A marshmallow inside a syringe expands when the plunger is pulled out (lowering pressure) and shrinks when the plunger is pushed in (raising pressure). This demonstrates Boyle’s Law: pressure and volume are inversely related.

1. (Optional) Draw a face on a miniature marshmallow with a felt-tip pen.
2. Remove the plunger from a 50mL or bigger plastic syringe.
3. Place the marshmallow inside the syringe barrel.
4. Replace the plunger.
5. Seal the syringe tip with a cap or a finger.
6. Pull the plunger outward to decrease pressure inside the syringe. Observe the marshmallow expand.
7. Push the plunger inward to increase pressure inside the syringe. Observe the marshmallow shrink.

Marshmallow in a syringe demo - Laura Crain:

Marshmallow in a Vacuum - FlinnScientific:

📄 The Expanding Marshmallow - Flinn Scientific: https://www.flinnsci.com/api/library/Download/87df044174b24fe38b73cd2a96386f15

• Try using different sizes of marshmallows.
• Compare fresh versus stale marshmallows (fresh ones expand more due to more trapped air).
• Use different syringe sizes to test the effect of chamber volume.

• Follow standard laboratory safety procedures.
• Do not eat marshmallows used in the experiment.

• What happens to the volume of the marshmallow when pressure decreases? (It increases due to expansion of trapped air bubbles.)
• Why does the marshmallow shrink when the plunger is pushed in? (Increased pressure compresses the air bubbles inside.)
• How does this experiment illustrate Boyle’s Law? (It shows the inverse relationship between pressure and volume: when one goes down, the other goes up.)
• What role do the air bubbles inside the marshmallow play in this demonstration? (They act like tiny balloons that expand or contract depending on external pressure.)