News and Views

I have a nice insulated coffee cup that has a screw-on cap with a rubber O-ring seal. Putting the cap on has been very frustrating for me over the two years I have owned it. Sometimes I gently screw the cap on, and the seal is good, no coffee leaks. Other times no matter how hard I twist it on, the lid leaks. I can remove and replace it several times, and it still leaks. I thought the problem had gone away around last April, but it came back again a couple of months ago.

I have been putting up with this all this time, and then the other day I happened to remember the Space Shuttle Challenger disaster, and a simple demonstration that Richard Feymann did to show what had caused it. He placed a piece of the shuttle O-ring into a glass of ice water and when he pulled it out, the O-ring was brittle and hard. The cold morning of the Challenger flight had made the O-rings inflexible, thus allowing gases to leak and ignite, causing the explosion.

The same thing was happening to my coffee cup. If the lid (and O-ring) was warm, which usually was the case in the summer, the seal was good. But on these cold winter mornings the O-ring is inflexible and doesn’t seal well. I’ve gone to running hot water over the lid, especially over the O-ring, and now I get a good seal every time.

Physics at work in every day life!