Each fall, the leaves of the trees begin to turn colors, creating a beautiful backdrop that only nature can provide. As the leaves begin to fall and temperatures begin to drop, you start seeing typical fall decorations appear in preparation for Halloween and Thanksgiving.
Along with scarecrows, gourds, cornucopias, and black cats, you're also likely to see a lot of large orange objects. What are we talking about? Pumpkins, of course! All you have to do is look around to find jack-o'-lanterns decorating the front porches of houses everywhere.
One popular party game that often makes an appearance in the fall is bobbing for apples. It can be so much fun to tie your hands behind your back and attempt to retrieve a floating apple from a large tub of water.
If you've ever dipped a pumpkin in the bathtub or thrown one into a lake, you know for a fact what might surprise many people: pumpkins do indeed float! But how is that possible? How can they not be too heavy to float?
To learn why we — and pumpkins! — float, we only need to turn to science. Particularly, we just need to consult an ancient Greek scientist named Archimedes. Hundreds of years ago, while taking a bath, he discovered the secret to floating and jumped naked from the tub to run the streets, shouting “Eureka!" and explaining what he learned to anyone who would listen.
Basically, Archimedes' Principle (as it came to be known) holds that an object immersed in a fluid will be buoyed up by a force equal to the weight of the fluid it displaces. Simple enough, right? Don't worry! You're not the only one who needs that clarified a bit more.
Think of it this way: if you place a pumpkin into a bathtub full of water, some of the water has to get out of the way to make room for the pumpkin. The water that gets out of the way is displaced from where it used to be.
Where does the displaced water go? There's only one place for it to go: upward. That's why the water level rises when you put the pumpkin into the bathtub. But gravity is still pulling that displaced water back down, and it wants to return to where it came from.
The only problem is that there's now a pumpkin where the water used to be. Fortunately, water has a density of about 62.4 pounds per cubic foot. That means it can push back on the pumpkin with about 60 pounds of buoyant force.
Since the pumpkin is less dense than the water, the water is able to push the pumpkin up quite a bit, so that it floats. If the pumpkin were denser than water, the water would not be able to generate enough upward force. In that case, the pumpkin would sink.
Based upon this principle, we can conclude that any object less dense than water will float. On the other hand, objects denser than water will sink. Pumpkins, although large, aren't very dense because they are mainly hollow inside. Given their large size, though, they displace a large amount of water. With a mainly hollow interior, it's easy for a pumpkin to weigh less than the large amount of water it displaces!