Wuxi tomorrow air pressure

(1) The length of the syringe should be measured in the experiment, so besides the syringe, spring dynamometer, string, rubber cap and water, there should be a scale.

(2) As can be seen from the figure, the volume of the syringe is 2.5 ml, that is, 2.5 cubic centimeters ... The length of all scales of the syringe L=4cm, because the syringe is a cylinder, according to its volume product, S=VL=2.5cm34cm=0.625cm2.

In the experiment, the piston was pushed to the bottom of the syringe barrel to exhaust the air in the syringe. The index f of the spring dynamometer is F=7.5N, which is the pressure of the atmosphere on the piston. Substitute it into the formula.

p = FS = 7.5n 0.625× 10-4 m2 = 1.2× 105 pa；

(3) If the piston is not completely sealed with the syringe barrel wall, the air in the syringe barrel will reduce the tension, and the measured atmospheric pressure will be smaller under the condition of constant area; If the indicator reading of the spring dynamometer is incorrect, the measured value will be less than the real value and greater than the real value, so B.

(4) If there is friction between the piston and the inner wall of the syringe, when the syringe is balanced under the pulling force F, the pulling force F is greater than the pressure of the atmosphere on the piston, which makes the measured value larger. So Xiaohong's experimental steps are to reduce the influence of friction on the experimental results.

So the answer is: (1) scale;

(2)0.625; The atmospheric pressure calculated from the experimental data is1.2×105 pa;

(3)B；

(4) Reduce the influence of friction on the experimental results.