Would one drown in a deep pool of baby oil?
February 7, 2015 1:19 PM   Subscribe

If you dove into an 11ft pool of baby oil, would you be able to push yourself to the surface or would you drown? AKA what allows us to float?

A friend and I were discussing the idea of floating in water. How water allows you to float. I'm going to sound like a fool here because I know nothing about the properties of water that allow you to float. But he brought up the idea that another liquid, like baby oil or olive oil would not allow you to float for being too "slippery". This is all theoretical but it seemed like an strange idea to me but totally possible. That if you dove into an 11ft pool of baby oil, you would not be able to push yourself up to the surface.

I realize this question has no practical purpose. :)
posted by tunewell to Science & Nature (14 answers total) 3 users marked this as a favorite
 
It's just density. If you're in a liquid that's more dense you than, you float. If you're in a liquid that's less dense than you, you sink.

Complication: your density is to an extent up to you. Take a big breath and your mass stays the same but volume increases, so you become less dense. Exhale fully and you mass the same but occupy less space, and become more dense.

You're much denser than baby oil and would sink in it.
posted by ROU_Xenophobe at 1:30 PM on February 7, 2015 [8 favorites]


Flotation, or buoyancy, is a matter of density, not slipperiness. The old saying that oil and water don't mix is because oil is less dense than water. The density of baby oil is 830 kg/m3 while the density of humans is about 985 kg/m3. Since humans are more dense than baby oil we sink. The reason we float in water is that the density of freshwater is 1000 kg/m3. Salt water is even denser so it is easier for us to float in the ocean or the Great Salt Lake.
posted by plastic_animals at 1:34 PM on February 7, 2015 [8 favorites]


It's a density thing -- the human body is less dense than seawater so we are naturally buoyant in seawater (taking into account the air in our lungs!). All people have slightly different body densities, and it varies constantly by a small amount -- one key reason being the air in our lungs is very low density, so when we breathe out, our density is higher (less air), and when we breathe in, our density is lower (more air).

The question you ask has 2 different answers. Looking up the density baby oil, it is lower than that of a human body, so a person would sink. HOWEVER, "would you be able to push yourself to the surface" is a different question entirely and is a question of physics. When you swim, you are exerting a force. Think of someone swimming through a pool -- they are able to move laterally because of the force they are creating by the movement of arms and legs through the fluid. So the question really becomes, is a person able to swim vertically through a column of baby oil, or is the downward force too much for the person to combat. Without doing the calculations, I'd say it depends very much on the ability of the swimmer. I'd guess the average swimmer would be able to generate an adequate force to swim vertically through a column of baby oil.

Just to see visually (googled values), a column of these substances would "float" in this order:

baby oil (least dense at 830 kg/m^3)

average human body -- 985 kg/m^3

pure water --roughly 1000 kg/m^3

seawater -- 1020 kg/m^3
posted by DoubleLune at 1:37 PM on February 7, 2015 [3 favorites]


The reason that objects float in a fluid is because gravity is pulling the liquid down, which means that the pressure of the fluid increases the deeper you go (a.k.a. a "pressure gradient"). Therefore, there is more fluid pressure pushing up on the "bottom" of you than there is pushing down on the "top" of you. The difference between those two forces is the force of buoyancy*.

Now, it turns out that the magnitude of the buoyant force works out in a very convenient way to be equal to the weight of the fluid that an object displaces. So if you jump in baby oil, the upward force on you is equal to the weight of the baby oil that would fill up a bottle the size and shape of you (there's a marketing idea for baby oil companies!). Therefore, the buoyancy force is actually less for fluids that have a lower density, since the lower the density of the fluid, the less the fluid you displace weighs.

If you weigh more than the fluid you displace (which is equivalent to saying that the your average density is greater than that of the fluid), then you sink. If you weigh less than the fluid you displace, then you float. If you weigh approximately the same, you are "neutrally buoyant".

If we're talking about baby oil made mostly of mineral oil, it would typically have a density about 80% that of water, and would therefore the buoyant force on you would only be 80% of what you'd get in water. It would indeed be more difficult to float in baby oil. Typically, I sink in water unless I take in a big lungful of air - that big lungful of air weighs very little, so it causes me to displace more liquid (increasing the buoyant force) without adding any weight to me. Equivalently, the extra air in my lungs decreases my average density. I'm not sure if I'd be able to inhale enough air to float in a fluid that has 20% less buoyant force - to be sure, I'd have to measure the minimum body density I can achieve with a full chest of air.

