There was no additional air in the tire the second time Lawrence checked the air pressure, but something did change between the two measurements. The tires had rolled over 10 miles of road on the trip to school. Any time one surface moves over another, it causes friction. Friction is a force that opposes the motion of two surfaces that are touching, and friction between two surfaces always generates heat. Quickly rub your hands together and you’ll feel the heat generated by the friction between them. As the tires moved over the road, friction between the tires and road generated heat. In short, the tires got warmer and so did the air inside them.
Beth was blowing up the kiddie pool for tomorrows party. It was hot outside this afternoon so she was glad when the pool was fully inflated and she could go inside. The next morning when she went outside to put water in the pool she was surprised to see that the pool was no longer fully inflated. She checked but there were no leaks so she added some more air before filling it with water.
Was it hotter outside in the afternoon or morning?