What changes air density

1Change the atmosphere

2Observe the air density Conceptual Illustration — Not to Scale

Standard Sea-Level Air
Air Under Current Conditions
Same-size boxes. dry air (nitrogen, oxygen)  water vapor, lighter  leaving the box

3Pressure altitude and density altitude

Pressure altitude
0 ft
Density altitude
0 ft
the altitude the airplane performs like

4What it means for takeoff

Cessna 172N — Takeoff Ground Roll

Source: Cessna 172N POH

Standard sea level
805 ft
Selected conditions
805 ft
Additional roll
0 ft