What am I going to learn?

After a day in the sun, your skin is red, swollen, and sensitive. But you used sunscreen! Granted, it was only Sun Protection Factor (SPF) 5. You wonder if you should have used a higher SPF. Would sunscreen with a higher SPF block more harmful rays from the sun? You decide to conduct an experiment to test out your question and along the way, answer some of the questions above!

What light sources emit UV light?

Can you get sunburned inside?

Does sunscreen actually protect us from UV light?

Where in the electromagnetic spectrum is UV light?

Wh ich sunscreen works the best?

Is there UV l ight i ndoors?

T h e P h y s i c so f

S u n b u r n !

What am I going to learn?

After a day in the sun, your skin is red, swollen, and sensitive. But you used sunscreen! Granted, it was only Sun Protection Factor (SPF) 5. You wonder if you should have used a higher SPF. Would sunscreen with a higher SPF block more harmful rays from the sun? Conduct an experiment to test out your question using black construction paper as a model for your skin!

Some questions to keep in mind during your investigation are: What light sources emit UV light? Can you get sunburned inside? Does sunscreen actually protect us from UV light? Where in the electromagnetic spectrum is UV light?

What light sources emit UV light?

Can you get sunburned inside?

Does sunscreen actually protect us from UV light?

Where in the electromagnetic spectrum is UV light?

Predictions

Answer these questions before doing the lab

1. What do you think will happen to the paper outside in the sun?

2. What do you think will happen to the paper inside?

3. What do you think sunscreen will do for the paper? How will the SPF of sunscreen affect your outcome?

What you’ll need!

sunscreen of various SPFs and one lotion with

no sunscreen

sun or UV light source

scissors

squares of black construction paper

dark pen

What is SPF?The SPF of a sunscreen is a multiplication factor. Your skin already has a natural SPF, and sunscreen strengthens that number. If you can stay out in the sun for 15 minutes before your skin burns, using a sunscreen with an SPF of 10 would allow you to stay out in the sun for 10 times longer (100 minutes), assuming the sun doesn’t get stronger that day!

Let’s Experiment!

Steps:

1. Set aside one paper square and apply lotion with no sunscreen.

2. Coat the other squares of black construction paper with sunscreen. Rub into paper until sunscreen absorbs

2. Label each square with the SPF you applied.

3. Place the paper squares outside in direct sunlight. Weight them down with coins.

4. Repeat steps 1-5 with a second set of papers and place them indoors under a regular light.

8. At the end of the day, compare your squares to the fade-o-meter below to determine how much they faded. Record your observations in the chart on the next page and graph them on the following page.

Why do I need to apply lotion with no sunscreen to one square?

Lotion without any sunscreen will act as our “experimental control,” or point of reference. This means we will check whether the sunscreen protected our paper against the paper with lotion (no SPF).

Why do you think we are testing paper inside as well as outside?

5. Leave the papers outside in the sun for at least 5 hours. To increase the effect, collect the papers at the end of the day and replace them in the sun the next day.

6. Last, repeat your experiment by covering the coated paper with glass instead of coins or test various other oily substances (olive oil, vasoline, etc.) on the paper.

Results

SPF of lotion, or type of material Number on Fade-O-Meter

Lotion(no SPF)

Notes:

1 2 3 4 5 6

Fade-O-Meter

7 8 9

Graph Your Data!

SPF

Fad

e-O

-Me

ter n

um

be

r

1

2

3

4

5

6

7

8

9

What happened?

Answer these questions after you do the lab

1. What did you observe happen to the paper outside and inside? How did this compare to your predictions?

2. Is there a relationship between SPF and the amount the paper fades?

3. What are some sources of error that might have affected your experiment?

4. How well do you think the construction paper models your skin? How might it be different from how sun affects your skin?

5. If you tested out other substances and materials, like glass, how could you use the fading factor of your sunscreened squares to figure out the SPF of these other materials?

Why did I see what I saw?

The electromagnetic (EM) spectrum, shown below, describes different types of light. Light is referred to as an EM wave because it is made up of both electric and magnetic waves moving together through space. The EM spectrum is arranged by wavelength with longer wavelengths to the left, shorter wavelengths to the right. We are most familiar with visible light and all EM waves in the spectrum are types of light. Did you know x-rays were a type of light?

Our eyes can only see the small portion of the EM spectrum called “visible light” which includes all the colors of the rainbow. Everything else in the spectrum is invisible to our eyes. For example, ultraviolet (UV) light is a part of the spectrum we humans cannot see, but other animals can see UV light, including bees, butterflies, and reindeer.. UV light has a smaller wavelength than visible light, which is why it is to the right of visible light. Other types of light we cannot see include radio waves, X-rays and microwaves.

Though we cannot see UV light, we can detect it in other ways. One way is sunburn! When your skin turns red from sitting in the sun, it is detecting the presence of UV rays. It also hurts! What are some ways we detect radio waves? How about X-rays?