Tag Archives: Density

Why You Gotta Be So Dense

Cooking 101: What happens when you put oil into a pot of water? Well, as any pasta lover should know, the oil floats to the surface creating its own layer that rests right above the still water beneath. But why is that?

The answer to this question, my friends, is density.

density.Density, in the simplest of terms, is how much of something an object has. More technically, it represents how much mass an object contains, with respect to its overall volume. Most of us are familiar with the mathematical formula for density, D=M/V, which helps to visually show us this relationship. Typically, larger, heavier objects hold more mass, where as smaller, lighter ones hold less. Comparing that to the size, or volume, of the object will determine its overall density. This will also help to judge how they may react in different mediums, such as water.

density2If we cycle back to our original question as to why oil floats above water, we can see that the oil must be lighter than the water for it to rest on the surface. In fact, oil is lighter, or less dense, than our medium, which is more dense, thus explaining the phenomenon that we observe when cooking.

Within the marine world, this concept applies to all objects that come in contact with the water. If it contains more mass than its overall volume, the object will sink and vice versa. If you drop a strawberry into the water, which actually weighs less in comparison to the amount of space it takes up for itself, it will float! As for a piece of clay, its mass is heavier, meaning that it will sink. On a more complex scale, these objects might react differently within the oceans that surround us. Because marine waters contain a higher salinity than freshwater, our strawberry and piece of clay will decrease in density, as salt water is more dense. As a result, our strawberry will continue to float to the top while our piece of clay may surface as well instead of sink.

Written by: John Cornett

Salinity and Water Density

When swimming in salt water you can make observations on more than just the salty taste. An observation you may have made is that you are more buoyant, or you float more, in salt water than in fresh water. This is a result of the oceans salinity, the amount of salt in the water. Density is the amount of matter in a given space or area. When a volume of water is replaced by an item of greater density than the water, the object will sink. Likewise, if a volume of water is replaced with an object that is less dense than the water, it will float towards the surface.

This physical happening can be observed when pouring fresh water into a pitcher of salt water. The fresh water, when poured slowly, will remain on the top of the salt water. A small layer forms where the two bodies of water meet, called a Halocline. You can also observe the difference in density by using an egg. Place an egg in fresh water and watch as it sinks to the bottom. When placed in salt water it will float. The egg was denser than the space it replaced in the fresh water causing it to sink and was less dense than the salt water causing it to float. When placing the egg into the pitcher that had the fresh and salt water the egg floated right at the Halocline.

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