18, Buoyancy and density

Telekinesis Bottle

This is the last experiment in the book. After this, you can just read till the end!

Ingredients

  • 1 small Ketchup packet like you find at burger restaurants (mustard or soy sauce packet will also do)
  • 1 litre empty plastic bottle with cap.
  • water

What to do:

Pour tap water into the plastic bottle almost until the brim.

telekinesis Place the ketchup packet inside. Make sure that the packet floats. If the packet does not float, add 3 teaspoons of salt into the water and try again.

Put the cap back on the bottle.

Squeeze the bottle gently and watch the packet sink. Experiment with the pressure to get the packet to rise and sink according to your whim. You can even pretend to use your other hand to command the packet to rise and fall or stay steady.

What is happening?

This is about “buoyancy”, which describes whether or not objects float in a substance, and how it is affected by changes in density. The more dense an object is, the more likely it will sink, and the lighter it is the more likely it will float.

Inside the packet is a little bit of air, which is lighter than water and thus will cause the packet to flat. In case it doesn't, we simply add some salt to the mix in order to make the water denser.

By squeezing the bottle, you also add a little pressure into the mix. This causes the bubble in the packet to shrink, which makes the sauce packet more dense, and thus will sink down in the water. Of course, releasing the pressure makes it rise up.