This would be a fun experiment for any group of kids over 3 years old. It is an activity for the Girl Scout badge Let’s Get Cooking, combined with an activity I adapted from the Junior Girl Scout Handbook. My troop did it two years ago at the beginning of our work on the badge. It helped the girls understand why it’s so important to wash our hands before preparing food, and even the leaders were surprised at the results of different hand-cleaning methods.
There are two phases to be done on the first day, then follow-up a week later. My troop was so interested in the results that we had two more weekly follow-ups to see how things progressed. (Phase Two could be done by itself, if you aren’t able to follow up.)
You will need:
- a sink with hot and cold water
- 3 clean cloth towels, or paper towels
- waterless hand sanitizer
- enough apples to make 1 big chunk per kid
- cutting board
- sharp knife
- 5 clean containers with tight-fitting lids, each big enough to hold 1/5 of the apple chunks–I used old yogurt tubs
- masking tape and marker to label containers
- some kids with normally dirty hands. I told the girls, “If anybody needs to use the bathroom, go now but don’t wash your hands.”
Wash the apples and your own hands thoroughly with hot water and soap, and cut up the apples immediately before beginning the experiment.
Divide the kids into 5 groups:
- Group 1 washes their hands really fast with cold water and soap–you know, like most people in a hurry would do–and dries them on Towel 1 or with paper towels.
- Group 2 rubs their hands together under hot water for a while, with no soap, and dries them on Towel 2 or with paper towels.
- Group 3 washes their hands thoroughly with hot water and soap and dries them on Towel 3 or with paper towels.
- Group 4 uses hand sanitizer.
- Group 5 does not clean their hands in any way.
As each group finishes cleaning their hands (or not), give each kid a chunk of apple. Have them rub the apple with their hands until they feel sure they have touched every part of its surface. Put the apples in a container, seal it, and label it with the hand-cleaning method. Put away the containers until follow-up, making sure to store all of them in the same temperature and lighting conditions. My troop had a large plastic storage bin to keep our supplies at the church where we met, so we put our apple tubs in there.
You will need:
- a sink with hot and cold water
- cloth or paper towels
- waterless hand sanitizer
- vegetable oil
- some type of highly visible specks–I used some very old chili powder that had lost its zing. Don’t use new chili powder or other peppery things that might burn sensitive skin!
- some kids–the starting condition of their hands is not important, so this can be done immediately after Phase One.
Divide the kids into 4 groups. (In my troop, I just explained what we were going to do and then asked for 4 volunteers–not all the girls wanted to do this part, but they all wanted to watch!) Explain that this is going to be messy and they should not touch anything–especially their eyes; they don’t want specks in their eyes–until their hands are fully clean afterward.
Pour about 1/2 teaspoon of oil into each kid’s cupped hands and have them rub the oil all over their hands.
Have Group 1 hold their hands over the sink. Sprinkle hands with specks. Explain that these represent dirt and germs. We are going to see how well different hand-cleaning methods remove dirt and germs from our hands. Have Group 1 wash their hands really fast with cold water and soap (like Group 1 in Phase One), then hold them up for everyone to see. How many specks came off? Then let them use hot water, soap, and towels to remove the rest of the specks and oil.
Do the same with Groups 2, 3, and 4, with each of them using the same hand-cleaning method as their group in Phase One.
Discuss what you’ve learned.
One week later, get out the containers and remind everybody what you did in Phase One. Carefully open each container and look at the apples. How have they changed? What is different about the apples from the different groups? Discuss what you’ve learned.
Our Results (Spoiler Alert!!!)
When we did Phase Two,
- Girl 1 was horrified by the way the specks and grease stayed on her hands at first. She had to use a lot of soap!
- Girl 2, with hot water but no soap, had less trouble; we speculated that this had less to do with hot water’s ability to remove “germs” than with its ability to cut the grease that was making the specks cling to her hands.
- Girl 3 got clean quickly and easily.
- Girl 4 found that hand sanitizer turned the oil into a sticky mess, with specks intact, that she could move around on her hands but couldn’t remove; it became more gummy as the alcohol evaporated. She tried to rub it off with a paper towel, which stuck to her. Yuck!!! She finally resorted to hot water and soap.
Conclusions: Both hot water and soap are important for effective cleaning. Hand sanitizer may kill germs, but it doesn’t take stuff off your hands. But after that second conclusion was stated, several girls told of experiences with rubbing hand sanitizer on things like ink and seeing it vanish. Someone theorized that if the stuff will dissolve in alcohol, it will evaporate off your hands when the alcohol does. (I’m not sure if that’s correct, but it sounds plausible.) Additional conclusion: Chili powder is not soluble in alcohol.
Our week-old apples had turned brown and were growing mold. Group 4 (hand sanitizer) had as much mold as Group 5 (unwashed). Groups 1 and 2 had less. Group 3 (hot water and soap) had the least. The girls agreed that the apples were not as gross as they’d expected and began chanting, “One more week! One more week!” with great enthusiasm.
After two weeks, the apples were much mushier and moldier, with the less-moldiness of Group 3 more obvious than before. Oddly, Group 1 (cold water and soap) was less brown and mushy than all the others. Nobody could explain it. We could now see that Group 1 had mostly white mold and Group 2 had mostly black mold. We theorized that heat kills some molds better than others, and soap removes other molds better than the heat-sensitive ones. “ONE! MORE! WEEK!!! ONE! MORE! WEEK!!!” “Okay, okay, stop yelling.”
After three weeks, we could smell rotting apples before we even opened our storage bin. All the apples were totally disgusting except Group 1, which seemed disturbingly well-preserved except for the moldy spots. There were tentative suggestions that perhaps the girls in Group 1 just happened to have cleaner hands before starting the experiment. The black mold had produced fruiting bodies, which fascinated some of the girls. Group 4 (hand sanitizer) was now the most moldy, but Group 5 (unwashed) had the greatest variety of mold, four different kinds that we could see, and was visibly the most rotten.
- Yeah, yeah, we all know that hot water and soap are best for getting hands really clean. Seeing the differences motivated us to be more careful about proper handwashing.
- Hand sanitizer does not kill mold, at least not all species of it. All of us were surprised by that, but after all hand sanitizer is marketed to kill bacteria, not mold.
- Cut-up apples at room temperature go bad, no matter how clean they are.
- One girl has decided she wants to be a “mold-ologist” when she grows up.