Wishy Washy

We will be testing what type of agitation works best when washing hands.
Klaire Xiao Maia Mihai
Grade 5


If you use a lot of agitation, then most of the germs will go away, because of the friction caused by rubbing your hands together when you wash them with soap and water.


How Do Petri Dishes Work? The agar and other ingredients are dissolved in warm water and poured into the dish and left to cool down. Once the medium solidifies, a sample of the organism is inoculated ("plated"). The dishes are then left undisturbed for hours or days while the organism grows, possibly in an incubator.

What Are Petri Dishes? A Petri dish is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured, like fungi and small mosses. The container is named after its inventor, German bacteriologist Julius Richard Petri. It is the most common type of culture plate.

Why Are Petri Dishes Used? Petri dishes are used in biology a lot to cultivate microorganisms such as bacteria, yeasts, and molds. It is most suited for organisms that thrive on a solid or semisolid surface.

How Can Different Types Of Agitations, Affect How Many Germs Are Left On Your Hands?

 Assume that your hands are dirty, and you only rub back and forth on your palms. That means that the inbetweens of your fingers and the back of your hands are not washed with soap, which leaves 70% of the germs still on your hands. If you wash your hands with proper agitation back and forth, on your palms and the back of your hands, then rub in between your fingers, and do a circular motion, most of the germs should be gone.


Manipulated: The type of agitation.

Controlled: How long you washed your hands for, what we touched to get our hands dirty, how long we touched those thing for, and how long we left them to sit.

Responding: the amount of growth in the petri dishes



1. Gather materials (petri dishes, gloves, nutrient agar, water, sterilized cotton swabs)

2. Prepare petri dishes:

Heat water and agar to 50℃. Then distribute solution in petri dishes

3. Get your hands dirty

4. Wash them with soap and use one of the three types of agitation

5. Rub q-tip on your fingers, then on the petri dish

6.Repeat 3 times, exactly the same

7. Repeat with the other types of agitation making three petri dishes for each type of agitation 

8. Observe and record the changes over 6 days


 On day one, nothing changed.  However, on day 2, test 3a and the control  had some bacteria growth. On day 3, test 1b and 3a was showing  bacteria growth. in the rest of the days all of the petri dishes seem to be growing.


The purpose of this experiment was to help people understand which type of agitation is effective when washing hands. In our results we found that one of our test's performece was worse than our conrtol wich leads us to belive their was some conamanation in our project. Also, the last time we did this project we had diffrent results and test 1 peformed the best.


The method that performed the worst was #2 (in between finger motion), followed by hand washing method #3 (rub palm with opposite hand). the best method was #1 (rubbing hands together). We think the best method was 1 because it covered the most area on the hands out of all of them. Our hypothesis was correct, the more agitation, the better.


 For more accurate results, next time we should do the experiment together, because last time Klaire did it by herself, the petri dishes solidified too fast. So, if we would have worked together, then the work would have been finished fast enough, before the petri dishes solidified. An extension we would do is to add more types of agitations. This is important because especially in covid you have to make sure that you are washing your hands properly. Next time we will be better prepared, and the experiment will go smoother.

Sources Of Error

  • The petri dishes weren't all filled the same 
  • Some of the petri dishes were already more solidified which could have made the bacteria grow slower 
  • The cotton swab could have touched something else before coming in contact with the petri dish


Mrs. delorme and our parents