Disclosure: this post contains affiliate links, which means I may receive a commission if you click a link and purchase something at no extra cost to you. Please check out our policies page
for more details.
It’s March, which means the weather is turning from cloudy and cold to spring and sunny.
We decided to do the 1,000 Hours Outside challenge this year, which means we are outside for play, school lessons, and even meals! This is the perfect time of the year to spend time outside too, since it’s not too hot outside (hello, Texas summer) and the sun is shining.
Speaking of the sun shining, this week’s STEM experiment is all about the sun’s rays. We’re learning about how there is more than just the sunshine we see, what it does to our bodies, and how it affects objects.
This experiment demonstrates the effects of sunlight, particularly UV radiation, on materials. When the exposed construction paper fades while the covered area remains unchanged, we can learn about photodegradation and how UV rays can cause chemical changes. It’s a simple way to learn about light and energy!
Time to head outside to learn about the sun’s rays!
How to make the Secrets of UV Rays STEM experiment
Supplies you will need
For this experiment, you’ll need:
- Construction paper – black
- A small object, like a flower, leaf, or bow
- Optional: plastic wrap and rocks
Before you start
You will need access to direct sunlight for several hours to do this experiment. Be sure to keep the experiment away from trees or anything else that can cast a shadow on it.
Instructions
Here is how to do this experiment with your child:
Step 1: Place a piece of construction paper outside with an object on top
Find a flat surface outside that has access to full sun for at least a few hours. Be sure that it won’t be in the shadow of anything, because that will change the experiment.
Place your small object in the middle of the piece of construction paper. You can choose something like a flower, a leaf, stick, rock, or even a hair bow like we chose.
The important part is that there is full sun and the object you choose stays in one spot on the paper.
Step 2: Weigh down the object
If your object does not weigh much, you’ll need to weigh it down before beginning the experiment.
Since our hair bow can easily get picked up by the wind (along with the paper), we decided to place a piece of plastic wrap on top of the paper and bow and weigh it down with some rocks.
If you choose to use plastic wrap, the reflection from it shouldn’t play a significant role in the experiment.
Step 3: Check back
Check back in intervals of time, like every hour, to see how the experiment is coming along. It’s also a great opportunity to see how much the paper changes over time!
We decided to let the bow sit on the paper for a couple of hours and we still saw a significant change to the paper.
Remember: the longer you leave the object and paper out in the sunlight, the bigger the fade on the paper!
The STEM behind the Secrets of UV Rays experiment
This experiment teaches:
- UV radiation
- Photodegradation
- Patience
How it works
The energy from sunlight comes in waves of different lengths, some we can see and others we cannot.
The ultraviolet waves we cannot see have enough energy to break down the chemical dyes in the construction paper, changing its color.
The places where the paper was shaded by the object (the bow, in our case) didn’t receive those rays and so remained the original color.
Ultraviolet radiation
Ultraviolet (UV) light has shorter wavelengths than visible light. Although UV waves are invisible to the human eye, some insects, such as bumblebees, can see them. UV radiation covers the wavelength range of 100-400 nanometers (nm), which is broken down to UVA (315-400nm), UVB (280-315nm), and UVC (100-280nm).
UVC and most of UVB radiation is absorbed by the Earth’s ozone and other atmospheric components, but UVA radiation isn’t as affected by the atmosphere. Because of that, the UV radiation that reaches us is mostly UVA with a little bit of UVB.
These ultraviolet rays can impact our health, like damaging DNA and giving us those nasty sunburns. The intensity of the UV radiation is affected by:
- The sun’s height in the sky – that’s why you are more likely to get a sunburn in the middle of the day.
- Latitude – the sun’s angle is more direct around the equator.
- Cloud cover – remember, the atmosphere can block some (certainly not all!) UVB radiation.
- Ozone – the thicker the ozone, the more protection.
This experiment can lead to discussions about the effects of UV radiation in everyday life, such as:
- Sunburns: UV radiation can damage our skin cells, leading to sunburn.
- Fading of fabrics and plastics: UV radiation causes colors to fade in clothing, furniture, and other materials.
- The importance of sunscreen: Sunscreen protects our skin by blocking UV radiation.
Photodegradation
Photodegradation is the change in a material by light.
Ultraviolet rays are one of the big contributors to fading because they break down the chemical bonds and fade the color in the construction paper. Dyed objects are especially prone to fading, making our black construction paper perfect for showing the effects of UV radiation.
After the object sits on the paper for a few hours, the clear contrast between the faded paper and the unfaded covered area shows the role the ultraviolet radiation played in this experiment. The bow blocked the UV rays, making that covered area stay the original color.
This is a big reason why paintings are typically kept out of sunlight: they will fade over time!
We can connect this experiment to real-world scenarios like:
- Faded clothing
- Cracked plastic
- Sun-damaged plants
Patience
This experiment requires a lot of patience!
The effects of the UV radiation won’t be seen immediately; it will take a few hours to complete this experiment.
This is a great experiment to practice patience and persistence (keep coming back to see if it’s changed!).
More experiments about the sun to try out with your child
- Time Travelers: Engaging Children by Building Their Own Sundial!
- Sunset in a Glass: Exploring the light and color in the atmosphere
- Build a Solar Oven Snack Shack!
Recent Posts
It’s March, which means the winds are picking up and storms can happen at the drop of a hat. And when the winds pick up, what does that mean? We do experiments with it! Enter, the weather...
We've been watching a lot of Star Wars lately, and the kids are now interested in all things Star Wars. The characters, the Force, and even those super cool landspeeders. Even though the...