9.17 Atmospheric air is drawn into a low-speed wind tunnel where a 30 cm diameter sphere is mounted on a force balance to measure drag. The oil-filled manometer used to measure the static pressure inside the tunnel reads −40 mm of oil and the oil has a specific gravity of 0.85. Determine the air speed in the tunnel and the drag force on the sphere. Determine the drag force when the air speed is reduced to a manometer reading of −20 mm of oil.