Science Buddies: "Ask an Expert"

Hi Kristi and Michaela,

This sounds like a great project to pursue. However, I am unsure whether photographs would be able to capture the relative changes in microbes produced by the different methods of hand-washing. An alternative way of collecting data would be to use agar plates.

You can read more about how agar plates may be used on this page: https://www.sciencebuddies.org/mentorin ... ?from=Home
Though the above link is addressing a different experiment, the agar plate and colony-counting methods for assessing bacterial content can be used for your project, too!

You are correct about the *dependent variable* being the amount of germs left on the hands after washing.

Your proposed experiment has multiple *independent variables*: (1) duration of hand-washing; (2) water temperature; (3) use of soap.

Since you have three independent variables, your experiment will require eight trials:
15 sec, cold, with soap
30 sec, cold, with soap
15 sec, cold, without soap
30 sec, cold, without soap
15 sec, warm, with soap
30 sec, warm, with soap
15 sec, warm, without soap
30 sec, warm, without soap

This will require careful use of controls. You will want to make sure you keep the following the same (controlled) for all eight trials: (1) person who is doing the hand-washing; (2) method of "dirtying up" the hands before washing; (3) method of hand-washing (washing between the fingers, the backs of the hands, or just the palms, etc.); (4) new, clean towel for drying hands.

Hope this helps! Let us know if you have further questions.

Grace Lin

Thank you so much for your detailed response! VERY helpful.

We will look into the agar plates as a way to assess the bacterial count. For "germs" we are using a product called "glo germ", that, if properly used, shows up using a "black light", thus producing an image of the amount of germs left on the hands. Perhaps we will just use the pics as a visual aid?

Thanks again for all your help!

We will keep you posted as to how this goes!!


Have a great 3 day weekend:)

Kristi & Michaela

For a science fair project, you might be able to get away with just showing pictures especially if the results are dramatically different from one trial to another. A proper scientific paper would require you to express your results as numbers and to do statistical calculations to back up your conclusions. Doing bacterial experiments with agar plates is traditional way health officials use to do bateria counts. In your case, you could quantify your bateria as a percentage instead of a bateria count.

I think your "glo germs" are a much more fun way to see the effects of hand washing. Since it's visual, you'll be able to better communicate your results to the judges and to yourself. You will have a better time with the experiment from seeing and showing your bacteria instead of showing just the numbers.

One note of caution. Before you get your hands soaked into bacteria, make sure you have a camera or setup that can take pictures in the dark. I've seen some exibits that didn't come out as planned because their camera/film wasn't sensitive enough or their camera setup wasn't stable enough to capture low level flourescence. Good luck.