Pumping Up for a Ride
Here's a simple experiment to try while tuning up your bike for the Friday afternoon Refugio Ridge Ride over the mountains and to the beach. Pump up your bike tire with a hand pump and feel the bottom of the pump. It will be hot. Now wait a moment and release the pump (and a puff of air) from the tire and quickly feel the valve stem on the tire. It should feel cool. Can you explain these different results? Isn't it the same air in each case? Hint: It's not friction that makes it so hard to pump up a tire with a hand pump!
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