Answer:
increase the pressure
Explanation:
There is a fixed number of molecules of air inside of the syringe. When the plunger is pushed in, these molecules begin to push (or collide) against each other and the sides of the syringe more and more because of the lack of space. This decrease in volume (less space) increases the pressure (more collisions). The opposite phenomenon occurs when the plunger is pulled out. Both occurrences are a demonstration of Boyle's Law.
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