(20 14? Nanning) As shown in the picture, Xiao Ming made a device for measuring wind speed. When the wind blows over the probe, the air velocity on the upper and lower surfaces of the probe is different.
(1) As shown in the figure, when the wind blows over the probe, because the upper surface of the probe is convex, the distance of air passing through the upper surface is longer than that of the lower surface, and the speed of air passing through the upper surface is faster than that of the lower surface, so the pressure of air on the lower surface of the probe is greater;
(2) When the wind speed decreases, the slider P moves downward under the action of the spring; If the voltmeter is converted into an instrument for measuring wind speed, it is required that the indicated voltage value will increase when the wind speed increases, so the voltmeter should be connected in parallel at both ends of the sliding rheostat R 1, so that when the wind speed increases, the slider will move up, the resistance of the rheostat will increase, the partial pressure will increase and the indicated value will increase.
So, the answer is: big; Downward; R 1。