If You Drop It Should You Eat It?

Jacob Blauvelt, Reporter

So, here I am: walking out of the diner with a fresh slice of mozzarella pizza, the aroma causing my mouth to water. I can tell how the cheese is going to taste just from the scent. Sadly, I will never know how this masterpiece would have tasted. . . I went to introduce it to my expecting taste buds, then
The slice of pizza had slipped out of my grasp and fallen onto the tile floor! I start to question my options: whether I should just pick it up and go about my business… or accept defeat and throw the slice of soiled pizza away. If I pick it up quickly, it would be safe to eat, right? How fast could the bacteria on the floor really invade my slice of pizza? Some would call this the five-second-rule or the ten-second-rule, and others, the two-second-rule. But, is there any truth to it? Or is it just something we say to allow us to eat off the floor?

During her apprenticeship in Hans Blaschek’s University of Illinois lab, Jillian Clarke considered this question. She found that seventy percent of women use the five-second-rule to eat food off the ground, while fifty percent of men do the same. More importantly, she found that even a very
brief contact with the surface of the floor will contaminate the food, wet or dry. She also discovered that five seconds is far too long, never mind ten. After five seconds, the food will already have acquired anywhere from 150-8000 bacteria. If left for a full minute, the number of microbes found was multiplied by ten. Taking into account that it only takes about ten bacteria of certain strands of salmonella to infect you, you should probably think twice before eating off the ground.

To our eyes, the floor may look clean, but eating off it is still not safe. Floors encounter many different shoe bottoms throughout the day, which have been found to have a ninety-three-percent chance to be contaminated with fecal pathogens. Also, the floor surface makes a great home for bacteria, making the likelihood of the germs spreading to the food even higher.

Is there a short enough time frame, where I could pick the food up within it, there would be no way for what it touched to contaminate it? First, we need to define ‘touch’. We usually think touch means two objects coming into contact with each other. At a subatomic level, atoms resist colliding together because their electrons repel. When touching something or someone you are just feeling the electrons reacting to each other at a subatomically small distance, but nevertheless, a real one.

So, if that is the case, how can bacteria that is on the floor attach to food that has been dropped on it? The positive charge from the protons in an atom or molecule is not always balanced perfectly in space by the negatively charged electrons. Sometimes a molecule is asymmetrical, and this imbalance is permanent, giving the molecule a constant dipole. Meaning, it is like a small magnet. However, even in symmetrical molecules, electrons are constantly moving. At any point in time, they might happen to find themselves on one end of a molecule more so than the other, creating rapidly fluctuating dipoles causing the molecule to act like a magnet. If molecules have a bunch of energy, they will simply glide by one another. Their dipoles and those of their neighbors would not matter much. When cooled down, the dipoles will have more of an effect, because the electrons are moving slower. Therefore, molecules tend to stick together as they cool, going from a gas, to a liquid, then to a solid.

You may be wondering why all this information about molecules is relevant. Well actually, it is extremely important. It is the reason things can get wet. It is also the reason capillary action happens. If you dip a paper towel into a glass of water, you can watch the water climb
up the paper towel, going against the force of gravity. That is because the molecules of water have very strong dipoles, and they are attracted to each other; cohesion and they are attracted to the molecules of the paper; adhesion. This force is stronger than that of gravity, resulting in the apparent climbing of the water. But, how quickly do those forces act? Can two surfaces come into contact briefly enough that their molecules don’t have time to be influenced by intermolecular forces? To understand this, we must delve into intermolecular dynamics; or the computer simulation of the physical movements of atoms or molecules. These simulations need to account for the fastest molecular vibrations of the given material. Typically, time as brief as a quadrillionth of a second is considered. So, the five-second-rule may be true if we renamed it to the one femtosecond rule. If the food dropped spent less time than that on the floor, it is very unlikely that molecules at room temperature would have the time to be influenced by intermolecular forces. Except, maybe we are looking too far, or too small. Objects can become entangled with each other on a macroscopic level. This is seen through the use of velcro. Also, things such as glue, make up, and other adhesives often take advantage of the imperfections – ridges and cracks – in the surfaces they meet. Sticky things can seep inside of these fissures and hold on. Even surfaces that seem smooth to us, when observed closely, are quite the opposite. When two pages slide across each other, they do so easily. But when this friction is multiplied by the number of pages in a large book, such as a textbook or phonebook, and the pages are interweaved, the force is strong enough to lift an entire car.

The adhesion between two objects caused by the shapes of their surfaces contributes to friction and is known as “mechanical adhesion.” This plays a pretty big role in getting floor germs to stick to dropped food. In fact, if two surfaces can mechanically adhere, but aren’t close enough to do so, we wouldn’t say they are touching. And so, by definition, “touching” means that you can mechanically adhere to other object’s surfaces, well, then maybe the five-second-rule shouldn’t be known as the one femtosecond rule, because if they are already touching, it is too late. Instead, maybe we should just accept that eating food off the floor is not advisable.

Come to think of it, maybe we shouldn’t be eating food that is touching anything, because these microorganisms are everywhere, including on you right now. There are more pathogens on your body right now than there are people living in the United States. There are forty-million bacteria in one gram of soil and five-nonillion bacteria on Earth or 5 x 1030. What blows my mind is not how dirty our world is, or how many germs there are; instead, it is the fact that despite those numbers, we don’t get sick more often. Our immune system is amazing, but it relies on the same principles of adhesion that bacteria do. The forces that cause food dropped in the floor to pick up germs are the same forces we need to fight them. They are the same forces that bring us closer together, whether we like it or not.

Works Cited

“Molecular Dynamics.” Wikipedia, Wikimedia Foundation, 23 Oct.

minutephysics. “What Is Touch?” YouTube, YouTube, 21 Nov.
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“Van Der Waals Bonding.” Chemical Bonds,

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“Orders of Magnitude (Numbers).” Wikipedia, Wikimedia Foundation,
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“FACT CHECK: Dropped Food Rule.” Snopes.com,

Franco, Michael. “Does the Five Second Rule Really Work?”
HowStuffWorks Science, HowStuffWorks, 8 Mar. 2018,

“Intramolecular and Intermolecular Forces.” Khan Academy,
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