Two syringes, one squashes

By the end you can say what is between the particles of a gas, and why the same push does almost nothing to water.

A very common way to think about this

“Stuff is solid all the way through. There is no gap inside air — air is just thin stuff, and if you squash it, you squash the stuff itself.”

Nothing you can see has visible holes in it. Water looks like water everywhere you cut it, and air looks like nothing at all, so an empty gap between invisible pieces is a strange thing to invent.

1. Predict first

Both syringes are sealed with 20 mL inside — one of air, one of water. You lean on both plungers just as hard. What happens?

2. Try it

What is sealed inside the syringe — The same push shrinks the air to a fraction of its volume and moves the water by almost nothing at all.
How hard you press the plunger (0–120 N) — Air keeps giving as you press harder, and it springs straight back — nothing was pushed out and nothing was crushed.

One syringe at a time. Note the reading, then swap and press just as hard.

Volume20.0 mL

Of its start100.0 %

Pressure inside101.3 kPa

Sealed inside the syringe

Push on the plunger0 N

3. The check

Keep experimenting above. This question opens once you have seen the thing it asks about.

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