You can make a pack of ketchup float and sink
at your command while it's sealed inside a bottle!
* A 1 liter plastic bottle
* Ketchup pack from a fast food restaurant
* Salt (using Kosher salt helps keep the water from becoming foggy)
This experiment is all about buoyancy and density. Buoyancy describes whether objects float or sink. This usually describes how things float in liquids, but it can also describe how things float or sink in and various gasses.
Density deals with the amount of mass an object has. Adding salt to the water adjusted the water's density to get the ketchup to float. Sound complicated? It is, but here's the basics on the ketchup demo...there is a little bubble inside of the ketchup packet. As we know bubbles float, and the bubble in the ketchup sometimes keeps the heavy packet from sinking. When you squeeze the bottle hard enough, you put pressure on the packet. That causes the bubble to get smaller and the entire packet to become MORE DENSE than the water around it and the packet sinks. When you release the pressure, the bubble expands, making the packet less dense (and more buoyant) and, alas, it floats back up. This demonstration is sometimes known as a CARTESIAN DIVER.
The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:
1. Do different food packs (ketchup, mustard, soy sauce) 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?