At-Home STEM Activities: Ice Cube Race
Learn how different colors interact with heat in this simple solar-powered activity!
This activity is geared toward elementary-level learners, but can easily scale up or down depending on existing science knowledge. Younger children may appreciate performing the experiment with less emphasis on the background and concluding information, while older students may choose to supplement this lesson with in-depth research on wavelengths and energy.
Background
The Sun releases lots of energy. Some of that energy reaches Earth in the form of light. This is why you wear sunglasses on a sunny day!
Light from the Sun travels in waves—like water in the ocean. Light waves come in different sizes, which are called wavelengths.
Light with the largest wavelengths—the biggest distance from the top of one wave to the top of the next wave—looks red to our eyes. Light with the shortest wavelengths—a small distance from the top of one wave to the top of the next one—looks violet. This illustration shows how different wavelengths cause different colors of light. White light is made of all of the wavelengths combined.
Look around you: you might see green leaves outside, blue shoes on the doormat, a yellow bowl full of red apples, or an orange cat napping in the windowsill. The world is full of objects in many beautiful colors! The color of objects also comes from wavelengths.
When white light (which contains all the wavelengths) hits the surface of an object, the object reflects some light waves and absorbs others. The color that we see is the wavelength that is being reflected. For example, blue shoes look blue because they are reflecting blue light; the shoes have absorbed all the other wavelengths. A yellow bowl reflects yellow light and absorbs all the others. A black object absorbs all wavelengths of light and reflects none.
Now let’s perform an experiment to see how different colors react to heat.
Materials
Construction paper or cardstock in several different colors, including black and white
Scissors
Ice cubes
Waterproof tray (cookie sheet is a good option)
Direct sunlight
Process
Cut one square out of each color of paper
Review: which color of light is each square reflecting?
Place the paper squares onto your tray—it may be a good idea to tape or weigh down the paper if you’re taking the tray outside to get sunlight
Put one ice cube onto each square
Make a prediction: do you think the ice will all melt at the same time, or will some cubes melt faster? Which ice cube do you think will melt first? Why?
Take your tray outside, or balance on a sunny sill or countertop
Check back periodically until the ice cubes have melted (we checked ours every ten minutes for just over an hour); if desired, make notes of the order in which the cubes melt
Who is the winner of your ice cube race? Do the results of your experiment match your prediction? Did anything surprise you about your results?
Conclusion: what happened?
We know that:
Heat and light are two kinds of energy
Different colors of light have different wavelengths
Objects get their color by reflecting one of the wavelengths in white light and absorbing the rest
But what does this have to do with your ice cubes melting?
Since light is energy, an object that absorbs lots of light is taking in lots of energy. Some of that energy gets changed from light into heat.
Remember that black objects absorb all the wavelengths of light—so a black object (like a piece of paper) in the sunlight is absorbing a lot of energy and producing lots of heat. A white paper reflects all the wavelengths and absorbs none—so it does not have enough energy stored to create very much heat. Left in the sunlight, your black piece of paper absorbed more energy, and became warmer, than all the other pieces. The ice cube on the black piece of paper should have melted first, and the cube on the white paper should have melted last.
How did the rest of your paper squares come out in the race? What does that tell you about the wavelengths of light that they are absorbing?
Take it further: knowing what you now do about colors and heat absorption, how could you plan your wardrobe to correspond with the weather? What color shirt would you want to wear to stay cool outside on a very hot day?
Practical note: At first we used a piece of plain white printer paper to set up the white square on our experimental grid. We were surprised to see, at the 10-minute check-in, that the ice cube on the white paper was melting more quickly than the ice on some of the colors. We realized that the melted ice had soaked through and caused the white paper to become translucent, so that ice was actually on a BLUE surface (the tray underneath was showing through)! We immediately found some white cardstock and placed the ice cube onto TWO squares—which was thick enough to keep the melted ice from soaking through. After this swap, the ice behaved in the way we’d expected.
