Answer:
If the syringes and tubes are filled with air instead of water, the difference would be mainly due to the difference in the properties of air and water. Air is a compressible gas, while water is an incompressible liquid. This would result in a different behavior of the fluid when being pushed through the system.
When the syringe plunger is pushed to force air through the tube, the air molecules will begin to compress, decreasing the distance between them. This will cause an increase in pressure within the tube that can be measured using the pressure gauge. However, this pressure will not remain constant as the air continues to compress, making the measured pressure unreliable.
On the other hand, when the syringe plunger is pushed to force water through the tube, the water molecules will not compress. Therefore, the increase in pressure within the tube will be directly proportional to the force applied to the syringe plunger, resulting in an accurate measurement of pressure.
In summary, if the syringes and tube are filled with air instead of water, the difference would be that the measured pressure would not be reliable due to the compressibility of air.