Q1.
What do you observe?
Answer
Four things, in this order:
- With your thumb sealing the open end, the plunger can be pushed inwards — the volume of air inside the syringe decreases, even though no air is getting out.
- It gets harder to push as you go. The air resists more and more.
- The moment you stop pushing, the plunger moves back to its original position by itself.
- Do the whole thing again with water in the syringe instead of air, and the plunger barely moves at all — water is practically incompressible.
Why the two behave so differently: in a gas the interparticle spacing is maximum, so pushing simply brings the particles closer and the gas takes up less room. In a liquid the particles are already close together, so there is almost no spare space left to squeeze out.