Marshmallow Squisher!

Curriculum links:

• Physics – Boyle’s law – Relationship between pressure and volume at constant temperature

Learning objectives:

1. Understand the effects of pressure
2. Use mechanical devices to use air pressure to change the volume of materials

Materials:

• Marshmallows
• A Bottle that was used for a fizzy drink
• Air pump (e.g. a bike pump)

Safety:

• Make sure to only use bottles that have had fizzy drinks in them before. They have been designed to withstand pressure!
• Wear safety goggles.

Instructions:

• Put the marshmallows into the bottle and fill them up to at least ¾ the way. Use marshmallows that will just fit inside the neck of the bottle but don’t cut or tear the marshmallows as they will stick to the side of the bottle.
• Attached the air pump to the top of the bottle and start adding air. This will increase pressure and you should see the marshmallows decrease in size.
• When you’re ready, slowly release the pressure and allow for the air to come out. The marshmallows with regain their original size.

How it works:

Marshmallows are made of sugar and air. They are used to demonstrate how pressure and volume are inversely proportional to each other. That means that when the pressure goes up then the volume goes down.

The marshmallow shrinks when you add air inside but then regains its original size when you release the top. The structure of a marshmallow is such that there are many bubbles of air trapped by sugar molecules. There is a fixed number of air molecules inside the marshmallow.

As the air is pushed in, the pressure inside the bottle increases and the bubbles of air decrease in size, therefore the volume of the marshmallow decreases. Exactly the opposite then occurs when the top is opened again.