Imagine a tiny, mysterious object that can sink or float at your command. It might sound like magic, but it's actually science! Turn an ordinary soy sauce packet into an extraordinary science experiment! Learn how to create a Cartesian diver and explore the fascinating world of density and pressure.
What You'll Need:
A clear plastic bottle with cap (like a water bottle)
A soy sauce packet with clear side and air bubble inside packet
can use other packets, but won’t be able to see what is going on inside the packet!
Water
Let's Dive In!
Prepare your bottle: First, add the unopened soy sauce packet to the bottle, you may need to squish the sides if the opening is narrow. Now fill the bottle to the brim with water. The water should be overflowing, we don’t want any air bubbles inside the bottle! See images below for what we want (and don’t want).
Seal the deal: Screw the cap on tightly, some water may spill and this is okay. We want the bottle completely full of water, sealed and closed; this is important!!
The Magic Begins
Now, here's where the fun starts:
Squeeze it! Gently squeeze the bottle. Watch as your soy sauce diver magically sinks!
If the packet is not sinking, first check for any air bubbles inside the bottle - if there is, then add more water and try again. If it is still not sinking, then the air pocket inside of the packet may be too large, so try another packet.
If the packet sinks right away, the air pocket inside is too small so try another packet.
Release it! Let go of the bottle. Your diver should rise back to the surface.
Why Does It Work? It’s all about density and pressure!!
Applying pressure to the bottle raises the water pressure surrounding the soy sauce packet. This increased pressure forces the air within the packet to compress, reducing its volume without changing the amount of air. As a result, the packet becomes denser, changing its buoyancy so that it sinks through the water. Density is the ratio of mass and volume for any given object, even air! When you release the bottle, the water pressure returns to normal, the air in the packet expands, and the packet becomes less dense, causing it to rise.
Density is a physical parameter for any object. It is so unique that scientists can use it to identify unknown materials such as precious metals! The mass of gold (0.69 lb per square inch) is very different from copper (0.32 lb/sq.inch), so it will sink at a different rate. But remember, density is the ratio of mass (how much there is) vs. the volume (how much space it takes up). Another way to think about this is by the surface an object has. When you are swimming, do you float better by laying flat or by curling up into a ball? Laying flat of course! When you spread out your body by laying flat, the amount of weight per square inch of your body is less, allowing you to float (for most of us). But when you curl up into a ball, this amount is much higher, so you sink! Even though summer is almost over, you should try this out next time you’re out swimming with (or without) your kids!
Essentially, the air pocket acts as a sensitive barometer, responding to changes in pressure and affecting the buoyancy of the soy sauce packet.
SAFETY- very minimal, excellent activity to do with small children - just make sure you have enough bottles prepped, because once they start they won’t want to give it up!
Disposal: none, just water and sauce packets - which are still good to use after the experiment is over!
For more fun:
How many divers can you put inside one bottle? If one packet sinks faster than the others, take a closer look at the air bubble inside the packet - what is different?
Now experiment with different types of sauce packets (ketchup, honey, mustard, etc.) to see if they behave differently. Packet does not need to have a visible air pocket, it just needs to float inside the bottle before you squeeze it. If it sinks before you squeeze, what does this tell you?
Need one more idea? You can also experiment with different temperatures for the water inside the bottle, what happens if it is ice cold? Almost boiling? Does the packet still sink/float the same as room temperature water?
For older kids - Continue (or start) using your science journal and take notes to record your observations from each experiment you do. “Remember kids, the only difference between science and screwing around….is writing it down!” Adam Savage, MythBusters.
Keywords: Cartesian diver, buoyancy, density, mass, volume, pressure
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