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Diving Ketchup

Cause a packet of ketchup to rise and fall on command.

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Cause a packet of ketchup to rise and fall on command in abottle of water. People will think that you have the ability tomove objects with your mind! Telekinesis? No, just cool science!

  • Clear plastic soda bottle with cap (1-liter size works great)
  • Ketchup packets
  • Bowl
  • Water
Print Experiment


  1. First, you'll need to perform a "float or sink" test to see how the ketchup packet works. Fill a bowl with water and drop the packet into it. If it floats, great! If it sinks to the bottom, no sweat. This shows that atmospheric pressure in the packet is pressing hard enough on the air bubble inside the packet to sink it. If this happens, you get to make more trips to your favorite fast-food restaurant to find a ketchup packet that just barely floats!
  2. Scrunch the packet in half lengthwise and carefully push it into the soda bottle. Do not open the packet. Just carefully push it into the bottle without tearing the edges.
  3. Fill the bottle full to the brim with water and screw on the cap.
  4. Squeeze the sides of the bottle and hold the squeeze to make the packet sink. Let go and the packet rises. The packet of ketchup has learned to dive!

How Does It Work?

The packet floats because an air bubble gets trapped inside the packet when it's sealed at the factory. If the packet sinks when you test-float it, then the air bubble is too small to make it float.

As you squeeze the bottle and push the water against the floating packet, you compress the air bubble into a smaller space. This happens because gases are more "squishable" than liquids, so the air compresses before the water. According to the density equation (Density = Mass divided by Volume), when you decrease the volume or make the bubble of air smaller, you increase the density and the ketchup packet sinks. When you release the pressure on the bottle, the compressed air expands inside the packet (increasing the volume), the density decreases, and the diving ketchup floats to the top of the bottle.

Additional Info

Here's how to turn this demonstration into a real science experiment. Ask yourself these questions and remember the 3 C's... change, create and compare.Does the size of the bottle affect how much you have to squeeze to get the packet to sink?Do different food packs (ketchup, mustard, soy sauce) have the same density?Does the temperature of the water affect the density of the ketchup packet?

Learn how to make a classic Eye-Dropper Cartesian Diver.

Customer Reviews

daughters science fair project Review by Michelle

we tried every packet of condements we had at home (soy sauce, duck sauce, arby's sauce, tartar sauce, hot sauce)...all of these floated but would not sink when a pack of mcdonalds ketchup and viola! worked perfectly! now we're stumped as to why only ketchup...???

(Posted on March 29, 2011)

mcdonald's ketchup Review by Michele

I did this at the daycare I teach at and used the magnet trick you said to try. It was the funniest thing to watch none of the children be able to figure out how to do it. However I had 1 pack of A&W ketchup that worked and I got a bag full of Mcdonald's ketchup. None of mcdoanld's worked, they all sank.

(Posted on August 11, 2009)

Use any small package that will float Review by 2nd Grade

My son demonstrated this as his super scientist experiment. All the kids loved it. We used soy sauce package. The key is to have a package that will float.

(Posted on February 26, 2010)

IT WORKS! Review by Shan

I was a little skeptical at first.. I tried soy packets without much luck, then went to McDonalds to pick up some ketchup packets and it worked great! I had to add some salt to the water to get the packet to float.

(Posted on October 25, 2010)

I love it! Review by Samantha S.

I had to do a expirement for one of my classes. I chose this one. I didn't really think it would work. But thankfully, it did! I got an A on it. It dosn't have to be a 1 leter bottle. I used a 500ml water bottle, and it still works! Thanks!

(Posted on February 25, 2013)

Duck Sauce Packets Work! Review by Edina Renfro-Michel

We saw this on the website as we were planning my daughter's mad scientist birthday party. We decided to try it right away. We only had duck sauce packets (well, only one actually). The duck sauce barely floated on the water, but we thought we would give it a try. It worked! I had to let a tiny bit of water out of the bottle so it was easier for my daughter to squeeze, but it worked great! Great experiment and we will be using it for her party instead of the eyedroppers!

(Posted on January 29, 2012)

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