What is Needed
- Condiment Packet (Ketchup from Wendy’s or Soy Sauce is what I use)
- Two-liter bottle
What to Do
- Place the condiment packet in the two-liter bottle, and fill it up, all the way to the top.
- Screw the top of the bottle on, hard. If the packet floats, you are probably OK.
- If it sinks, you are going to need to try a different packet.
- Ketchup packets seem to work well for me, so you may need to try something else depending on what part of the country you live in.
- Your local air pressure makes a difference!
- Next, squeeze the bottle.
- If you squeeze it hard enough, the packet should sink.
- If you can’t make it sink (mayonnaise packets seem to float no matter how hard you squeeze), you will need to try another packet.
Once you get just the right packet, it will float when you aren’t squeezing the bottle, and sink when you do. You can make it go up and down with very little effort.
What is Happening?
There is a small air bubble inside the packet. When the packet is inside the bottle and you are not squeezing, the bubble is large enough that it will make the packet float very nicely.
However, when you squeeze the bottle, you increase the pressure inside the bottle. This will compress the air bubble, which will increase the density of the packet. The packet will now sink.
This is a classic experiment called the Cartesian diver.
Submarines use a similar principle to control their buoyancy, as do some fish.