Diving Ketchup

Next time you go through the drive through and the person gives you way more ketchup packets than your family can use, don’t throw them away.  You can actually use them to do a fun little experiment.


  • Plastic bottle
  • Ketchup packet
  • Water
  • Cup or vase


First fill a large cup or vase with water to perform the float or sink test.  My kids had fun doing this experiment by itself.  They performed the test three times, even though we knew that only two of our packets would sink.  When ketchup packets are sealed at the factory, an air bubble get trapped inside, which makes it float.  If the ketchup packet sinks, it means that the air bubble is too small to make it float.

My son is watching the ketchup packet sink.

Next put the ketchup packet into a plastic bottle. You will need to bend the packet a bit to get it through the neck of the bottle. And please be careful not to break open the packet.

Fill the bottle completely with water, until full, and then put the lid on tightly.

I tried this experiment on four different sized bottles.  The smallest bottle (16.9 FL OZ) was too flimsy, so it didn’t work at all.  It worked great with the 1.5 L (50.7 FL OZ) & 2L bottles, however it was too difficult for my son to squeeze the bottle.  But the 24 FL OZ bottle was just right!  I’m starting to feel like Goldilocks over here. =)

To make your ketchup packet dive, just squeeze the sides of the bottle, and hold.   Then let go to make it rise again.

Why does this happen?  When you squeeze the bottle, you are increasing the pressure inside the bottle. This compresses the air bubble, which then increases the density of the ketchup packet…….making it sink. For more information visit Steve Spangler’s website.