# Atmospheric reentry drag and friction

What is the difference of air drag in ground level with let say moderate speeds like fast cars 200km/h to 400km/h with high speed vehicle reentry at high altitude where the air is so rarified. Making more simple is: {Low speed ( up to 0.5 mach ) + ground level air pressure )} ****versus**** { High speed ( 6- 7 km/s + air density at Kármán line.

## 1 Answer

Drag has a lot of more complex factors that would require some simulation to determine exact values, but the simplification that is often used shows drag increasing linearly with air density and with the square of velocity.

Density at the Karman line is 1/2,200,000 that of ground level, so an increase from 0.5 mach to 7 km/s will feel roughly $$\frac{(7000/170)^2}{2200000}=0.00077$$ times the amount of drag. So, the same object in LEO would feel less than 1 tenth of 1 percent of the drag of the same object speeding along the ground.

However, this is still a significant amount of drag and you'll find yourself falling out of orbit pretty quickly.