MAYBE YOU HAVE watched Stranger Things but maybe you haven't. I've seen it, and I thought it was great—and not just because there's lots of science in it. Don't worry, I'm not going to talk about multiple universes or quantum tunneling. Instead I am going to talk about salt.
Small spoiler alert (but not really a spoiler): In season 1, the Stranger Things kids need to build a makeshift sensory deprivation tank. The essential component of this "tank" is a kiddie pool filled with water such that a person can easily float. Of course, normal water will make a human just barely float. To fix this problem, they add a bunch of salt to increase the liquid density to accommodate a floating human. According to Mr. Clark (their science teacher), they need 1,500 pounds of salt.
But was he right? Let's take a look at the science.
Floating and Density
Why do things float? If an object is stationary at the surface of water (or any liquid), then the net force on that object is zero. Of course there is a gravitational force pulling down, so that must mean there is some other force (with an equal magnitude) pushing up. That force is the buoyancy force. But how does it work? Let's start with an example.
Here is a block of water floating in water. Yes, water floats.