Compressing Solids, Liquids and Gases
Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required
Categories: Particles and States of Matter, Pressure and Fluids
Alternative titles: Compressibility of Matter
Summary
This demonstration uses syringes filled with air, water, and solid pellets to show that gases are compressible while liquids and solids are not. It models how the spacing between particles differs among solids, liquids, and gases.
Procedure
Obtain three large syringes (50-100mL recommended). Leave one empty (air), fill one with water, and use one prefilled with small plastic pellets to represent a solid.
For the syringe containing air: pull back the plunger to draw in air, seal the nozzle tightly with a thumb or a rubber eraser, and then push the plunger to feel the compression of the gas.
For the syringe containing water: fill the syringe completely with water, remove all air bubbles, seal the nozzle, and then attempt to compress the water by pushing on the plunger.
For the syringe containing plastic pellets: use a syringe half-filled with pellets, seal the nozzle, and try pushing the plunger to see whether the solid can be compressed.
Compare how much the plunger moves in each case and discuss what this indicates about the spacing of particles in solids, liquids, and gases.
Links
Variations
Use different liquids (e.g., oil or glycerin) to test if all liquids are equally incompressible.
Try syringes of different sizes to compare the volume change in gases.
Perform the gas step using a pressure gauge attachment to measure the air compression quantitatively.
Use a transparent syringe and film the plunger motion for comparison.
Safety Precautions
Wear safety glasses to prevent splashes during the water step.
Do not point filled syringes toward anyone; pressure may cause contents to eject suddenly.
Ensure tight seals only with appropriate force; do not overstress or crack the syringes.
Questions to Consider
Which state of matter was easiest to compress? (The gas.)
Which states of matter were hardest to compress? (The solid and the liquid.)
What does the ease of compression tell us about particle spacing in gases, liquids, and solids? (Gases have widely spaced particles, while liquids and solids have particles close together.)
Why do liquids flow but solids do not, even though both are nearly incompressible? (In liquids, particles can move around each other; in solids, they are locked in fixed positions.)
How does this experiment support the particle model of matter? (It provides evidence that different states of matter differ in particle arrangement and movement, explaining compressibility.)