bunnings.

Materials:

• 2 Bananas
• balsa wood board
• a nail
• Liquid Nitrogen
• cryo gloves
• crucible tongs

Key points:

• A banana is mostly made of water. Water is a liquid.
• The room temperature banana is too soft and mushy to hammer in a nail. Imagine trying to hammer in a nail with a water balloon.
• Freezing the water in the banana is one way to make it a better hammer.
• The water molecules in the banana start to slow down when you make them cold.
• They start holding onto each other more tightly, like the volunteers in the earlier demo.
• When the molecules get cold enough, the water in the banana becomes a solid (ice).
• With a frozen banana, the nail can easily be hammered because the solid water is much more rigid and tough than the liquid.

Warnings:

• DO NOT reach into the LN₂ with the cryo gloves. The LN₂ soaks into the gloves right away and traps it near your hand.
• Use the crucible tongs to fish the banana out of the LN₂ (it sinks to the bottom).
• Always use the cryo gloves when handling the frozen banana (or pieces of it, if it breaks up)
• The banana may break when hammering in the nail if it was left in the LN₂ too long. About 30 seconds to a minute is a good amount of time.
• Make sure the kids don’t grab pieces of banana. It stays cold for a long time, and will hurt their hands.