July Monthly Action Idea
Exploring Science and Math with Food!

Activity Idea: Finding the Speed of Light with Marshmallows
Source: Healthy Kids Challenge, Explore MyPlate with School Nutrition booklet
Description: Kids learn about physics through food science
Grade: 6-8
  • a microwave oven (the oven must be the type that has no mechanical motion or rotating mirror. If it has a turntable, turn that function off or remove.)
  • a microwave-safe casserole dish
  • 1 bag of marshmallows (large size)
  • a ruler


  1. Open the marshmallow bag and place the marshmallows in the casserole dish, completely covering the dish with a layer one marshmallow thick.
  2. Next, put the dish of marshmallows in the microwave oven and cook on low heat. Microwaves do not cook evenly and the marshmallows will begin to melt at the hottest spots in the microwave. Heat the marshmallows until they begin to melt in four or five different spots.
  3. Remove the dish from the microwave and observe the melted spots
  4. Take the ruler and measure the distance between the melted spots..

What is going on:

  1. You will find that one distance repeats over and over. This distance will correspond to half the wavelength of the microwave, about 6 cm. Now, turn the oven around and look for a small panel sign that gives you the frequency of the microwave. Most commercial microwaves operate at 2450 MHz.
  2. Now multiply the frequency by the wavelength. The product is the speed of light.

Example: Velocity = Frequency x Wavelength
Velocity = 2450 MHz x 0.122 m
Velocity = 2.99 x (10 to the 8th power) m/s

This experiment activity is found on page 103 of the Explore MyPlate with School Nutrition booklet. For more activity ideas like the one above, check out HKC resource materials. See the Online Store for descriptors and to view the Table of Content and booklet sample pages.