On May 4th, 2016, graduate students from the Marohn laboratory brought liquid nitrogen to Caroline Elementary School for various scientific activities and demonstrations. The goal of this outreach was to help fifth graders understand the physical properties of liquid nitrogen (liquid phase, cold -321 ∘ F), and phase changes. Our activities included
- We deflated air balloons with liquid nitrogen, and stuffed many of them into a small container. Then, we took the balloons out one by one and let them deflate at room temperature and asked the students to explain what they saw. We then re-froze one of the balloons to show that the gases inside the balloon actually liquified.
- We froze a few pennies in liquid nitrogen — some old and some new. We asked the students what they expected to see when the coins were frozen. We took the pennies out and smashed them with a hammer to demonstrate that metal became brittle when cold. The new pennies shattered easily while the older one only bent a little. We asked the students to deduce something about the pennies from what they saw. We explained that the different behaviors resulted from differences in the material composition of the pennies — the newer coins (after 1982) were made of zinc and coated with a thin layer of copper while the older coins were made entirely of copper.
- In another activity, we froze a banana in liquid nitrogen and tried to use it to smash a pile of frozen coins. The banana was shattered while the coins remained intact. We explained that the frozen banana was more fragile because of its high water and sugar content.
- In our last activity, we let the students freeze a few marshmallows in liquid nitrogen. We then let them eat this frozen treat! It did not hurt; rather, they found it tasty and cold like ice-cream. Some students were able to breathe out foggy smoke through their nose. Very cool.
These activities were repeated for two classes of fifth graders and they all enjoyed it. Some students demonstrated quite a bit of prior knowledge (‘I saw it in a Youtube video before’) and a great affinity for science through their clear explanations and keen observations. In an unofficial vote, our activities were found to be the coolest the students had experienced yet in their fifth grade science class.
Fig 1: Balloons taken out of liquid nitrogen re-inflate by themselves.
Fig 2: Marshmallows frozen with liquid nitrogen.
Fig 3: Fifth-graders watching the liquid nitrogen demonstration.