However, floating is one thing, swimming is another. When you swim, you use your arms and legs to push blobs of water backwards. The water (as per Newton's 3rd law, "for every action, there is an equal and opposite reaction"), therefore pushes you forwards. The ease of swimming would vary somewhat depending on things like density and viscosity of the fluid in a way that's difficult to analyze, so I'm not sure if it would be easier or harder to swim in baby oil, but it would definitely be possible.

There's no question that you'd be able to swim to the surface in a pool of baby oil, although if you're relying solely on floating to the surface to save you, you might just drown.

* for shapes with non-rectangular geometry, you can't simply take the difference between two forces, it's instead an integral of the force over the entire surface of the object, but the result is the same.
posted by Salvor Hardin at 2:10 PM on February 7, 2015 [2 favorites]


The old saying that oil and water don't mix is because oil is less dense than water.

Solubility is not related to density. Both acetone and ethanol are even less dense than baby oil and are both perfectly miscible with water. Solubility is a complicated phenomenon, but density doesn't have much to do with it.
posted by ryanrs at 2:49 PM on February 7, 2015 [11 favorites]


The old saying that oil and water don't mix is because oil is less dense than water.

I think this is incorrect. Oil and water don't mix because oil is hydrophobic, basically the oil is not good at forming bonds with the water and the water molecule prefers the company of other water molecules. Since they don't mix one has to be on top and this is oil since it is less dense. (I am dredging this up from a long time ago though.)
posted by biffa at 2:51 PM on February 7, 2015 [7 favorites]


Echoing the others, "slipperiness" is unrelated to buoyancy (floating). That said, it might be true that you would sink in baby oil, since it is less dense than water, and perhaps less dense than you. If you want real nightmare fuel though, consider drowning in foam.

on preview: hi5 biffa
posted by ryanrs at 2:52 PM on February 7, 2015


IIRC whether or not you can swim in a liquid depends on the Reynolds number, or the ratio of inertial to viscous forces, not merely the density of the liquid (though density factors into it).
posted by en forme de poire at 5:13 PM on February 7, 2015 [6 favorites]


Also note that breathing in baby oil is far more hazardous than breathing a bit of water. Even a tiny amount of baby oil in the lungs may result in lipoid pneumonia.
posted by artistic verisimilitude at 5:13 PM on February 7, 2015 [1 favorite]


Ok, I did get that it's a matter of density, but let me add to the question: If you could swim would you still drown?

Here's my thinking: People float in water, but people can swim downwards, propelling themselves against the force that would normally float you. Couldn't a person in oil swim/propel themselves up against the force pulling them down? On the other hand, I'm wondering if the reason we can swim isn't that when we press against the water to propel ourselves, the water is denser than our pressing body part and so we move and the heavier water stays still. Maybe in oil any attempt to propel yourself would create ripples/waves in the oil but not propel you?
posted by If only I had a penguin... at 11:42 AM on February 8, 2015


I'm wondering if the reason we can swim isn't that when we press against the water to propel ourselves, the water is denser than our pressing body part

No, the reason we can move through water is that water is fluid, and our bodies are (basically) solid, so the fluid moves out of the way for the solid.

The reason we can swim downward is that we can generate a force greater than the resisting force. Force = mass * acceleration -- we generate force by pushing against water, causing our bodies to accelerate.
posted by DoubleLune at 9:59 PM on February 8, 2015


So does that mean you can swim upward in oil?
posted by If only I had a penguin... at 10:06 PM on February 8, 2015


I'd guess you should be able to swim in oil pretty decently. The density is pretty similar to water (incidentally, all things being equal, increased density should actually help, not hurt, because it increases the inertial forces), and mineral oil is not that viscous in the grand scheme of things, only about an order of magnitude more than water. (See this experiment on a pool filled with syrup, which is both more viscous and denser than water. At some point the viscosity will become too much for normal swimming: compare molasses, which is ~5-10,000x more viscous; as the link notes, there was apparently a molasses spill in Boston in the early 20th century that killed 21 people, several by drowning.)
posted by en forme de poire at 12:01 AM on February 9, 2015


The old saying that oil and water don't mix is because oil is less dense than water.

biffa is absolutely correct, this statement has nothing to do with oil/water immiscibility. As a counter example, water and glycerine have a greater difference in density and viscosity, but are completely miscible. Water and oil don't mix because the oil can't participate in or break the hydrogen bond structures that liquid has. Oil is excluded from water.

You're much denser than baby oil and would sink in it.

I've actually used this phenomenon to measure the density of plant material. You weigh it in oil, sunken, then in the air. Using Archimedes' displacement, you can get the volume of the material and thus its density.
posted by bonehead at 6:51 AM on February 9, 2015


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