Revisiting Scenario A
So let’s revisit Scenario A and try to visualize the air particles inside of the syringe at each step.
When we take off the blue cap and pull the plunger up to 35, air particles (represented by the 35 green dots) enter the syringe. When we put the blue cap back on, the syringe becomes a closed system and air particles can no longer get in or out. So when we push the plunger down to 20, there are still 35 green dots in the syringe. And when we release the plunger and it goes back up to 35, there are still 35 green dots in the syringe.