Density (3)

Floating and Sinking WALT: Investigate why some things float I must be able to carry out a practical to test how density relates to whether things float I should be able to design an experiment to test how the density of salt water compares to fresh water

Can you think of how you would work out the difference in the density of saltwater and freshwater? You could measure the mass and volume of each You could use a hydrometer – watch the demo

In pairs, discuss and write down: How do massive cruise liners stay afloat? Why do some liquids separate? How could you make a lava lamp using oil, coloured water and salt?

If an object’s density is less than the density of the liquid it is in, it will float. If the density is more than the density of the liquid, it will sink

Now we are going to make a lava lamp………

Clear jar with lid Water Food colouring Vegetable oil Salt Torch YOU WILL NEED Clear jar with lid Water Food colouring Vegetable oil Salt Torch Fill the jar three-quarters full of water. Add drops of food colouring until you like the colour you see. A few drops go a long way! Fill the jar almost to the top with vegetable oil and let the mixture separate. Pour salt into the jar until you see the cool lava lamp effect. When the bubbles stop, add more salt to see it again. Shine a flashlight behind the jar to watch your lava lamp really glow!

HOW DOES IT WORK? The secret behind the lamp’s “lava” is science. Oil is lighter, or less dense, than water, so it rises to the surface. Salt is heavier, or more dense, than water, and sinks to the bottom. When you add the salt, blobs of oil attach to the grains and sink. Then the salt dissolves, and the oil returns to the top. The result? A liquid show for the eyes.

When finished Write a method and explanation of how a lava lamp works Invent 5 density equation calculations and then answer them neatly.