What's the air pressure in Nantong, Jiangsu today?

(1) During the experiment, the piston was pushed to the bottom of the syringe barrel to exhaust the air in the syringe.

(2) When the piston in the syringe begins to slide, the tension of the spring dynamometer just balances with the atmospheric pressure, so it is necessary to record instructions at this time;

The syringe is a cylinder, so it is necessary to measure the length of its scale part, and then read out the empty product V to get the area of the piston S=VL. Substitute the measurement results into the pressure formula, P = fs = FVL = FLV.

(3) If the air in the cylinder is not exhausted, the measured value of tensile force will be very small, which leads to the measured atmospheric pressure value being very small according to the formula P=FS; On the contrary, if the friction between the piston and the inner wall of the syringe is large, the measured value of tension will be too large, resulting in the measured atmospheric pressure value being too large.

(4) Because of the two injectors A and B, the cross-sectional area of the piston is 0.5cm2 and 2cm2, respectively.

When the atmospheric pressure is about 100000Pa and the area is 2cm2, that is, 0.0002m2,

From P=FS, we can get f = ps =100000pa× 0.0002m2 = 20n.

Because that known range of the spr dynamometer is 10N, which exceeds the range of the dynamometer,

So we have to use syringes in the experiment.

So the reason is that the force required to pull the syringe B is beyond the range of the spring dynamometer.

So the answer is: (1) exhaust the air in the cylinder and seal the syringe;

②FLV。

(3) small

(4) a; The force required to pull syringe B is beyond the range of the spring dynamometer.