Quick Temperature versus Air Pressure Experiment

The other day my two daughters completed a very simple science experiment without even knowing it!  My wife and I were working on making dinner and both of our daughters went outside to the backyard to play.  The brought with them a large plastic ball filled with air and were kicking it around for about 45 minutes.  When it was time to come in for dinner, they noticed that the ball appeared to have less air in it and asked if it was leaking.

So what happened?  Was it a leak?  Nope, no leaks.  The ball was outside long enough and the temperature was low enough outside that the air temperature inside the ball dropped quite a bit.  When air temperature drops, the particles in the air move around more slowly and bounce against the sides of the ball wall less frequently.  This results in a drop in air pressure inside the ball and thus explains why the ball appears to have lost air, as shown above.  

Once the ball was brought inside it only took a couple of minutes for the air temperature to increase and for the ball to "re-inflate".  No air was added to the ball, but as the air particles inside gained speed, the inside air pressure increased.  

Very cool!  This just goes to show you that science surrounds you and is easy to find if you just take a moment to stop and look for it.