This is a super simple, fun Halloween density investigation, perfect for introducing the concept of liquids having different densities and for practising making and testing predictions. All you need to do is set up an easy density jar and try to find a spooky object for each layer.
How to make a density jar
What you need
Empty bottle or jar
Oil – we used very cheap vegetable oil.
Halloween objects to test – we used plastic spiders, eyeball bouncy balls and decorative foil ghosts
Half fill your container with water, then add some oil. What do you notice?
Carefully drop your objects into the jar, what happens? Can you find something to float on each layer?
Were your predictions correct?
See this post for a full explanation about density.
Why do oil and water not mix?
This is because water is a polar molecule – it’s structure means that is has a positive charge one end and a negative charge the other. Water molecules stick together because the positive end of one water molecule is attracted to the negative end of another. An oil molecule has a different structure, it is non polar meaning that its charge is more evenly spread out, so the oil is not attracted to water. We call it hydrophobic (water fearing) so it tries to get as far away from water as possible.