Big Myths of Everyday Science

The myth: Food that you drop on the floor is OK to eat if you pick it up within five seconds (a.k.a. the "Five Second Rule"). The reality: Germs are on the floor, and if food lands on the germs, they will stick to the food immediately. This is especially true in the kitchen, where bacteria such as salmonella thrive. Seen here is a salmonella culture, so ask yourself: Do you want to eat that?

The myth: Acids will burn your skin, and even disfigure you. The reality: Hundreds of different acids exist, and most of them aren't strong enough to damage your skin. Vinegar and citric acid are two weak acids that we consume frequently. However, some acids are corrosive. Hydrochloric, nitric and sulfuric acids can damage skin -- like that of the woman in this picture, who was burned by sulfuric acid from batteries -- but not all acids will do so.

The myth: Brain cells don't regenerate. The reality: The reason people believe this myth is that scientists thought for a long time that complex brains would be disrupted by new cell growth. In 1998, however, scientists in Sweden and at the Salk Institute in La Jolla, Calif., discovered that brain cells can regenerate. The learning and memory center of the brain can create new cells. Even better news is that Steve Stice, a University of Georgia stem cell researcher, discovered a process to create replicas of human embryonic stem cells that can morph into brain cells.

The myth: A penny dropped from a tall building can kill someone on the ground. The reality: While people may think a penny dropped from the Empire State Building would pick up enough speed to kill a person on the ground, this just isn't true. The non-aerodynamic nature of a penny, as well as its relatively small mass, keeps this from happening. A person on the ground would most certainly feel a sting from the impact, but the penny wouldn't kill.

The myth: Lightning doesn't strike the same place twice. The reality: Lightning can absolutely strike the same place twice. In fact, it's actually quite common -- the Empire State Building is struck by lightning about 25 times per year, for example. Lightning favors tall buildings and trees, but in a large field, lightning is likely to strike the tallest object several times before it moves sufficiently far away to find another tall target. Above, multiple bolts of lightning strike the ground in the desert north of Scottsdale, Ariz., during a late evening storm.

The myth: There's no gravity in space. The reality: Yes, there is a lot of gravity in space. So much, in fact, that gravity is what causes stars to orbit the center of a galaxy, Earth to orbit the sun and a satellite to orbit the Earth. The reason that astronauts seem to be weightless in space is that they are orbiting Earth; they're falling towards it, but moving sufficiently sideways to miss it. In short, they're falling but never landing. At orbit height, about 250 miles (402 kilometers) above Earth, gravity is only reduced by 10 percent.

The myth: There is a dark side of the moon. The reality: The dark side of the moon only exists as a Pink Floyd album. The sun illuminates every part of the moon at some point. There is, however, a side of the moon that is never visible from Earth. This is caused by tidal locking, which causes the moon to take just as long to rotate around its own axis as it does to revolve around Earth. We always see the same side of the moon, but the other side isn't always dark -- when we have a crescent moon, sunlight mostly illuminates the side we don't see.