Add one drop of food colouring to the jar, what happens now? Is the drop in the oil or in the water? Does the colour spread and how?
Shake the salt or sugar on top of the oil in generous streams and sit back to watch your lava lamp in action.
Oil is lighter and less dense than water so it floats. Something that has a higher density than water will sink.
Density is a measurement of the mass of a given volume. Think about a sponge. Most artificial sponges today are made of a foamed plastic. If you have a giant one kilo sponge, and if you melted it down to a plastic soup with all the bubbles gone, it will be much smaller, but it will still weigh one kilo. It is now denser. Water is denser than oil as there is more of it in a given volume.
Water and oil are immiscible liquids. This means they don't mix. Oil and water are very different liquids that prefer to stick to themselves.
Salt and sugar are heavier than water so when you pour them into the liquid, they sink to the bottom. As they sink, they carry a blob of oil with them.
The sugar and salt than release the oil, and it floats back up to the top.
As the oil blobs float back up to the top, this experiment looks very much like a lava lamp. A lava lamp however, contains hot wax which rises to the top of the lamp, cools and then falls.
You can do this experiment when waiting for your meal in a restaurant. Or, outside the kitchen, this piece of science is important when cleaning up damaging oil spills.
An oil spill is where oil (such as you might use in your car) is accidentally spilled into an ecosystem. Oil spills can be extremely harmful to animals and plants. They can happen in rivers, bays and oceans when vessels such as tankers, barges and pipelines have accidents.
When oil is spilt, it spreads out across the water surface to form a thin layer called an oil slick. As it spreads, the oil layer becomes thinner and thinner, finally becoming a very thin rainbow sheen on the surface of the water.
To help clean the oil up, rescuers use the fact that it is less dense than water. The oil will sit on the surface of the water and floating barriers or booms can collect the oil and stop it from spreading. The oil can also be sucked up with a special vacuum. Boats called skimmers can skim the spilled oil from the water surface. Big sponges can soak up oil from the water surface, and sometimes they even burn the oil while it sits on the surface of the water.