My hypothesis is that the petri dish with the swab from the apple slice that was on the floor for the longest time (10 seconds) will have the most bacteria on it. This is because it had the longest time of contact with the dirty surface, allowing more bacteria to attach to the apple slice.

See if the 5-second rule is real because friends believe it to be true.

Watch experiments online and see how others (Mark Rober, Science News) conduct this experiment.

Research on which fruits or vegetables provide the best way to make this experiment work and found apples are easy and good to test with.

Make a list of all the materials required.

What is the best time to conduct this experiment. Selected 0 for control, 5 and 10 seconds for test.

Controlled Variables:

• Location of apple slices contacting surface
• Evenly contaminated surface
• Storage of the petri dishes
• Food used

Dependant:

• Amount of time the apple slices touch the surface

Independent:

• Amount of growth of the bacteria

1. Make liquid agar by boiling water and dry agar solution.
2. Place the agar solution into the petri dishes and let it cool for 1-2 hours. Cover the petri dishes so it does not contaminate the liquid agar solution.
3. Wear gloves before taking any swabs.
4. Take a swab of one clean apple slice and rub the swab onto a clean petri dish.
5. Close the petri dish and place label with “0 SECONDS”, tape the petri dish closed and set it inside the container.
6. Take a second clean apple slice and place it on the dirty surface for 5 seconds. Time accordingly.
7. Using tongs lift the dirty apple slice immediately after 5 seconds, swab the dirty apple surface with a clean swab and rub the swab onto another clean petri dish.
8. Close the petri dish and place label with “5 SECONDS”, tape the petri dish closed and set it inside the container.
9. Take the third clean apple slice and place it on the dirty surface for 10 seconds. Time accordingly.
10. Using tongs lift the dirty apple slice immediately after 10 seconds, swab the dirty apple surface with a clean swab and rub the swab onto the third clean petri dish.
11. Close the petri dish and place label with “10 SECONDS”, tape the petri dish closed and set it inside the container.
12. Discard the swabs and the apple slices in the appropriate waste / compost bin.
13. Take a picture of the three petri dishes, close the container and place it in a dark and warm environment for 5 to 8 days.
14. Continue to monitor and take pictures once a day (morning or evening) 24 hours apart to see the bacteria growth on the petri dishes.
15. Record the results.
16. After the experiment is completed, ensure the agar solution and bacteria in the petri dishes are discarded properly in the compost bin.
17. Discard petri dishes in the waste bin.

Day #1 – No growth observed on any of the petri dishes

Day #2 – No change observed on any of the petri dishes

Day #3 – No change observed on any of the petri dishes

Day #4 – No change observed on any of the petri dishes

Day #5 – No change observed on any of the petri dishes

Day #6 – Little growth observed on the petri dish with 10 seconds but no change in 5 and 0 seconds. Second experiment is not showing any growth on any of the petri dishes.

Day #7 – Little growth observed on the petri dish with 10 seconds and small growth in 5 second and no change to 0 seconds. Second experiment is showing growth on 0 second but not on 5 second or 10 second petri dishes.

Day #8 – Further growth in 10 second dish and in the 5 second dish. The 5 second dish also has a second growth being observed which is small. 0 second dish has no growth still. Second experiment is showing same results as Day 7. No additional changes to the second experiment.

DATA

First Experiment

Second Experiment

Based on the pictures, it is clear to see that the apple slice that was on the floor for the longest time of 10 seconds collected more bacteria than the slice that was on floor for 5 seconds. The apple slice that never touched the floor had no bacterial growth.

The results from the second experiment show that ensuring there are no contaminants and location of where the apple slice was “dropped” is important.

This experiment shows that the 5-second rule for eating food after it has dropped on the ground is not always true. Eating food that has dropped on the ground can be harmful to our health as it collects bacteria. The second experiment shows that sometimes, there is already bacteria on surfaces which can grow even if it has not fallen on the ground, but this is in much smaller amounts which our body can fight off.

Making sure that the surfaces of the petri dish with the agar solution, the swabs and the food surface for the control time of 0 seconds should be clean. Otherwise, as experiment 2 shows, you can get data that doesn’t meet the hypothesis. Contamination in experiments like this is possible and that’s why you should conduct multiple experiments to make sure you can get data that is valid.

Some of the challenges in this experiment were making the agar solution because it’s hard to make sure that when you make the solution that you don’t have contamination. You can also buy the solution but keeping it in the right conditions is important as contaminants can be present in that too. This is why I conducted two experiments. Next time, I would conduct more experiments with different slices, different surfaces and using clean swabs that are not Q-tips. Q-tips can sometimes leave behind fibres which can contaminate the surface as well.

This experiment did confirm the hypothesis with the first set of petri dishes and the expected outcome was observed. It is always a good idea to clean the food when it falls on the ground before eating it or putting it into the compost bin and discarding it. Never eat food fallen on the ground even if it is immediately picked up as bacteria will most likely attach itself to the food.

There was a second experiment with different slices with second set of petri dishes. With the second experiment, none of the 5 second or 10 second petri dishes had any growth. But one petri dish of an apple slice swab that never touched the ground (0 second) was observed having a very small amount of bacterial growth. This could have been because of contamination and / or the storage location being different from the first experiment.

Rober, Mark. "Is the "5 Second Rule" Legit?" Science Channel, Science Channel, 2 Feb. 2016, https://www.youtube.com/watch?v=Q4MYg9gHXPs. Accessed 06 Oct. 2024.

Sanders, Laura. "It’s time to retire the five-second rule." Science News, 23 Sept. 2016, https://www.sciencenews.org/article/its-time-retire-five-second-rule. Accessed 06 Oct. 2024

"THE 5-SECOND RULE and FOOD SAFETY." ABC Oriental Rug & Carpet Cleaning Co., https://www.abc-oriental-rug.com/5-second-rule.html. Accessed 03 Mar. 2025

“Dropped your food? It's okay to pick it up and eat it in 5 seconds.” FOOD SAFETY LATEST, 18 Mar. 2017, https://foodsafetylatest.blogspot.com/2017/03/dropped-your-food-its-okay-to-pick-it.html.

- My dad for helping me with everything I need 

- My brother for telling me everything that I will need to know to be successful for the science fair

- Mr.Downey for hosting our school`s science fair

- My family for encouraging me