Hey Ray! Playing Around With The Density Equation

Meteorologist Ray Petelin is back with another home science lesson!

Video Transcript

- Hey, Ray. That's so cool.

RAY PETELIN: We have covered a lot of topics and done a lot of experiments.

ELIZABETH PETELIN: That's given me a lot of opportunities to make fun of my dad for you.

RAY PETELIN: And I think that's the most popular part of this. Anyhow, we are going to revisit one of those topics and that is density. And we're going to go into the equation of density to what makes it up and play around with it to make for one weird science experiment today.

We've talked about density before. Remember, if an object is more dense than what's surrounding it, it will sink. If it's less dense than what's surrounding it, it will float.

ELIZABETH PETELIN: That sounds pretty simple.

RAY PETELIN: That's why we're going to do an experiment that pushes the limits of these basic concepts. Since density is mass per unit volume, we draw the equation this way. Mass over volume equals density.

ELIZABETH PETELIN: Ew. That sounds mathy.

RAY PETELIN: It does but that math actually gives us hints as to how to control how certain things act. When you have an equation like this, it's like saying they have an inverse relationship. That means if you increase the top, the bottom is going to decrease. If you increase the bottom, the top is going to decrease. Let's show this as an experiment.


RAY PETELIN: All we need is a plastic bottle filled to the tippy top with water and something that's become a rare substance.


RAY PETELIN: Yep, a ketchup packet. And they're supposed to be very hard to come by.

ELIZABETH PETELIN: But we have a whole drawer though.

RAY PETELIN: Sshh. Let's continue with the science. You put the ketchup packet in the bottle and put the lid on. What's happening here?


RAY PETELIN: It is. There's a little air in that ketchup packet so it makes it less dense than the water around it so it floats. Now give the bottle a squeeze.


RAY PETELIN: It sinks when you squeeze the bottle so you must be doing something to increase the density of the ketchup packet. Now let go. And you see the ketchup packet floats again.

ELIZABETH PETELIN: All I did was squeeze the bottle.

RAY PETELIN: And when you squeeze the bottle, you decrease the volume so that means?

ELIZABETH PETELIN: You increase the mass?

- You increase the mass of the ketchup packet. When the volume is decreased, the mass is increased just like our equation. Remember, we filled the bottle to the tippy top and that means there's no air in the bottle except for the little bit of air that's in the ketchup packet. That's what causes it to initially float.

Once you squeeze the bottle though, the water squeezes the ketchup packet. This compresses the air in the packet so it can't take up as much space and that makes the packet more dense than the water. When you stop squeezing the bottle, the opposite becomes true and the ketchup packet floats again.

ELIZABETH PETELIN: It's just like magic.

RAY PETELIN: It is. And it's one of those experiments that you could treat like a magic trick especially if pretend to move the packet with your mind.

ELIZABETH PETELIN: Quit being weird.

RAY PETELIN: All right, I'll stop being weird. We're going to put some tips on how to make this experiment work best on www.kdka.com. Reporting from home.

ELIZABETH PETELIN: I'm Elizabeth Petelin.

RAY PETELIN: I'm meteorologist Ray Petelin. Floats, floats.