Testing the "5-Second Rule"

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DIY Experiment Series Asks: Should you follow the 5-second rule?


The "How To" From Science-U

You Will Need

  • Prepared agar plates, available online or at science supply stores
  • Food items for dropping
  • Surfaces to test
  • A hot place to "incubate"


  1. Prepare 2 sets of your "test" foods--we used grapes, carrots, candy, and more!
  2. Make 2 sets of agar plates:
    • -Set 1: Drop a food item on a surface for 1-2 seconds, then rub the item on an agar plate.
    • -Set 2: Drop a food item on a surface for 6-10 seconds, then rub the item on an agar plate.
  3. Incubate! Store the 2 sets of agar plates in a hot area (preferably over 90F) for 2-3 days.

For educators and parents - How to guide young learners in science:

  • Inquiry-based learning (IBL) is a teaching approach that is fundamental for the development of higher order thinking skills (summarizing, analyzing, evaluating, creating). It puts the student in the driver's seat and promotes learning through engaging student-based investigations, following the same process used by scientists.
  • IBL begins by posing a question, problem, or scenario rather than simply presenting facts or a standard method to solve a problem. The learner is actively engaged and investigates concepts to reach authentic meaning.
  • The IBL process can vary, however the basics are as follows:

1. The student creates a testable question of their own.

2. The student obtains supporting evidence to answer the question by making observations, doing research, collecting data through an experiment, changing variables from a previous experiment, etc.

3. The student explains the evidence collected.

4. The student creates a claim (explanation) and justifies it using evidence form the investigation.

5. The student creates predictions for future investigations.

  • Recording information during the IBL process is also important to promote science literacy. The following chart is a helpful tool to guide students through the process.

Guided inquiry map

Questions to ask:

  • Which set(s) of plates grew visible bacteria colonies?
  • Did the set of foods left on a surface for less than 5 seconds grow less bacteria than the set that was left on the surface for more than 5 seconds?
  • Would you follow the 5-second rule? Why or why not?
  • Does it matter what kind of surface (tile/carpet/hardwood) or what kind of food (wet/dry) you're testing?

The science behind it:

  • The type of surface and the amount of time a piece of food is on it can affect how much bacteria will actually get onto the food.
  • Bacteria are least likely to transfer from carpeted surfaces and more likely if moist foods make contact for more than five seconds with wood laminate or tile surfaces. Researchers believe this is because on a smooth surface the area of contact is greater than when food is suspended on the tips of the carpet fibers.
  • Dry foods dropped on carpet have the slowest rate of bacteria migration.


  • Teaching Great Lakes Science (http://www.miseagrant.umich.edu/lessons/teacher-tools/guided-inquiry-process/)
  • Scientific American (http://www.scientificamerican.com/article/fact-or-fiction-the-5-second-rule-for-dropped-food/)
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