Describe how and why air density changes with changes in altitude. - ANSWER- Air density decreases with an increase in altitude because air particles have mass and are pulled down by Earth's gravity. 

Density is defined as - ANSWER- mass divided by volume. 

Nitrogen is about _____ of the Earths atmosphere - ANSWER- 78% 

A mechanical wave cannot travel through a - ANSWER- vacuum. 

In which layer is the ozone layer located? - ANSWER- Stratosphere 

Where does Earth's weather happen? - ANSWER- Troposphere 

The troposphere is - ANSWER- the densest of the atmospheric layers. 

The exosphere is the least - ANSWER- dense atmospheric layer.