Vacuum Jar Marshmallow: The Expanding Sweet Surprise
Place marshmallows inside a vacuum jar and watch them magically grow bigger — a fun and unforgettable way to explore air pressure and gases!
Overview
The Vacuum Jar Marshmallow activity is a simple but fascinating science experiment that helps children understand the concept of air pressure. At first glance, marshmallows may look soft and solid, but they actually contain thousands of tiny trapped air bubbles inside them.
When the marshmallow is placed inside a vacuum jar and the air is slowly removed, something amazing happens — the marshmallow expands and grows much larger than its normal size. When air is allowed back into the jar, it shrinks again.
This exciting visual effect makes invisible air pressure easy to understand. Instead of only learning from textbooks, students can directly observe how gases behave when pressure changes.
For younger children, the activity feels magical, almost like the marshmallow is “breathing.” For older students, it becomes a hands-on introduction to gas laws, pressure, and the relationship between pressure and volume.
The Vacuum Jar Marshmallow experiment is quick, engaging, and perfect for classrooms, science fairs, STEM clubs, or home science learning.
Time: 10–15 minutes
Complexity: Beginner
Setup: Vacuum jar marshmallow
Activity Materials Required
- Transparent vacuum jar or vacuum chamber
- Vacuum pump (manual or electric)
- 2–5 marshmallows
- Small tray or plate
- Adult supervision
- Notebook for observations (optional)
Step-by-Step Instructions
step1:Prepare the Marshmallows
Place a few marshmallows on a small tray or plate. Make sure they are separated slightly so students can observe each one clearly.
Step 2: Set Up the Vacuum Jar
Place the tray carefully inside the vacuum jar or chamber and close the lid tightly to create an airtight seal.
Step 3: Begin Removing the Air
Use the vacuum pump slowly to remove air from the chamber. Students should observe the marshmallows carefully during this step.
Step 4: Watch the Expansion
As air pressure inside the jar decreases, the marshmallows begin to puff up and grow larger. Some may even double in size.
Step 5: Observe Carefully
Ask students questions such as:
- Why are the marshmallows expanding?
- What might be happening inside them?
- Do all marshmallows expand equally?
Step 6: Release the Air
Slowly allow air back into the chamber. The marshmallows will shrink back close to their original size.
Step 7: Record Observations
Students can draw the marshmallows before and after the experiment and describe the changes they observed.
The Science Behind the Activity
Marshmallows are made with tiny pockets of trapped air. Normally, the air around us pushes on these air pockets from all directions. This pushing force is called air pressure.
When air is removed from the vacuum jar, the outside pressure decreases. Since there is now less pressure pushing inward, the trapped air inside the marshmallow expands outward, causing the marshmallow to grow bigger.
This Vacuum Jar Marshmallow experiment demonstrates the relationship between pressure and volume in gases.
P1 x V1 = P2 x V2
This is Boyle’s Law. It explains that when pressure decreases, volume increases, as long as temperature remains nearly constant.
The Vacuum Jar Marshmallow experiment also shows that gases take up more space when they are under lower pressure.
Scientists and engineers study these same principles in weather balloons, airplanes, submarines, and even space exploration.
Pro Tip
Try using:
- Mini marshmallows
- Colored marshmallows
- Foam candy
- A partially inflated balloon
Students can compare which object expands the most inside the vacuum jar.
For an extra fun challenge, ask students to predict what will happen before starting the experiment.
Expected Results
Students will observe that:
- Marshmallows grow larger when air is removed
- Marshmallows shrink when air returns
- Air occupies space
- Pressure changes can affect volume
Most children are surprised to discover that marshmallows contain so much trapped air.
By the end of the activity, students will better understand:
- Air pressure
- Gas expansion
- Boyle’s Law
- Scientific observation skills
The Vacuum Jar Marshmallow activity also encourages curiosity and prediction-making.
Conclusion
The Vacuum Jar Marshmallow experiment transforms an ordinary sweet into a powerful science demonstration. By watching marshmallows expand and shrink, students can actually see the effects of changing air pressure.
This simple Vacuum Jar Marshmallow hands-on activity makes invisible scientific concepts visible, memorable, and exciting. It helps children understand that science is not just something found in books — it can happen right in front of their eyes.
Sometimes, the best science lessons begin with a marshmallow.
Frequently Asked Questions
1. Why do marshmallows expand in the vacuum jar?
Marshmallows contain many tiny trapped air bubbles inside them. When the air pressure outside decreases in the vacuum jar, the trapped air expands and pushes outward, making the marshmallow grow bigger.
2. Why do marshmallows shrink again afterward?
When air is allowed back into the jar, the outside pressure increases again. This pressure compresses the air bubbles inside the marshmallow, causing it to shrink close to its original size.
3. Is the marshmallow filled with air?
Yes, marshmallows are actually a type of foam that contains thousands of tiny air pockets. These trapped air bubbles are what make marshmallows soft, light, and fluffy.
4. Does the marshmallow become lighter when it expands?
No, the marshmallow does not lose much mass during the experiment. Only its volume changes because the trapped air inside spreads out more under lower pressure.
5. Can this Vacuum Jar Marshmallow experiment work without a vacuum pump?
A large airtight syringe can create a small version of the effect, but a vacuum pump produces much clearer and more dramatic results. The stronger the pressure change, the better the expansion can be observed.
