2. The balloon trick

This experiment is designed to show how the volume of a gas expands as it warms, and contracts as it cools. The method: Blow up balloons in warm air, then expose them to cold air and they will deflate. They will reinflate when you return them to warm air.

This is the same reason car tires deflate in cold weather, said Michael Kennedy, a research professor and director of Northwestern University’s Science in Society, a science education center.

We inflated half a dozen balloons inside, then bundled up and went outside to wait for them to shrink in the minus 39 degree windchill. And we waited. Gus and Eren decided to bury their balloons in a snow bank. Hildy’s flew into the street.

When we could no longer feel our noses, we put the remaining balloons in a bag, tied it to the door handle, and rushed inside. After about 45 minutes, the balloons had deflated only slightly and we realized we hadn’t been very scientific: It might have been wise to first measure the balloons’ original circumference, for example.

Image Alex, the lab assistant, prepared the balloon experiment for the scientists. Credit... Danielle Scruggs for The New York Times

Once back inside, the balloons did return to their previous shape, but by this time only the adults cared. The child scientists wanted more Sprite slushies.