Kitchen Experiment: Magic Ketchup

What would your little minds think if you told them that they could make a pack of ketchup float and sink at their command while it was sealed inside a one liter bottle? I know, they'd tell you that that was impossible! Lucky for you, you can work with them to prove them wrong and teach them a little about buoyancy and density in the process. Sounds like a win-win to me.

So let's get started! Here's what you'll need:

• 1 liter plastic bottle
• Ketchup packet from a fast food restaurant
• Salt (using Kosher salt will keep your water from become foggy)

Here's what you'll do:

1. Remove all labels from the plastic bottle and fill it to the top with water.
2. Add the ketchup pack to the bottle.
3. If the ketchup packet floats, you're ready to move on to step four. If the ketchup packet doesn't float and starts to sink, skip to step five.
4. For the floating ketchup packet, simply screw the cap on the bottle and squeeze the sides of the bottle hard. If the ketchup sinks when you squeeze it and floats when you release it, you're in business and ready to show off your magical powers! If it doesn't sink when  you squeeze the bottle, try a different ketchup packet or a mustard or soy sauce packet.
5. If the ketchup packet sunk when you put it in the bottle, add around 3 tbsp. of salt to the bottle and shake it until the salt dissolves.
6. Continuing adding sale a few tablespoons at a time until the ketchup packet is just barely floating at the top.
7. Once it's consistently floating, make sure the bottle is filled to the top with water and then cap it tightly.
8. Now squeeze the bottle. The magic ketchup should sink when you squeeze the bottle and float up when you release it. If you get really good, you can get it to stop in the middle of the bottle!

So how does it work? What' behind the magic? This entire experiment revolves around two things: buoyancy and density. Buoyancy describes whether objects float or sink and density deals with the amount of mass in an object. Adding salt to the water adjusted its density and got the ketchup packet to float. There is a little bubble inside of the ketchup packet and, since we know bubbles float, this bubble is what keeps the packet from sinking. But when you squeeze the bottle, you put pressure on the packet that results in  the bubble getting smaller and the packet becoming more dense. Thus, it sinks. When you release the pressure the bubble expands, the packet becomes less dense and more buoyant and floats back to the top.

To take this experiment to the next level, try answering these questions:

1. Do different food packets (ketchup, mustard, soy sauce, relish, mayo, etc.) have the same density?
2. Does the temperature of the water affect the density of the ketchup packet?
3. Does the size of the bottle affect how much you have to squeeze to get the packet to sink?