Fun with Marshmallows Science Project on Density



This is one of the more unique science experiments for kids that is designed to teach students about density. Ideally, this is one of those science projects that is done by students in grades 3rd – 5th.


Materials Needed

  • Mini Marshmallows
  • Bowl with Water
  • Bowl with Cooking Oil
  • Cornstarch
  • Cutting Board
  • Spoon




Have several marshmallows ready to go. You’ll want at least six whole marshmallows from the bag, and three that are cut in half with the spoon. If you are doing this as one of the science projects for teachers on the website, you can give each student eight total mini marshmallow and they will have plenty for the experiment.


Project Day

Take your first whole marshmallow and place it in the water. Does it sink or is it floating? Record your results.

Now, take one of the half marshmallows and place it in the water. Does this one with the exposed inside float?

Place some cornstarch on your cutting board and smash a marshmallow into it with the spoon. Place this into the water. Does it sink? How about if you only partially smash a marshmallow, will it sink all the way too?

Next, take a marshmallow and place it into the cooking oil. What happened? Try mashing up the marshmallow, did your results change? How about with the speed of the results?


So What Just Happened?

Thanks to the design of the marshmallow, when it is whole, it will float at the top. That is because the sugary surface of the marshmallow covers a wide area. As you compact the sugar, the area becomes denser. This allows less water to get into the dense material, and that causes it to sink. The more you squash the marshmallow, the lower and faster it will sink.

In the oil, you have a substance that is denser than the marshmallow. So whether the marshmallow was whole, or mashed up, it still sinks into the oil. Once you’re done, you can eat up the rest of the marshmallows in your hand and consider this one of the tastiest science projects for kids around.




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