Algodoo

It uses the highly compressible Phun water to simulate real-life air to moderate accuracy. You can attach objects to the red block, or just drive vehicles right in. Objects on the red block can be raised or lowered with UP and DOWN arrows, and they can be rotated with LEFT and RIGHT arrows.

Included are a car with a spoiler and a number of interesting objects/shapes to play with. Control the car with ASD.