If you stick your hand out of the window of a moving car you can explore the properties of “air drag.” The faster you go, the stronger the force. If your palm is facing up or down the drag is much smaller than when your palm faces forward or backward, showing that the shape of the object matters. A smaller hand experiences less drag than a larger one. So, drag depends on velocity, area, shape, and the density of the air. These properties are different from other contact friction forces, but the force is still exerted in the direction opposite motion, so it slows down the object. Liquids exert similar, but stronger, drag forces.