Magic Ketchup Experiment

With my 5 year old in kindergarten each day, along with Girl Scouts, soccer, and swimming lessons, there isn't as much time for science experiments as there was this summer.  We did, however, find some time on an afternoon last weekend to complete the Magic Ketchup Experiment.  In this experiment, one is testing the density of single serving ketchup packets.  First fill a two liter bottle full of water and drop in a small, sealed, packet of ketchup.  Depending on the packet, it may sink, or it may float.  It all depends on the initial density of the packet.  If it's more dense that water, it sinks.  If it's less dense, it rises.  Ours initially sank.  If the packet sinks, add salt to the water until the packet rises.  Adding salt to the water increases the water density.  Once the water density exceeds that of the ketchup packet, the packet begins to rise.  Now you're ready.

Have your child, or do it together, squeeze the two liter bottle.  By squeezing the bottle, you increase the water pressure which applies pressure to the ketchup packet and contracts it.  You probably won't see the packet contract, but the extra pressure contracts it ever so slightly.  Assuming you didn't add too much salt in the earlier steps, the ketchup will contract such that its density is now greater than that of the salt water.  It will begin to sink.  Release your hands, decreasing the pressure on the packet and it rises again.  Keep repeating this process to watch the packet rise, fall, rise, fall, etc.  See below for our video.

This is a fun little experiment that lets you talk to your child about density and pressure.  My daughter thought this was cool.  We also tried Taco Bell hot sauce, soy sauce, and mustard packets, but they wouldn't sink when we squeezed the bottle.  The water density was already much greater than that of the packet.  We needed to start over with fresh water in the two liter bottle.  We didn't have any time left in the afternoon, so we'll try these on a later date.