Dear Tom,

I visited Pikes Peak in Colorado recently and wondered why is it always colder up there than down in Denver.

—George Carvarelli, Chicago

Dear George,

Temperature is a measure of the average speed at which the molecules of a substance are vibrating. The faster the vibration, the higher the temperature. Air pressure is the weight of the atmosphere above you, but as you go higher, air pressure decreases. But as air pressure decreases, the space between air molecules expands and the expansion removes some of the energy of the moving molecules, causing them to slow down. The result is a drop in temperature. For this reason, the temp at Pikes Peak, at an elevation of 14,115 feet, will be lower than the temperature at lower elevations, like Denver (5,280 feet).