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A Beautiful Sunny Day

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Updated on Feb 04, 2012

Grade Level: 6; Type:Environmental

The purpose of this project is to test sunscreens from the lowest number to the highest.People depend on sunscreen to protect their skin from the sun’s ultraviolet radiation.People believe that a higher number equates to greater protection.

  • Does sunscreen block the sun’s ultraviolet radiation?
  • Does a higher SPF number protect skin more than a lower number?

Ozone in the earth’s atmosphere filters out much of the sun’s harmful ultraviolet radiation.Chemicals produced by humans have been harming that protective layer.In the 1970s, scientists noted a thinning of the ozone over Antarctica that grows each spring, increasing the danger of ultraviolet radiation as it shines on earth’s surface and humans.

In this experiment, the independent variable is the sunscreen SPF applied to the plastic.The dependent variable is the exposure of the sun-sensitive paper.The constants include the photo paper, the plastic bags and the conditions.

  • Sunscreens with a range of SPF numbers.For example, 15, 30 and 45 or 15 and 70.
  • Plastic bags—as many as the number of sunscreens plus one for the control.
  • Sun-sensitive paper.(This can usually be found at kids’ stores that stock lots of crafts.)

  1. Close the blinds or shades in a room to block the natural light.
  2. Label the plastic bags with the SPF number for the sunscreen being tested.
  3. Place one square of sun-sensitive paper inside each of the plastic bags.
  4. Place three drops of one sunscreen on the outside of the bag labeled with its number.Spread the sunscreen as evenly as possible.
  5. Repeat the step above with the other sunscreens.
  6. Leave one bag untreated as the control.
  7. Place the bags outside in direct sun, making sure that they receive equal light.
  8. Bring them back inside after 3 minutes or one of the squares—usually the control—turns completely white.
  9. Observe the sun-sensitive squares and make conclusions about the effectiveness of each sunscreen.

The results of the experiment might be visually represented by a modified graph:

Terms/Concepts: Global warming; Ozone; Ultraviolet radiation

Reference:

Jane Frances Healey taught for many years at both the college and high school levels. Currently, she's a freelance writer in the San Francisco area, and she enjoys doing research on a wide variety of topics.

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